Preface

Working with both Object-Oriented software and Relational Databases can be cumbersome and time-consuming. Development costs are significantly higher due to a paradigm mismatch between how data is represented in objects versus relational databases. Hibernate is an Object/Relational Mapping solution for Java environments. The term Object/Relational Mapping refers to the technique of mapping data from an object model representation to a relational data model representation (and vice versa).

Hibernate not only takes care of the mapping from Java classes to database tables (and from Java data types to SQL data types), but also provides data query and retrieval facilities. It can significantly reduce development time otherwise spent with manual data handling in SQL and JDBC. Hibernate’s design goal is to relieve the developer from 95% of common data persistence-related programming tasks by eliminating the need for manual, hand-crafted data processing using SQL and JDBC. However, unlike many other persistence solutions, Hibernate does not hide the power of SQL from you and guarantees that your investment in relational technology and knowledge is as valid as always.

Hibernate may not be the best solution for data-centric applications that only use stored-procedures to implement the business logic in the database, it is most useful with object-oriented domain models and business logic in the Java-based middle-tier. However, Hibernate can certainly help you to remove or encapsulate vendor-specific SQL code and will help with the common task of result set translation from a tabular representation to a graph of objects.

System Requirements

Hibernate 6.4 requires at least Java 11 and JDBC 4.2.

Getting Started

While a strong background in SQL is not required to use Hibernate, a basic understanding of its concepts is useful - especially the principles of data modeling. Understanding the basics of transactions and design patterns such as Unit of Work are important as well.

New users may want to first look at the tutorial-style Quick Start guide.

This User Guide is really more of a reference guide. For a more high-level discussion of the most used features of Hibernate, see the Introduction to Hibernate guide.

There is also a series of topical guides providing deep dives into various topics such as logging, compatibility and support, etc.

Get Involved

  • Use Hibernate and report any bugs or issues you find. See Issue Tracker for details.

  • Try your hand at fixing some bugs or implementing enhancements. Again, see Issue Tracker.

  • Engage with the community using the methods listed in the Community section.

  • Help improve this documentation. Contact us on the developer mailing list or Zulip if you have interest.

  • Spread the word. Let the rest of your organization know about the benefits of Hibernate.

1. Compatibility

1.1. Dependencies

Hibernate 6.4.4.Final requires the following dependencies (among others):

Table 1. Compatible versions of dependencies

Version

Java Runtime

11, 17 or 21

Jakarta Persistence

3.1.0

JDBC (bundled with the Java Runtime)

4.2

Find more information for all versions of Hibernate on our compatibility matrix.

The compatibility policy may also be of interest.

If you get Hibernate from Maven Central, it is recommended to import Hibernate Platform as part of your dependency management to keep all its artifact versions aligned.

Gradle
dependencies {
  implementation platform "org.hibernate.orm:hibernate-platform:6.4.4.Final"

  // use the versions from the platform
  implementation "org.hibernate.orm:hibernate-core"
  implementation "jakarta.transaction:jakarta.transaction-api"
}
Maven
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.hibernate.orm</groupId>
            <artifactId>hibernate-platform</artifactId>
            <version>6.4.4.Final</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
<!-- use the versions from the platform -->
<dependencies>
    <dependency>
        <groupId>org.hibernate.orm</groupId>
        <artifactId>hibernate-core</artifactId>
    </dependency>
    <dependency>
        <groupId>jakarta.transaction</groupId>
        <artifactId>jakarta.transaction-api</artifactId>
    </dependency>
</dependencies>

1.2. Database

Hibernate 6.4.4.Final is compatible with the following database versions, provided you use the corresponding dialects:

Dialect Minimum Database Version

CockroachDialect

22.2

DB2Dialect

10.5

DB2iDialect

7.1

DB2zDialect

12.1

DerbyDialect

10.15.2

GenericDialect

0.0

H2Dialect

2.1.214

HANAColumnStoreDialect

0.0

HANARowStoreDialect

0.0

HSQLDialect

2.6.1

MariaDBDialect

10.4

MySQLDialect

8.0

OracleDialect

19.0

PostgreSQLDialect

12.0

PostgresPlusDialect

12.0

SQLServerDialect

11.0

SpannerDialect

0.0

SybaseASEDialect

16.0

SybaseDialect

16.0

TiDBDialect

5.4

2. Architecture

2.1. Overview

Data Access Layers

Hibernate, as an ORM solution, effectively "sits between" the Java application data access layer and the Relational Database, as can be seen in the diagram above. The Java application makes use of the Hibernate APIs to load, store, query, etc. its domain data. Here we will introduce the essential Hibernate APIs. This will be a brief introduction; we will discuss these contracts in detail later.

As a Jakarta Persistence provider, Hibernate implements the Java Persistence API specifications and the association between Jakarta Persistence interfaces and Hibernate specific implementations can be visualized in the following diagram:

image

SessionFactory (org.hibernate.SessionFactory)

A thread-safe (and immutable) representation of the mapping of the application domain model to a database. Acts as a factory for org.hibernate.Session instances. The EntityManagerFactory is the Jakarta Persistence equivalent of a SessionFactory and basically, those two converge into the same SessionFactory implementation.

A SessionFactory is very expensive to create, so, for any given database, the application should have only one associated SessionFactory. The SessionFactory maintains services that Hibernate uses across all Session(s) such as second level caches, connection pools, transaction system integrations, etc.

Session (org.hibernate.Session)

A single-threaded, short-lived object conceptually modeling a "Unit of Work" (PoEAA). In Jakarta Persistence nomenclature, the Session is represented by an EntityManager.

Behind the scenes, the Hibernate Session wraps a JDBC java.sql.Connection and acts as a factory for org.hibernate.Transaction instances. It maintains a generally "repeatable read" persistence context (first level cache) of the application domain model.

Transaction (org.hibernate.Transaction)

A single-threaded, short-lived object used by the application to demarcate individual physical transaction boundaries. EntityTransaction is the Jakarta Persistence equivalent and both act as an abstraction API to isolate the application from the underlying transaction system in use (JDBC or JTA).

3. Domain Model

The term domain model comes from the realm of data modeling. It is the model that ultimately describes the problem domain you are working in. Sometimes you will also hear the term persistent classes.

Ultimately the application domain model is the central character in an ORM. They make up the classes you wish to map. Hibernate works best if these classes follow the Plain Old Java Object (POJO) / JavaBean programming model. However, none of these rules are hard requirements. Indeed, Hibernate assumes very little about the nature of your persistent objects. You can express a domain model in other ways (using trees of java.util.Map instances, for example).

Historically applications using Hibernate would have used its proprietary XML mapping file format for this purpose. With the coming of Jakarta Persistence, most of this information is now defined in a way that is portable across ORM/Jakarta Persistence providers using annotations (and/or standardized XML format). This chapter will focus on Jakarta Persistence mapping where possible. For Hibernate mapping features not supported by Jakarta Persistence we will prefer Hibernate extension annotations.

This chapter mostly uses "implicit naming" for table names, column names, etc. For details on adjusting these names see Naming strategies.

3.1. Mapping types

Hibernate understands both the Java and JDBC representations of application data. The ability to read/write this data from/to the database is the function of a Hibernate type. A type, in this usage, is an implementation of the org.hibernate.type.Type interface. This Hibernate type also describes various behavioral aspects of the Java type such as how to check for equality, how to clone values, etc.

Usage of the word type

The Hibernate type is neither a Java type nor a SQL data type. It provides information about mapping a Java type to an SQL type as well as how to persist and fetch a given Java type to and from a relational database.

When you encounter the term type in discussions of Hibernate, it may refer to the Java type, the JDBC type, or the Hibernate type, depending on the context.

To help understand the type categorizations, let’s look at a simple table and domain model that we wish to map.

Example 1. A simple table and domain model
create table Contact (
    id integer not null,
    first varchar(255),
    last varchar(255),
    middle varchar(255),
    notes varchar(255),
    starred boolean not null,
    website varchar(255),
    primary key (id)
)
@Entity(name = "Contact")
public static class Contact {

	@Id
	private Integer id;

	private Name name;

	private String notes;

	private URL website;

	private boolean starred;

	//Getters and setters are omitted for brevity
}

@Embeddable
public class Name {

	private String firstName;

	private String middleName;

	private String lastName;

	// getters and setters omitted
}

In the broadest sense, Hibernate categorizes types into two groups:

3.1.1. Value types

A value type is a piece of data that does not define its own lifecycle. It is, in effect, owned by an entity, which defines its lifecycle.

Looked at another way, all the state of an entity is made up entirely of value types. These state fields or JavaBean properties are termed persistent attributes. The persistent attributes of the Contact class are value types.

Value types are further classified into three sub-categories:

Basic types

in mapping the Contact table, all attributes except for name would be basic types. Basic types are discussed in detail in Basic types

Embeddable types

the name attribute is an example of an embeddable type, which is discussed in details in Embeddable types

Collection types

although not featured in the aforementioned example, collection types are also a distinct category among value types. Collection types are further discussed in Collections

3.1.2. Entity types

Entities, by nature of their unique identifier, exist independently of other objects whereas values do not. Entities are domain model classes which correlate to rows in a database table, using a unique identifier. Because of the requirement for a unique identifier, entities exist independently and define their own lifecycle. The Contact class itself would be an example of an entity.

Mapping entities is discussed in detail in Entity types.

3.2. Basic values

A basic type is a mapping between a Java type and a single database column.

Hibernate can map many standard Java types (Integer, String, etc.) as basic types. The mapping for many come from tables B-3 and B-4 in the JDBC specification[jdbc]. Others (URL as VARCHAR, e.g.) simply make sense.

Additionally, Hibernate provides multiple, flexible ways to indicate how the Java type should be mapped to the database.

The Jakarta Persistence specification strictly limits the Java types that can be marked as basic to the following:

Category Package Types

Java primitive types

boolean, int, double, etc.

Primitive wrappers

java.lang

Boolean, Integer, Double, etc.

Strings

java.lang

String

Arbitrary-precision numeric types

java.math

BigInteger and BigDecimal

Date/time types

java.time

LocalDate, LocalTime, LocalDateTime, OffsetTime, OffsetDateTime, Instant

Deprecated date/time types

java.util

Date and Calendar

Deprecated date/time types from

java.sql

Date, Time, Timestamp

Byte and character arrays

byte[] or Byte[], char[] or Character[]

Java enumerated types

Any enum

Serializable types

Any type that implements java.io.Serializable[1]

If provider portability is a concern, you should stick to just these basic types.

Java Persistence 2.1 introduced the jakarta.persistence.AttributeConverter providing support for handling types beyond those defined in the specification. See AttributeConverters for more on this topic.

3.2.1. @Basic

Strictly speaking, a basic type is denoted by the jakarta.persistence.Basic annotation.

Generally, the @Basic annotation can be ignored as it is assumed by default. Both of the following examples are ultimately the same.

Example 2. @Basic explicit
@Entity(name = "Product")
public class Product {

	@Id
	@Basic
	private Integer id;

	@Basic
	private String sku;

	@Basic
	private String name;

	@Basic
	private String description;
}
Example 3. @Basic implied
@Entity(name = "Product")
public class Product {

	@Id
	private Integer id;

	private String sku;

	private String name;

	private String description;
}

The @Basic annotation defines 2 attributes.

optional - boolean (defaults to true)

Defines whether this attribute allows nulls. Jakarta Persistence defines this as "a hint", which means the provider is free to ignore it. Jakarta Persistence also says that it will be ignored if the type is primitive. As long as the type is not primitive, Hibernate will honor this value. Works in conjunction with @Column#nullable - see @Column.

fetch - FetchType (defaults to EAGER)

Defines whether this attribute should be fetched eagerly or lazily. EAGER indicates that the value will be fetched as part of loading the owner. LAZY values are fetched only when the value is accessed. Jakarta Persistence requires providers to support EAGER, while support for LAZY is optional meaning that a provider is free to not support it. Hibernate supports lazy loading of basic values as long as you are using its bytecode enhancement support.

3.2.2. @Column

Jakarta Persistence defines rules for implicitly determining the name of tables and columns. For a detailed discussion of implicit naming see Naming strategies.

For basic type attributes, the implicit naming rule is that the column name is the same as the attribute name. If that implicit naming rule does not meet your requirements, you can explicitly tell Hibernate (and other providers) the column name to use.

Example 4. Explicit column naming
@Entity(name = "Product")
public class Product {

	@Id
	private Integer id;

	private String sku;

	private String name;

	@Column(name = "NOTES")
	private String description;
}

Here we use @Column to explicitly map the description attribute to the NOTES column, as opposed to the implicit column name description. See Naming strategies for additional details.

The @Column annotation defines other mapping information as well. See its Javadocs for details.

3.2.3. @Formula

@Formula allows mapping any database computed value as a virtual read-only column.

  • The @Formula annotation takes a native SQL clause which may affect database portability.

  • @Formula is a Hibernate-specific mapping construct and not covered by Jakarta Persistence. Applications interested in portability should avoid its use.

Example 5. @Formula mapping usage
@Entity(name = "Account")
public static class Account {

	@Id
	private Long id;

	private Double credit;

	private Double rate;

	@Formula(value = "credit * rate")
	private Double interest;

	//Getters and setters omitted for brevity

}

When loading the Account entity, Hibernate is going to calculate the interest property using the configured @Formula:

Example 6. Persisting an entity with a @Formula mapping
doInJPA(this::entityManagerFactory, entityManager -> {
	Account account = new Account();
	account.setId(1L);
	account.setCredit(5000d);
	account.setRate(1.25 / 100);
	entityManager.persist(account);
});

doInJPA(this::entityManagerFactory, entityManager -> {
	Account account = entityManager.find(Account.class, 1L);
	assertEquals(Double.valueOf(62.5d), account.getInterest());
});
INSERT INTO Account (credit, rate, id)
VALUES (5000.0, 0.0125, 1)

SELECT
    a.id as id1_0_0_,
    a.credit as credit2_0_0_,
    a.rate as rate3_0_0_,
    a.credit * a.rate as formula0_0_
FROM
    Account a
WHERE
    a.id = 1

The SQL fragment defined by the @Formula annotation can be as complex as you want, and it can even include sub-selects.

3.2.4. Mapping basic values

To deal with values of basic type, Hibernate needs to understand a few things about the mapping:

  • The capabilities of the Java type. For example:

    • How to compare values

    • How to calculate a hash-code

    • How to coerce values of this type to another type

  • The JDBC type it should use

    • How to bind values to JDBC statements

    • How to extract from JDBC results

  • Any conversion it should perform on the value to/from the database

  • The mutability of the value - whether the internal state can change like java.util.Date or is immutable like java.lang.String

This section covers how Hibernate determines these pieces and how to influence that determination process.

The following sections focus on approaches introduced in version 6 to influence how Hibernate will map basic value to the database.

This includes removal of the following deprecated legacy annotations:

  • @TypeDef

  • @TypeDefs

  • @CollectionId#type

  • @AnyMetaDef#metaType

  • @AnyMetaDef#idType

See the 6.0 migration guide for discussions about migrating uses of these annotations

The new annotations added as part of 6.0 support composing mappings in annotations through "meta-annotations".

Looking at this example, how does Hibernate know what mapping to use for these attributes? The annotations do not really provide much information.

This is an illustration of Hibernate’s implicit basic-type resolution, which is a series of checks to determine the appropriate mapping to use. Describing the complete process for implicit resolution is beyond the scope of this documentation[2].

This is primarily driven by the Java type defined for the basic type, which can generally be determined through reflection. Is the Java type an enum? Is it temporal? These answers can indicate certain mappings be used.

The fallback is to map the value to the "recommended" JDBC type.

Worst case, if the Java type is Serializable Hibernate will try to handle it via binary serialization.

For cases where the Java type is not a standard type or if some specialized handling is desired, Hibernate provides 2 main approaches to influence this mapping resolution:

  • A compositional approach using a combination of one-or-more annotations to describe specific aspects of the mapping. This approach is covered in Compositional basic mapping.

  • The UserType contract, which is covered in Custom type mapping

These 2 approaches should be considered mutually exclusive. A custom UserType will always take precedence over compositional annotations.

The next few sections look at common, standard Java types and discusses various ways to map them. See Case Study : BitSet for examples of mapping BitSet as a basic type using all of these approaches.

3.2.5. Enums

Hibernate supports the mapping of Java enums as basic value types in a number of different ways.

@Enumerated

The original Jakarta Persistence-compliant way to map enums was via the @Enumerated or @MapKeyEnumerated annotations, working on the principle that the enum values are stored according to one of 2 strategies indicated by jakarta.persistence.EnumType:

ORDINAL

stored according to the enum value’s ordinal position within the enum class, as indicated by java.lang.Enum#ordinal

STRING

stored according to the enum value’s name, as indicated by java.lang.Enum#name

Assuming the following enumeration:

Example 7. PhoneType enumeration
public enum PhoneType {
	LAND_LINE,
	MOBILE;
}

In the ORDINAL example, the phone_type column is defined as a (nullable) INTEGER type and would hold:

NULL

For null values

0

For the LAND_LINE enum

1

For the MOBILE enum

Example 8. @Enumerated(ORDINAL) example
@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	@Column(name = "phone_number")
	private String number;

	@Enumerated(EnumType.ORDINAL)
	@Column(name = "phone_type")
	private PhoneType type;

	//Getters and setters are omitted for brevity

}

When persisting this entity, Hibernate generates the following SQL statement:

Example 9. Persisting an entity with an @Enumerated(ORDINAL) mapping
Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("123-456-78990");
phone.setType(PhoneType.MOBILE);
entityManager.persist(phone);
INSERT INTO Phone (phone_number, phone_type, id)
VALUES ('123-456-78990', 1, 1)

In the STRING example, the phone_type column is defined as a (nullable) VARCHAR type and would hold:

NULL

For null values

LAND_LINE

For the LAND_LINE enum

MOBILE

For the MOBILE enum

Example 10. @Enumerated(STRING) example
@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	@Column(name = "phone_number")
	private String number;

	@Enumerated(EnumType.STRING)
	@Column(name = "phone_type")
	private PhoneType type;

	//Getters and setters are omitted for brevity

}

Persisting the same entity as in the @Enumerated(ORDINAL) example, Hibernate generates the following SQL statement:

Example 11. Persisting an entity with an @Enumerated(STRING) mapping
INSERT INTO Phone (phone_number, phone_type, id)
VALUES ('123-456-78990', 'MOBILE', 1)
Using AttributeConverter

Let’s consider the following Gender enum which stores its values using the 'M' and 'F' codes.

Example 12. Enum with a custom constructor
public enum Gender {

    MALE('M'),
    FEMALE('F');

    private final char code;

    Gender(char code) {
        this.code = code;
    }

    public static Gender fromCode(char code) {
        if (code == 'M' || code == 'm') {
            return MALE;
        }
        if (code == 'F' || code == 'f') {
            return FEMALE;
        }
        throw new UnsupportedOperationException(
            "The code " + code + " is not supported!"
       );
    }

    public char getCode() {
        return code;
    }
}

You can map enums in a Jakarta Persistence compliant way using a Jakarta Persistence AttributeConverter.

Example 13. Enum mapping with AttributeConverter example
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@Convert(converter = GenderConverter.class)
	public Gender gender;

	//Getters and setters are omitted for brevity

}

@Converter
public static class GenderConverter
		implements AttributeConverter<Gender, Character> {

	public Character convertToDatabaseColumn(Gender value) {
		if (value == null) {
			return null;
		}

		return value.getCode();
	}

	public Gender convertToEntityAttribute(Character value) {
		if (value == null) {
			return null;
		}

		return Gender.fromCode(value);
	}
}

Here, the gender column is defined as a CHAR type and would hold:

NULL

For null values

'M'

For the MALE enum

'F'

For the FEMALE enum

For additional details on using AttributeConverters, see AttributeConverters section.

Jakarta Persistence explicitly disallows the use of an AttributeConverter with an attribute marked as @Enumerated.

So, when using the AttributeConverter approach, be sure not to mark the attribute as @Enumerated.

Custom type

You can also map enums using a Hibernate custom type mapping. Let’s again revisit the Gender enum example, this time using a custom Type to store the more standardized 'M' and 'F' codes.

Example 14. Enum mapping with custom Type example
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@Type(GenderType.class)
	@Column(length = 6)
	public Gender gender;

	//Getters and setters are omitted for brevity

}

public class GenderType extends UserTypeSupport<Gender> {
    public GenderType() {
        super(Gender.class, Types.CHAR);
    }
}

public class GenderJavaType extends AbstractClassJavaType<Gender> {

    public static final GenderJavaType INSTANCE =
        new GenderJavaType();

    protected GenderJavaType() {
        super(Gender.class);
    }

    public String toString(Gender value) {
        return value == null ? null : value.name();
    }

    public Gender fromString(CharSequence string) {
        return string == null ? null : Gender.valueOf(string.toString());
    }

    public <X> X unwrap(Gender value, Class<X> type, WrapperOptions options) {
        return CharacterJavaType.INSTANCE.unwrap(
            value == null ? null : value.getCode(),
            type,
            options
       );
    }

    public <X> Gender wrap(X value, WrapperOptions options) {
        return Gender.fromCode(
				CharacterJavaType.INSTANCE.wrap( value, options)
       );
    }
}

Again, the gender column is defined as a CHAR type and would hold:

NULL

For null values

'M'

For the MALE enum

'F'

For the FEMALE enum

For additional details on using custom types, see Custom type mapping section.

3.2.6. Boolean

By default, Boolean attributes map to BOOLEAN columns, at least when the database has a dedicated BOOLEAN type. On databases which don’t, Hibernate uses whatever else is available: BIT, TINYINT, or SMALLINT.

Example 15. Implicit boolean mapping
// this will be mapped to BIT or BOOLEAN on the database
@Basic
boolean implicit;

However, it is quite common to find boolean values encoded as a character or as an integer. Such cases are exactly the intention of AttributeConverter. For convenience, Hibernate provides 3 built-in converters for the common boolean mapping cases:

  • YesNoConverter encodes a boolean value as 'Y' or 'N',

  • TrueFalseConverter encodes a boolean value as 'T' or 'F', and

  • NumericBooleanConverter encodes the value as an integer, 1 for true, and 0 for false.

Example 16. Using AttributeConverter
// this will get mapped to CHAR or NCHAR with a conversion
@Basic
@Convert(converter = org.hibernate.type.YesNoConverter.class)
boolean convertedYesNo;

// this will get mapped to CHAR or NCHAR with a conversion
@Basic
@Convert(converter = org.hibernate.type.TrueFalseConverter.class)
boolean convertedTrueFalse;

// this will get mapped to TINYINT with a conversion
@Basic
@Convert(converter = org.hibernate.type.NumericBooleanConverter.class)
boolean convertedNumeric;

If the boolean value is defined in the database as something other than BOOLEAN, character or integer, the value can also be mapped using a custom AttributeConverter - see AttributeConverters.

A UserType may also be used - see Custom type mapping

3.2.7. Byte

By default, Hibernate maps values of Byte / byte to the TINYINT JDBC type.

Example 17. Mapping Byte
// these will both be mapped using TINYINT
Byte wrapper;
byte primitive;

See Byte array for mapping arrays of bytes.

3.2.8. Short

By default, Hibernate maps values of Short / short to the SMALLINT JDBC type.

Example 18. Mapping Short
// these will both be mapped using SMALLINT
Short wrapper;
short primitive;

3.2.9. Integer

By default, Hibernate maps values of Integer / int to the INTEGER JDBC type.

Example 19. Mapping Integer
// these will both be mapped using INTEGER
Integer wrapper;
int primitive;

3.2.10. Long

By default, Hibernate maps values of Long / long to the BIGINT JDBC type.

Example 20. Mapping Long
// these will both be mapped using BIGINT
Long wrapper;
long primitive;

3.2.11. BigInteger

By default, Hibernate maps values of BigInteger to the NUMERIC JDBC type.

Example 21. Mapping BigInteger
// will be mapped using NUMERIC
BigInteger wrapper;

3.2.12. Double

By default, Hibernate maps values of Double to the DOUBLE, FLOAT, REAL or NUMERIC JDBC type depending on the capabilities of the database

Example 22. Mapping Double
// these will be mapped using DOUBLE, FLOAT, REAL or NUMERIC
// depending on the capabilities of the database
Double wrapper;
double primitive;

A specific type can be influenced using any of the JDBC type influencers covered in JdbcType section.

If @JdbcTypeCode is used, the Dialect is still consulted to make sure the database supports the requested type. If not, an appropriate type is selected

3.2.13. Float

By default, Hibernate maps values of Float to the FLOAT, REAL or NUMERIC JDBC type depending on the capabilities of the database.

Example 23. Mapping Float
// these will be mapped using FLOAT, REAL or NUMERIC
// depending on the capabilities of the database
Float wrapper;
float primitive;

A specific type can be influenced using any of the JDBC type influencers covered in Mapping basic values section.

If @JdbcTypeCode is used, the Dialect is still consulted to make sure the database supports the requested type. If not, an appropriate type is selected

3.2.14. BigDecimal

By default, Hibernate maps values of BigDecimal to the NUMERIC JDBC type.

Example 24. Mapping BigDecimal
// will be mapped using NUMERIC
BigDecimal wrapper;

3.2.15. Character

By default, Hibernate maps Character to the CHAR JDBC type.

Example 25. Mapping Character
// these will be mapped using CHAR
Character wrapper;
char primitive;

3.2.16. String

By default, Hibernate maps String to the VARCHAR JDBC type.

Example 26. Mapping String
// will be mapped using VARCHAR
String string;

// will be mapped using CLOB
@Lob
String clobString;

Optionally, you may specify the maximum length of the string using @Column(length=…​), or using the @Size annotation from Hibernate Validator. For very large strings, you can use one of the constant values defined by the class org.hibernate.Length, for example:

@Column(length=Length.LONG)
private String text;

Alternatively, you may explicitly specify the JDBC type LONGVARCHAR, which is treated as a VARCHAR mapping with default length=Length.LONG when no length is explicitly specified:

@JdbcTypeCode(Types.LONGVARCHAR)
private String text;

If you use Hibernate for schema generation, Hibernate will generate DDL with a column type that is large enough to accommodate the maximum length you’ve specified.

If the maximum length you specify is too long to fit in the largest VARCHAR column supported by your database, Hibernate’s schema exporter will automatically upgrade the column type to TEXT, CLOB, or whatever is the equivalent type for your database. Please don’t (ab)use JPA’s @Lob annotation just because you want a TEXT column. The purpose of the @Lob annotation is not to control DDL generation!

See Handling LOB data for details on mapping to a database CLOB.

For databases which support nationalized character sets, you can also store strings as nationalized data.

Example 27. Mapping String as nationalized
// will be mapped using NVARCHAR
@Nationalized
String nstring;

// will be mapped using NCLOB
@Lob
@Nationalized
String nclobString;

See Handling nationalized character data for details on mapping strings using nationalized character sets.

3.2.17. Character arrays

By default, Hibernate maps char[] to the VARCHAR JDBC type. Since Character[] can contain null elements, it is mapped as basic array type instead. Prior to Hibernate 6.2, also Character[] mapped to VARCHAR, yet disallowed null elements. To continue mapping Character[] to the VARCHAR JDBC type, or for LOBs mapping to the CLOB JDBC type, it is necessary to annotate the persistent attribute with @JavaType( CharacterArrayJavaType.class ).

Example 28. Mapping Character
// mapped as VARCHAR
char[] primitive;
Character[] wrapper;
@JavaType( CharacterArrayJavaType.class )
Character[] wrapperOld;

// mapped as CLOB
@Lob
char[] primitiveClob;
@Lob
Character[] wrapperClob;

See Handling LOB data for details on mapping as database LOB.

For databases which support nationalized character sets, you can also store character arrays as nationalized data.

Example 29. Mapping character arrays as nationalized
// mapped as NVARCHAR
@Nationalized
char[] primitiveNVarchar;
@Nationalized
Character[] wrapperNVarchar;
@Nationalized
@JavaType( CharacterArrayJavaType.class )
Character[] wrapperNVarcharOld;

// mapped as NCLOB
@Lob
@Nationalized
char[] primitiveNClob;
@Lob
@Nationalized
Character[] wrapperNClob;

See Handling nationalized character data for details on mapping strings using nationalized character sets.

3.2.18. Clob / NClob

Be sure to check out Handling LOB data which covers basics of LOB handling and Handling nationalized character data which covers basics of nationalized data handling.

By default, Hibernate will map the java.sql.Clob Java type to CLOB and java.sql.NClob to NCLOB.

Considering we have the following database table:

Example 30. CLOB - SQL
CREATE TABLE Product (
  id INTEGER NOT NULL,
  name VARCHAR(255),
  warranty CLOB,
  PRIMARY KEY (id)
)

Let’s first map this using the @Lob Jakarta Persistence annotation and the java.sql.Clob type:

Example 31. CLOB mapped to java.sql.Clob
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    private Clob warranty;

    //Getters and setters are omitted for brevity

}

To persist such an entity, you have to create a Clob using the ClobProxy Hibernate utility:

Example 32. Persisting a java.sql.Clob entity
String warranty = "My product warranty";

final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");

product.setWarranty(ClobProxy.generateProxy(warranty));

entityManager.persist(product);

To retrieve the Clob content, you need to transform the underlying java.io.Reader:

Example 33. Returning a java.sql.Clob entity
Product product = entityManager.find(Product.class, productId);

try (Reader reader = product.getWarranty().getCharacterStream()) {
    assertEquals("My product warranty", toString(reader));
}

We could also map the CLOB in a materialized form. This way, we can either use a String or a char[].

Example 34. CLOB mapped to String
@Entity(name = "Product")
public static class Product {

	@Id
	private Integer id;

	private String name;

	@Lob
	private String warranty;

	//Getters and setters are omitted for brevity

}

We might even want the materialized data as a char array.

Example 35. CLOB - materialized char[] mapping
@Entity(name = "Product")
public static class Product {

	@Id
	private Integer id;

	private String name;

	@Lob
	private char[] warranty;

	//Getters and setters are omitted for brevity

}

Just like with CLOB, Hibernate can also deal with NCLOB SQL data types:

Example 36. NCLOB - SQL
CREATE TABLE Product (
    id INTEGER NOT NULL ,
    name VARCHAR(255) ,
    warranty nclob ,
    PRIMARY KEY ( id )
)

Hibernate can map the NCLOB to a java.sql.NClob

Example 37. NCLOB mapped to java.sql.NClob
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    @Nationalized
    // Clob also works, because NClob extends Clob.
    // The database type is still NCLOB either way and handled as such.
    private NClob warranty;

    //Getters and setters are omitted for brevity

}

To persist such an entity, you have to create an NClob using the NClobProxy Hibernate utility:

Example 38. Persisting a java.sql.NClob entity
String warranty = "My product warranty";

final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");

product.setWarranty(NClobProxy.generateProxy(warranty));

entityManager.persist(product);

To retrieve the NClob content, you need to transform the underlying java.io.Reader:

Example 39. Returning a java.sql.NClob entity
Product product = entityManager.find(Product.class, 1);

try (Reader reader = product.getWarranty().getCharacterStream()) {
    assertEquals("My product warranty", toString(reader));
}

We could also map the NCLOB in a materialized form. This way, we can either use a String or a char[].

Example 40. NCLOB mapped to String
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    @Nationalized
    private String warranty;

    //Getters and setters are omitted for brevity

}

We might even want the materialized data as a char array.

Example 41. NCLOB - materialized char[] mapping
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    @Nationalized
    private char[] warranty;

    //Getters and setters are omitted for brevity

}

3.2.19. Byte array

By default, Hibernate maps byte[] to the VARBINARY JDBC type. Since Byte[] can contain null elements, it is mapped as basic array type instead. Prior to Hibernate 6.2, also Byte[] mapped to VARBINARY, yet disallowed null elements. To continue mapping Byte[] to the VARBINARY JDBC type, or for LOBs mapping to the BLOB JDBC type, it is necessary to annotate the persistent attribute with @JavaType( ByteArrayJavaType.class ).

Example 42. Mapping arrays of bytes
// mapped as VARBINARY
private byte[] primitive;
private Byte[] wrapper;
@JavaType( ByteArrayJavaType.class )
private Byte[] wrapperOld;

// mapped as (materialized) BLOB
@Lob
private byte[] primitiveLob;
@Lob
private Byte[] wrapperLob;

Just like with strings, you may specify the maximum length using @Column(length=…​) or the @Size annotation from Hibernate Validator. For very large arrays, you can use the constants defined by org.hibernate.Length. Alternatively @JdbcTypeCode(Types.LONGVARBINARY) is treated as a VARBINARY mapping with default length=Length.LONG when no length is explicitly specified.

If you use Hibernate for schema generation, Hibernate will generate DDL with a column type that is large enough to accommodate the maximum length you’ve specified.

If the maximum length you specify is too long to fit in the largest VARBINARY column supported by your database, Hibernate’s schema exporter will automatically upgrade the column type to IMAGE, BLOB, or whatever is the equivalent type for your database. Please don’t (ab)use JPA’s @Lob annotation for DDL customization.

See Handling LOB data for details on mapping to a database BLOB.

3.2.20. Blob

Be sure to check out Handling LOB data which covers basics of LOB handling.

By default, Hibernate will map the java.sql.Blob Java type to BLOB.

Considering we have the following database table:

Example 43. BLOB - SQL
CREATE TABLE Product (
    id INTEGER NOT NULL ,
    image blob ,
    name VARCHAR(255) ,
    PRIMARY KEY ( id )
)

Let’s first map this using the JDBC java.sql.Blob type.

Example 44. BLOB mapped to java.sql.Blob
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    private Blob image;

    //Getters and setters are omitted for brevity

}

To persist such an entity, you have to create a Blob using the BlobProxy Hibernate utility:

Example 45. Persisting a java.sql.Blob entity
byte[] image = new byte[] {1, 2, 3};

final Product product = new Product();
product.setId(1);
product.setName("Mobile phone");

product.setImage(BlobProxy.generateProxy(image));

entityManager.persist(product);

To retrieve the Blob content, you need to transform the underlying java.io.InputStream:

Example 46. Returning a java.sql.Blob entity
Product product = entityManager.find(Product.class, productId);

try (InputStream inputStream = product.getImage().getBinaryStream()) {
    assertArrayEquals(new byte[] {1, 2, 3}, toBytes(inputStream));
}

We could also map the BLOB in a materialized form (e.g. byte[]).

Example 47. BLOB mapped to byte[]
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Lob
    private byte[] image;

    //Getters and setters are omitted for brevity

}

3.2.21. Duration

By default, Hibernate maps Duration to the NUMERIC SQL type.

It’s possible to map Duration to the INTERVAL_SECOND SQL type using @JdbcTypeCode(INTERVAL_SECOND) or by setting hibernate.type.preferred_duration_jdbc_type=INTERVAL_SECOND
Example 48. Mapping Duration
private Duration duration;

3.2.22. Instant

Instant is mapped to the TIMESTAMP_UTC SQL type.

Example 49. Mapping Instant
// mapped as TIMESTAMP
private Instant instant;

See Handling temporal data for basics of temporal mapping

3.2.23. LocalDate

LocalDate is mapped to the DATE JDBC type.

Example 50. Mapping LocalDate
// mapped as DATE
private LocalDate localDate;

See Handling temporal data for basics of temporal mapping

3.2.24. LocalDateTime

LocalDateTime is mapped to the TIMESTAMP JDBC type.

Example 51. Mapping LocalDateTime
// mapped as TIMESTAMP
private LocalDateTime localDateTime;

See Handling temporal data for basics of temporal mapping

3.2.25. LocalTime

LocalTime is mapped to the TIME JDBC type.

Example 52. Mapping LocalTime
// mapped as TIME
private LocalTime localTime;

See Handling temporal data for basics of temporal mapping

3.2.26. OffsetDateTime

OffsetDateTime is mapped to the TIMESTAMP or TIMESTAMP_WITH_TIMEZONE JDBC type depending on the database.

Example 53. Mapping OffsetDateTime
// mapped as TIMESTAMP or TIMESTAMP_WITH_TIMEZONE
private OffsetDateTime offsetDateTime;

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.27. OffsetTime

OffsetTime is mapped to the TIME or TIME_WITH_TIMEZONE JDBC type depending on the database.

Example 54. Mapping OffsetTime
// mapped as TIME or TIME_WITH_TIMEZONE
private OffsetTime offsetTime;

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.28. TimeZone

TimeZone is mapped to VARCHAR JDBC type.

Example 55. Mapping OffsetTime
// mapped as VARCHAR
private TimeZone timeZone;

3.2.29. ZonedDateTime

ZonedDateTime is mapped to the TIMESTAMP or TIMESTAMP_WITH_TIMEZONE JDBC type depending on the database.

Example 56. Mapping ZonedDateTime
// mapped as TIMESTAMP or TIMESTAMP_WITH_TIMEZONE
private ZonedDateTime zonedDateTime;

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.30. ZoneOffset

ZoneOffset is mapped to VARCHAR JDBC type.

Example 57. Mapping ZoneOffset
// mapped as VARCHAR
private ZoneOffset zoneOffset;

3.2.31. Calendar

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.32. Date

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.33. Time

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.34. Timestamp

See Handling temporal data for basics of temporal mapping See Using a specific time zone for basics of time-zone handling

3.2.35. Class

Hibernate maps Class references to VARCHAR JDBC type

Example 58. Mapping Class
// mapped as VARCHAR
private Class<?> clazz;

3.2.36. Currency

Hibernate maps Currency references to VARCHAR JDBC type

Example 59. Mapping Currency
// mapped as VARCHAR
private Currency currency;

3.2.37. Locale

Hibernate maps Locale references to VARCHAR JDBC type

Example 60. Mapping Locale
// mapped as VARCHAR
private Locale locale;

3.2.38. UUID

Hibernate allows mapping UUID values in a number of ways. By default, Hibernate will store UUID values in the native form by using the SQL type UUID or in binary form with the BINARY JDBC type if the database does not have a native UUID type.

The default uses the binary representation because it uses a more efficient column storage.

However, many applications prefer the readability of the character-based column storage.

To switch the default mapping, set the hibernate.type.preferred_uuid_jdbc_type configuration to CHAR.

UUID as binary

As mentioned, the default mapping for UUID attributes. Maps the UUID to a byte[] using java.util.UUID#getMostSignificantBits and java.util.UUID#getLeastSignificantBits and stores that as BINARY data.

Chosen as the default simply because it is generally more efficient from a storage perspective.

UUID as (var)char

Maps the UUID to a String using java.util.UUID#toString and java.util.UUID#fromString and stores that as CHAR or VARCHAR data.

UUID as identifier

Hibernate supports using UUID values as identifiers, and they can even be generated on the user’s behalf. For details, see the discussion of generators in Identifiers.

3.2.39. InetAddress

By default, Hibernate will map InetAddress to the INET SQL type and fallback to BINARY if necessary.

Example 61. Mapping InetAddress
private InetAddress address;

3.2.40. JSON mapping

Hibernate will only use the JSON type if explicitly configured through @JdbcTypeCode( SqlTypes.JSON ). The JSON library used for serialization/deserialization is detected automatically, but can be overridden by setting hibernate.type.json_format_mapper as can be read in the Configurations section.

Example 62. Mapping JSON
@JdbcTypeCode( SqlTypes.JSON )
private Map<String, String> stringMap;

3.2.41. XML mapping

Hibernate will only use the XML type if explicitly configured through @JdbcTypeCode( SqlTypes.SQLXML ). The XML library used for serialization/deserialization is detected automatically, but can be overridden by setting hibernate.type.xml_format_mapper as can be read in the Configurations section.

Example 63. Mapping XML
@JdbcTypeCode( SqlTypes.SQLXML )
private Map<String, StringNode> stringMap;

3.2.42. Basic array mapping

Basic arrays, other than byte[]/Byte[] and char[]/Character[], map to the type code SqlTypes.ARRAY by default, which maps to the SQL standard array type if possible, as determined via the new methods getArrayTypeName and supportsStandardArrays of org.hibernate.dialect.Dialect. If SQL standard array types are not available, data will be modeled as SqlTypes.JSON, SqlTypes.XML or SqlTypes.VARBINARY, depending on the database support as determined via the new method org.hibernate.dialect.Dialect.getPreferredSqlTypeCodeForArray.

Example 64. Mapping basic arrays
Short[] wrapper;
short[] primitive;

3.2.43. Basic collection mapping

Basic collections (only subtypes of Collection), which are not annotated with @ElementCollection, map to the type code SqlTypes.ARRAY by default, which maps to the SQL standard array type if possible, as determined via the new methods getArrayTypeName and supportsStandardArrays of org.hibernate.dialect.Dialect. If SQL standard array types are not available, data will be modeled as SqlTypes.JSON, SqlTypes.XML or SqlTypes.VARBINARY, depending on the database support as determined via the new method org.hibernate.dialect.Dialect.getPreferredSqlTypeCodeForArray.

Example 65. Mapping basic collections
List<Short> list;
SortedSet<Short> sortedSet;

3.2.44. Compositional basic mapping

The compositional approach allows defining how the mapping should work in terms of influencing individual parts that make up a basic-value mapping. This section will look at these individual parts and the specifics of influencing each.

JavaType

Hibernate needs to understand certain aspects of the Java type to handle values properly and efficiently. Hibernate understands these capabilities through its org.hibernate.type.descriptor.java.JavaType contract. Hibernate provides built-in support for many JDK types (Integer, String, e.g.), but also supports the ability for the application to change the handling for any of the standard JavaType registrations as well as add in handling for non-standard types. Hibernate provides multiple ways for the application to influence the JavaType descriptor to use.

The resolution can be influenced locally using the @JavaType annotation on a particular mapping. The indicated descriptor will be used just for that mapping. There are also forms of @JavaType for influencing the keys of a Map (@MapKeyJavaType), the index of a List or array (@ListIndexJavaType), the identifier of an ID-BAG mapping (@CollectionIdJavaType) as well as the discriminator (@AnyDiscriminator) and key (@AnyKeyJavaClass, @AnyKeyJavaType) of an ANY mapping.

The resolution can also be influenced globally by registering the appropriate JavaType descriptor with the JavaTypeRegistry. This approach is able to both "override" the handling for certain Java types or to register new types. See Registries for discussion of JavaTypeRegistry.

See Resolving the composition for a discussion of the process used to resolve the mapping composition.

JdbcType

Hibernate also needs to understand aspects of the JDBC type it should use (how it should bind values, how it should extract values, etc.) which is the role of its org.hibernate.type.descriptor.jdbc.JdbcType contract. Hibernate provides multiple ways for the application to influence the JdbcType descriptor to use.

Locally, the resolution can be influenced using either the @JdbcType or @JdbcTypeCode annotations. There are also annotations for influencing the JdbcType in relation to Map keys (@MapKeyJdbcType, @MapKeyJdbcTypeCode), the index of a List or array (@ListIndexJdbcType, @ListIndexJdbcTypeCode), the identifier of an ID-BAG mapping (@CollectionIdJdbcType, @CollectionIdJdbcTypeCode) as well as the key of an ANY mapping (@AnyKeyJdbcType, @AnyKeyJdbcTypeCode). The @JdbcType specifies a specific JdbcType implementation to use while @JdbcTypeCode specifies a "code" that is then resolved against the JdbcTypeRegistry.

The "type code" relative to a JdbcType generally maps to the corresponding value in java.sql.Types. registers entries in the JdbcTypeRegistry for all the standard java.sql.Types codes (aside from OTHER, which is special). See Registries for more discussion.

Customizing the JdbcTypeRegistry can be accomplished through @JdbcTypeRegistration and TypeContributor. See Registries for discussion of JavaTypeRegistry. See TypeContributor for discussion of TypeContributor.

See the @JdbcTypeCode Javadoc for details.

See Resolving the composition for a discussion of the process used to resolve the mapping composition.

MutabilityPlan

MutabilityPlan is the means by which Hibernate understands how to deal with the domain value in terms of its internal mutability as well as related concerns such as making copies. While it seems like a minor concern, it can have a major impact on performance. See AttributeConverter Mutability Plan for one case where this can manifest. See also Case Study : BitSet for another discussion.

The MutabilityPlan for a mapping can be influenced by any of the following annotations:

  • @Mutability

  • @Immutable

  • @MapKeyMutability

  • @CollectionIdMutability

Hibernate checks the following places for @Mutability and @Immutable, in order of precedence:

  1. Local to the mapping

  2. On the associated AttributeConverter implementation class (if one)

  3. On the value’s Java type

In most cases, the fallback defined by JavaType#getMutabilityPlan is the proper strategy.

Hibernate uses MutabilityPlan to:

  1. Check whether a value is considered dirty

  2. Make deep copies

  3. Marshal values to and from the second-level cache

Generally speaking, immutable values perform better in all of these cases

  1. To check for dirtiness, Hibernate just needs to check object identity (==) as opposed to equality (Object#equals).

  2. The same value instance can be used as the deep copy of itself.

  3. The same value can be used from the second-level cache as well as the value we put into the second-level cache.

If a particular Java type is considered mutable (a Date e.g.), @Immutable or a immutable-specific MutabilityPlan implementation can be specified to have Hibernate treat the value as immutable. This also acts as a contract from the application that the internal state of these objects is not changed by the application. Specifying that a mutable type is immutable and then changing the internal state will lead to problems; so only do this if the application unequivocally does not change the internal state.

See Resolving the composition for a discussion of the process used to resolve the mapping composition.

BasicValueConverter

BasicValueConverter is roughly analogous to AttributeConverter in that it describes a conversion to happen when reading or writing values of a basic-valued model part. In fact, internally Hibernate wraps an applied AttributeConverter in a BasicValueConverter. It also applies implicit BasicValueConverter converters in certain cases such as enum handling, etc.

Hibernate does not provide an explicit facility to influence these conversions beyond AttributeConverter. See AttributeConverters.

See Resolving the composition for a discussion of the process used to resolve the mapping composition.

Resolving the composition

Using this composition approach, Hibernate will need to resolve certain parts of this mapping. Often this involves "filling in the blanks" as it will be configured for just parts of the mapping. This section outlines how this resolution happens.

This is a complicated process and is only covered at a high level for the most common cases here.

For the full specifics, consult the source code for org.hibernate.mapping.BasicValue#buildResolution

First, we look for a custom type. If found, this takes predence. See Custom type mapping for details

If an AttributeConverter is applied, we use it as the basis for the resolution

  1. If @JavaType is also used, that specific JavaType is used for the converter’s "domain type". Otherwise, the Java type defined by the converter as its "domain type" is resolved against the JavaTypeRegistry

  2. If @JdbcType or @JdbcTypeCode is used, the indicated JdbcType is used and the converted "relational Java type" is determined by JdbcType#getJdbcRecommendedJavaTypeMapping. Otherwise, the Java type defined by the converter as its relational type is used and the JdbcType is determined by JdbcType#getRecommendedJdbcType

  3. The MutabilityPlan can be specified using @Mutability or @Immutable on the AttributeConverter implementation, the basic value mapping or the Java type used as the domain-type. Otherwise, JdbcType#getJdbcRecommendedJavaTypeMapping for the conversion’s domain-type is used to determine the mutability-plan.

Next we try to resolve the JavaType to use for the mapping. We check for an explicit @JavaType and use the specified JavaType if found. Next any "implicit" indication is checked; for example, the index for a List has the implicit Java type of Integer. Next, we use reflection if possible. If we are unable to determine the JavaType to use through the preceeding steps, we try to resolve an explicitly specified JdbcType to use and, if found, use its JdbcType#getJdbcRecommendedJavaTypeMapping as the mapping’s JavaType. If we are not able to determine the JavaType by this point, an error is thrown.

The JavaType resolved earlier is then inspected for a number of special cases.

  1. For enum values, we check for an explicit @Enumerated and create an enumeration mapping. Note that this resolution still uses any explicit JdbcType indicators

  2. For temporal values, we check for @Temporal and create an enumeration mapping. Note that this resolution still uses any explicit JdbcType indicators; this includes @JdbcType and @JdbcTypeCode, as well as @TimeZoneStorage and @TimeZoneColumn if appropriate.

The fallback at this point is to use the JavaType and JdbcType determined in earlier steps to create a JDBC-mapping (which encapsulates the JavaType and JdbcType) and combines it with the resolved MutabilityPlan

When using the compositional approach, there are other ways to influence the resolution as covered in Enums, Handling temporal data, Handling LOB data and Handling nationalized character data

See TypeContributor for an alternative to @JavaTypeRegistration and @JdbcTypeRegistration.

3.2.45. Custom type mapping

Another approach is to supply the implementation of the org.hibernate.usertype.UserType contract using @Type.

There are also corresponding, specialized forms of @Type for specific model parts:

  • When mapping a Map, @Type describes the Map value while @MapKeyType describe the Map key

  • When mapping an id-bag, @Type describes the elements while @CollectionIdType describes the collection-id

  • For other collection mappings, @Type describes the elements

  • For discriminated association mappings (@Any and @ManyToAny), @Type describes the discriminator value

@Type allows for more complex mapping concerns; but, AttributeConverter and Compositional basic mapping should generally be preferred as simpler solutions

3.2.46. Handling nationalized character data

How nationalized character data is handled and stored depends on the underlying database.

Most databases support storing nationalized character data through the standardized SQL NCHAR, NVARCHAR, LONGNVARCHAR and NCLOB variants.

Others support storing nationalized data as part of CHAR, VARCHAR, LONGVARCHAR and CLOB. Generally these databases do not support NCHAR, NVARCHAR, LONGNVARCHAR and NCLOB, even as aliased types.

Ultimately Hibernate understands this through Dialect#getNationalizationSupport()

To ensure nationalized character data gets stored and accessed correctly, @Nationalized can be used locally or hibernate.use_nationalized_character_data can be set globally.

@Nationalized and hibernate.use_nationalized_character_data can be used regardless of the specific database support for nationalized data and allows the application to work portably across databases with varying support.

For databases with no NCLOB data type, attributes of type java.sql.NClob are simply unsupported. Use java.sql.Clob (which NClob extends) or a materialized mapping like String or char[] instead.

See also Handling LOB data regarding similar limitation for databases which do not support explicit CLOB data-type.

Considering we have the following database table:

Example 66. NVARCHAR - SQL
CREATE TABLE Product (
    id INTEGER NOT NULL ,
    name VARCHAR(255) ,
    warranty NVARCHAR(255) ,
    PRIMARY KEY ( id )
)

To map a specific attribute to a nationalized variant data type, Hibernate defines the @Nationalized annotation.

Example 67. NVARCHAR mapping
@Entity(name = "Product")
public static class Product {

    @Id
    private Integer id;

    private String name;

    @Nationalized
    private String warranty;

    //Getters and setters are omitted for brevity

}

3.2.47. Handling LOB data

The @Lob annotation specifies that character or binary data should be written to the database using the special JDBC APIs for handling database LOB (Large OBject) types.

How JDBC deals with LOB data varies from driver to driver. Hibernate tries to take care of all these differences, and protect you as much as possible from inconsistent driver behavior. Sadly, Hibernate is only partially successful at achieving this goal.

Some database drivers (i.e. PostgreSQL) are especially problematic and in such cases you might have to do some extra work to get LOBs functioning. But that’s beyond the scope of this guide.

For databases with no CLOB type, attributes of type java.sql.Clob are simply unsupported. Use a materialized type like String or char[] instead.

There’s two ways a LOB may be represented in the Java domain model:

  • using a special JDBC-defined LOB locator type, or

  • using a regular "materialized" type like String, char[], or byte[].

LOB Locator

The JDBC LOB locator types are:

  • java.sql.Blob

  • java.sql.Clob

  • java.sql.NClob

These types represent references to off-table LOB data. In principle, they allow JDBC drivers to support more efficient access to the LOB data. Some drivers stream parts of the LOB data as needed, potentially consuming less memory.

However, java.sql.Blob and java.sql.Clob can be unnatural to deal with and suffer certain limitations. For example, it’s not portable to access a LOB locator after the end of the transaction in which it was obtained.

Materialized LOB

Alternatively, Hibernate lets you access LOB data via the familiar Java types String, char[], and byte[]. But of course this requires materializing the entire contents of the LOB in memory when the object is first retrieved. Whether this performance cost is acceptable depends on many factors, including the vagaries of the JDBC driver.

You don’t need to use a @Lob mapping for every database column of type BLOB or CLOB. The @Lob annotation is a special-purpose tool that should only be used when a default basic mapping to String would result in unacceptable performance characteristics.

3.2.48. Handling temporal data

Hibernate supports mapping temporal values in numerous ways, though ultimately these strategies boil down to the 3 main Date/Time types defined by the SQL specification:

DATE

Represents a calendar date by storing years, months and days.

TIME

Represents the time of a day by storing hours, minutes and seconds.

TIMESTAMP

Represents both a DATE and a TIME plus nanoseconds.

TIMESTAMP WITH TIME ZONE

Represents both a DATE and a TIME plus nanoseconds and zone id or offset.

The mapping of java.time temporal types to the specific SQL Date/Time types is implied as follows:

DATE

java.time.LocalDate

TIME

java.time.LocalTime, java.time.OffsetTime

TIMESTAMP

java.time.Instant, java.time.LocalDateTime, java.time.OffsetDateTime and java.time.ZonedDateTime

TIMESTAMP WITH TIME ZONE

java.time.OffsetDateTime, java.time.ZonedDateTime

Although Hibernate recommends the use of the java.time package for representing temporal values, it does support using java.sql.Date, java.sql.Time, java.sql.Timestamp, java.util.Date and java.util.Calendar.

The mappings for java.sql.Date, java.sql.Time, java.sql.Timestamp are implicit:

DATE

java.sql.Date

TIME

java.sql.Time

TIMESTAMP

java.sql.Timestamp

Applying @Temporal to java.sql.Date, java.sql.Time, java.sql.Timestamp or any of the java.time types is considered an exception

When using java.util.Date or java.util.Calendar, Hibernate assumes TIMESTAMP. To alter that, use @Temporal.

Example 68. Mapping java.util.Date
// mapped as TIMESTAMP by default
Date dateAsTimestamp;

// explicitly mapped as DATE
@Temporal(TemporalType.DATE)
Date dateAsDate;

// explicitly mapped as TIME
@Temporal(TemporalType.TIME)
Date dateAsTime;
Using a specific time zone

By default, Hibernate is going to use the PreparedStatement.setTimestamp(int parameterIndex, java.sql.Timestamp) or PreparedStatement.setTime(int parameterIndex, java.sql.Time x) when saving a java.sql.Timestamp or a java.sql.Time property.

When the time zone is not specified, the JDBC driver is going to use the underlying JVM default time zone, which might not be suitable if the application is used from all across the globe. For this reason, it is very common to use a single reference time zone (e.g. UTC) whenever saving/loading data from the database.

One alternative would be to configure all JVMs to use the reference time zone:

Declaratively
java -Duser.timezone=UTC ...
Programmatically
TimeZone.setDefault( TimeZone.getTimeZone( "UTC" ) );

However, as explained in this article, this is not always practical, especially for front-end nodes. For this reason, Hibernate offers the hibernate.jdbc.time_zone configuration property which can be configured:

Declaratively, at the SessionFactory level
settings.put(
    AvailableSettings.JDBC_TIME_ZONE,
    TimeZone.getTimeZone( "UTC" )
);
Programmatically, on a per Session basis
Session session = sessionFactory()
    .withOptions()
    .jdbcTimeZone( TimeZone.getTimeZone( "UTC" ) )
    .openSession();

With this configuration property in place, Hibernate is going to call the PreparedStatement.setTimestamp(int parameterIndex, java.sql.Timestamp, Calendar cal) or PreparedStatement.setTime(int parameterIndex, java.sql.Time x, Calendar cal), where the java.util.Calendar references the time zone provided via the hibernate.jdbc.time_zone property.

Handling time zoned temporal data

By default, Hibernate will convert and normalize OffsetDateTime and ZonedDateTime to java.sql.Timestamp in UTC. This behavior can be altered by configuring the hibernate.timezone.default_storage property

settings.put(
    AvailableSettings.TIMEZONE_DEFAULT_STORAGE,
    TimeZoneStorageType.AUTO
);

Other possible storage types are AUTO, COLUMN, NATIVE and NORMALIZE (the default). With COLUMN, Hibernate will save the time zone information into a dedicated column, whereas NATIVE will require the support of database for a TIMESTAMP WITH TIME ZONE data type that retains the time zone information. NORMALIZE doesn’t store time zone information and will simply convert the timestamp to UTC. Hibernate understands what a database/dialect supports through Dialect#getTimeZoneSupport and will abort with a boot error if the NATIVE is used in conjunction with a database that doesn’t support this. For AUTO, Hibernate tries to use NATIVE if possible and falls back to COLUMN otherwise.

3.2.49. @TimeZoneStorage

Hibernate supports defining the storage to use for time zone information for individual properties via the @TimeZoneStorage and @TimeZoneColumn annotations. The storage type can be specified via the @TimeZoneStorage by specifying a org.hibernate.annotations.TimeZoneStorageType. The default storage type is AUTO which will ensure that the time zone information is retained. The @TimeZoneColumn annotation can be used in conjunction with AUTO or COLUMN and allows to define the column details for the time zone information storage.

Storing the zone offset might be problematic for future timestamps as zone rules can change. Due to this, storing the offset is only safe for past timestamps, and we advise sticking to the NORMALIZE strategy by default.

Example 69. @TimeZoneColumn usage
@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthtime_offset_offset")
@Column(name = "birthtime_offset")
private OffsetTime offsetTimeColumn;

@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthday_offset_offset")
@Column(name = "birthday_offset")
private OffsetDateTime offsetDateTimeColumn;

@TimeZoneStorage(TimeZoneStorageType.COLUMN)
@TimeZoneColumn(name = "birthday_zoned_offset")
@Column(name = "birthday_zoned")
private ZonedDateTime zonedDateTimeColumn;

3.2.50. AttributeConverters

With a custom AttributeConverter, the application developer can map a given JDBC type to an entity basic type.

In the following example, the java.time.Period is going to be mapped to a VARCHAR database column.

Example 70. java.time.Period custom AttributeConverter
@Converter
public class PeriodStringConverter
        implements AttributeConverter<Period, String> {

    @Override
    public String convertToDatabaseColumn(Period attribute) {
        return attribute.toString();
    }

    @Override
    public Period convertToEntityAttribute(String dbData) {
        return Period.parse(dbData);
    }
}

To make use of this custom converter, the @Convert annotation must decorate the entity attribute.

Example 71. Entity using the custom java.time.Period AttributeConverter mapping
@Entity(name = "Event")
public static class Event {

    @Id
    @GeneratedValue
    private Long id;

    @Convert(converter = PeriodStringConverter.class)
    @Column(columnDefinition = "")
    private Period span;

    //Getters and setters are omitted for brevity

}

When persisting such entity, Hibernate will do the type conversion based on the AttributeConverter logic:

Example 72. Persisting entity using the custom AttributeConverter
INSERT INTO Event ( span, id )
VALUES ( 'P1Y2M3D', 1 )

An AttributeConverter can be applied globally for (@Converter( autoApply=true )) or locally.

AttributeConverter Java and JDBC types

In cases when the Java type specified for the "database side" of the conversion (the second AttributeConverter bind parameter) is not known, Hibernate will fallback to a java.io.Serializable type.

If the Java type is not known to Hibernate, you will encounter the following message:

HHH000481: Encountered Java type for which we could not locate a JavaType and which does not appear to implement equals and/or hashCode. This can lead to significant performance problems when performing equality/dirty checking involving this Java type. Consider registering a custom JavaType or at least implementing equals/hashCode.

A Java type is "known" if it has an entry in the JavaTypeRegistry. While Hibernate does load many JDK types into the JavaTypeRegistry, an application can also expand the JavaTypeRegistry by adding new JavaType entries as discussed in Compositional basic mapping and TypeContributor.

Mapping an AttributeConverter using HBM mappings

When using HBM mappings, you can still make use of the Jakarta Persistence AttributeConverter because Hibernate supports such mapping via the type attribute as demonstrated by the following example.

Let’s consider we have an application-specific Money type:

Example 73. Application-specific Money type
public class Money {

    private long cents;

    public Money(long cents) {
        this.cents = cents;
    }

    public long getCents() {
        return cents;
    }

    public void setCents(long cents) {
        this.cents = cents;
    }
}

Now, we want to use the Money type when mapping the Account entity:

Example 74. Account entity using the Money type
public class Account {

    private Long id;

    private String owner;

    private Money balance;

    //Getters and setters are omitted for brevity
}

Since Hibernate has no knowledge how to persist the Money type, we could use a Jakarta Persistence AttributeConverter to transform the Money type as a Long. For this purpose, we are going to use the following MoneyConverter utility:

Example 75. MoneyConverter implementing the Jakarta Persistence AttributeConverter interface
public class MoneyConverter
        implements AttributeConverter<Money, Long> {

    @Override
    public Long convertToDatabaseColumn(Money attribute) {
        return attribute == null ? null : attribute.getCents();
    }

    @Override
    public Money convertToEntityAttribute(Long dbData) {
        return dbData == null ? null : new Money(dbData);
    }
}

To map the MoneyConverter using HBM configuration files you need to use the converted:: prefix in the type attribute of the property element.

Example 76. HBM mapping for AttributeConverter
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="org.hibernate.orm.test.mapping.converter.hbm">
    <class name="org.hibernate.orm.test.mapping.converter.hbm.Account" table="account" >
        <id name="id"/>

        <property name="owner"/>

        <property name="balance"
            type="converted::org.hibernate.orm.test.mapping.converter.hbm.MoneyConverter"/>

    </class>
</hibernate-mapping>
AttributeConverter Mutability Plan

A basic type that’s converted by a Jakarta Persistence AttributeConverter is immutable if the underlying Java type is immutable and is mutable if the associated attribute type is mutable as well.

Therefore, mutability is given by the JavaType#getMutabilityPlan of the associated entity attribute type.

This can be adjusted by using @Immutable or @Mutability on any of:

  1. the basic value

  2. the AttributeConverter class

  3. the basic value type

See Mapping basic values for additional details.

Immutable types

If the entity attribute is a String, a primitive wrapper (e.g. Integer, Long), an Enum type, or any other immutable Object type, then you can only change the entity attribute value by reassigning it to a new value.

Considering we have the same Period entity attribute as illustrated in the AttributeConverters section:

@Entity(name = "Event")
public static class Event {

    @Id
    @GeneratedValue
    private Long id;

    @Convert(converter = PeriodStringConverter.class)
    @Column(columnDefinition = "")
    private Period span;

    //Getters and setters are omitted for brevity

}

The only way to change the span attribute is to reassign it to a different value:

 Event event = entityManager.createQuery("from Event", Event.class).getSingleResult();
 event.setSpan(Period
     .ofYears(3)
     .plusMonths(2)
     .plusDays(1)
);
Mutable types

On the other hand, consider the following example where the Money type is a mutable.

public static class Money {

	private long cents;

	//Getters and setters are omitted for brevity
}

@Entity(name = "Account")
public static class Account {

	@Id
	private Long id;

	private String owner;

	@Convert(converter = MoneyConverter.class)
	private Money balance;

	//Getters and setters are omitted for brevity
}

public static class MoneyConverter
		implements AttributeConverter<Money, Long> {

	@Override
	public Long convertToDatabaseColumn(Money attribute) {
		return attribute == null ? null : attribute.getCents();
	}

	@Override
	public Money convertToEntityAttribute(Long dbData) {
		return dbData == null ? null : new Money(dbData);
	}
}

A mutable Object allows you to modify its internal structure, and Hibernate’s dirty checking mechanism is going to propagate the change to the database:

Account account = entityManager.find(Account.class, 1L);
account.getBalance().setCents(150 * 100L);
entityManager.persist(account);

Although the AttributeConverter types can be mutable so that dirty checking, deep copying, and second-level caching work properly, treating these as immutable (when they really are) is more efficient.

For this reason, prefer immutable types over mutable ones whenever possible.

Using the AttributeConverter entity property as a query parameter

Assuming you have the following entity:

Example 77. Photo entity with AttributeConverter
@Entity(name = "Photo")
public static class Photo {

	@Id
	private Integer id;

	@Column(length = 256)
	private String name;

	@Column(length = 256)
	@Convert(converter = CaptionConverter.class)
	private Caption caption;

	//Getters and setters are omitted for brevity
}

And the Caption class looks as follows:

Example 78. Caption Java object
public static class Caption {

	private String text;

	public Caption(String text) {
		this.text = text;
	}

	public String getText() {
		return text;
	}

	public void setText(String text) {
		this.text = text;
	}

	@Override
	public boolean equals(Object o) {
		if ( this == o ) {
			return true;
		}
		if ( o == null || getClass() != o.getClass() ) {
			return false;
		}
		Caption caption = (Caption) o;
		return text != null ? text.equals( caption.text ) : caption.text == null;

	}

	@Override
	public int hashCode() {
		return text != null ? text.hashCode() : 0;
	}
}

And we have an AttributeConverter to handle the Caption Java object:

Example 79. Caption Java object AttributeConverter
public static class CaptionConverter
		implements AttributeConverter<Caption, String> {

	@Override
	public String convertToDatabaseColumn(Caption attribute) {
		return attribute.getText();
	}

	@Override
	public Caption convertToEntityAttribute(String dbData) {
		return new Caption( dbData );
	}
}

Traditionally, you could only use the DB data Caption representation, which in our case is a String, when referencing the caption entity property.

Example 80. Filtering by the Caption property using the DB data representation
Photo photo = entityManager.createQuery(
				"select p " +
						"from Photo p " +
						"where upper(caption) = upper(:caption) ", Photo.class )
		.setParameter( "caption", "Nicolae Grigorescu" )
		.getSingleResult();

In order to use the Java object Caption representation, you have to get the associated Hibernate Type.

Example 81. Filtering by the Caption property using the Java Object representation
SessionFactoryImplementor sessionFactory = entityManager.getEntityManagerFactory()
		.unwrap( SessionFactoryImplementor.class );
final MappingMetamodelImplementor mappingMetamodel = sessionFactory
		.getRuntimeMetamodels()
		.getMappingMetamodel();

Type captionType = mappingMetamodel
		.getEntityDescriptor( Photo.class )
		.getPropertyType( "caption" );

Photo photo = (Photo) entityManager.createQuery(
				"select p " +
						"from Photo p " +
						"where upper(caption) = upper(:caption) ", Photo.class )
		.unwrap( Query.class )
		.setParameter(
				"caption",
				new Caption( "Nicolae Grigorescu" ),
				(BindableType) captionType
		)
		.getSingleResult();

By passing the associated Hibernate Type, you can use the Caption object when binding the query parameter value.

3.2.51. Registries

We’ve covered JavaTypeRegistry and JdbcTypeRegistry a few times now, mainly in regards to mapping resolution as discussed in Resolving the composition. But they each also serve additional important roles.

The JavaTypeRegistry is a registry of JavaType references keyed by Java type. In addition to mapping resolution, this registry is used to handle Class references exposed in various APIs such as Query parameter types. JavaType references can be registered through @JavaTypeRegistration.

The JdbcTypeRegistry is a registry of JdbcType references keyed by an integer code. As discussed in JdbcType, these type-codes typically match with the corresponding code from java.sql.Types, but that is not a requirement - integers other than those defined by java.sql.Types can be used. This might be useful for mapping JDBC User Data Types (UDTs) or other specialized database-specific types (PostgreSQL’s UUID type, e.g.). In addition to its use in mapping resolution, this registry is also used as the primary source for resolving "discovered" values in a JDBC ResultSet. JdbcType references can be registered through @JdbcTypeRegistration.

See TypeContributor for an alternative to @JavaTypeRegistration and @JdbcTypeRegistration for registration.

3.2.52. TypeContributor

org.hibernate.boot.model.TypeContributor is a contract for overriding or extending parts of the Hibernate type system.

There are many ways to integrate a TypeContributor. The most common is to define the TypeContributor as a Java service (see java.util.ServiceLoader).

TypeContributor is passed a TypeContributions reference, which allows registration of custom JavaType, JdbcType and BasicType references.

While TypeContributor still exposes the ability to register BasicType references, this is considered deprecated. As of 6.0, these BasicType registrations are only used while interpreting hbm.xml mappings, which are themselves considered deprecated. Use Custom type mapping or Compositional basic mapping instead.

3.2.53. Case Study : BitSet

We’ve covered many ways to specify basic value mappings so far. This section will look at mapping the java.util.BitSet type by applying the different techniques covered so far.

Example 82. Implicit BitSet mapping
@Entity(name = "Product")
public static class Product {
	@Id
	private Integer id;

	private BitSet bitSet;

	//Getters and setters are omitted for brevity
}

As mentioned previously, the worst-case fallback for Hibernate mapping a basic type which implements Serializable is to simply serialize it to the database. BitSet does implement Serializable, so by default Hibernate would handle this mapping by serialization.

That is not an ideal mapping. In the following sections we will look at approaches to change various aspects of how the BitSet gets mapped to the database.

Using AttributeConverter

We’ve seen uses of AttributeConverter previously.

This works well in most cases and is portable across Jakarta Persistence providers.

Example 83. BitSet AttributeConverter
@Entity(name = "Product")
public static class Product {
	@Id
	private Integer id;

	@Convert(converter = BitSetConverter.class)
	private BitSet bitSet;

	//Getters and setters are omitted for brevity
}

@Converter(autoApply = true)
public static class BitSetConverter implements AttributeConverter<BitSet,String> {
	@Override
	public String convertToDatabaseColumn(BitSet attribute) {
		return BitSetHelper.bitSetToString(attribute);
	}

	@Override
	public BitSet convertToEntityAttribute(String dbData) {
		return BitSetHelper.stringToBitSet(dbData);
	}
}

The @Convert annotation was used for illustration. Generally such a converter would be auto-applied instead

See AttributeConverters for details.

This greatly improves the reading and writing performance of dealing with these BitSet values because the AttributeConverter does that more efficiently using a simple externalizable form of the BitSet rather than serializing and deserializing the values.

Using a custom JavaTypeDescriptor

As covered in [basic-mapping-explicit], we will define a JavaType for BitSet that maps values to VARCHAR for storage by default.

Example 84. BitSet JavaTypeDescriptor
public class BitSetJavaType extends AbstractClassJavaType<BitSet> {
    public static final BitSetJavaType INSTANCE = new BitSetJavaType();

    public BitSetJavaType() {
        super(BitSet.class);
    }

    @Override
    public MutabilityPlan<BitSet> getMutabilityPlan() {
        return BitSetMutabilityPlan.INSTANCE;
    }

    @Override
    public JdbcType getRecommendedJdbcType(JdbcTypeIndicators indicators) {
        return indicators.getTypeConfiguration()
                .getJdbcTypeRegistry()
                .getDescriptor(Types.VARCHAR);
    }

    @Override
    public String toString(BitSet value) {
        return BitSetHelper.bitSetToString(value);
    }

    @Override
    public BitSet fromString(CharSequence string) {
        return BitSetHelper.stringToBitSet(string.toString());
    }

    @SuppressWarnings("unchecked")
    public <X> X unwrap(BitSet value, Class<X> type, WrapperOptions options) {
        if (value == null) {
            return null;
        }
        if (BitSet.class.isAssignableFrom(type)) {
            return (X) value;
        }
        if (String.class.isAssignableFrom(type)) {
            return (X) toString(value);
        }
        if (type.isArray()) {
            if (type.getComponentType() == byte.class) {
                return (X) value.toByteArray();
            }
        }
        throw unknownUnwrap(type);
    }

    public <X> BitSet wrap(X value, WrapperOptions options) {
        if (value == null) {
            return null;
        }
        if (value instanceof CharSequence) {
            return fromString((CharSequence) value);
        }
        if (value instanceof BitSet) {
            return (BitSet) value;
        }
        throw unknownWrap(value.getClass());
    }

}

We can either apply that type locally using @JavaType

Example 85. @JavaType
@Entity(name = "Product")
public static class Product {
	@Id
	private Integer id;

	@JavaType(BitSetJavaType.class)
	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}

Or we can apply it globally using @JavaTypeRegistration. This allows the registered JavaType to be used as the default whenever we encounter the BitSet type

Example 86. @JavaTypeRegistration
@Entity(name = "Product")
@JavaTypeRegistration(javaType = BitSet.class, descriptorClass = BitSetJavaType.class)
public static class Product {
	@Id
	private Integer id;

	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}
Selecting different JdbcTypeDescriptor

Our custom BitSetJavaType maps BitSet values to VARCHAR by default. That was a better option than direct serialization. But as BitSet is ultimately binary data we would probably really want to map this to VARBINARY type instead. One way to do that would be to change BitSetJavaType#getRecommendedJdbcType to instead return VARBINARY descriptor. Another option would be to use a local @JdbcType or @JdbcTypeCode.

The following examples for specifying the JdbcType assume our BitSetJavaType is globally registered.

We will again store the values as VARBINARY in the database. The difference now however is that the coercion methods #wrap and #unwrap will be used to prepare the value rather than relying on serialization.

Example 87. @JdbcTypeCode
@Entity(name = "Product")
public static class Product {
	@Id
	private Integer id;

	@JdbcTypeCode(Types.VARBINARY)
	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}

In this example, @JdbcTypeCode has been used to indicate that the JdbcType registered for JDBC’s VARBINARY type should be used.

Example 88. @JdbcType
@Entity(name = "Product")
public static class Product {
	@Id
	private Integer id;

	@JdbcType(CustomBinaryJdbcType.class)
	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}

In this example, @JdbcType has been used to specify our custom BitSetJdbcType descriptor locally for this attribute.

We could instead replace how Hibernate deals with all VARBINARY handling with our custom impl using @JdbcTypeRegistration

Example 89. @JdbcType
@Entity(name = "Product")
@JdbcTypeRegistration(CustomBinaryJdbcType.class)
public static class Product {
	@Id
	private Integer id;

	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}

3.2.54. SQL quoted identifiers

You can force Hibernate to quote an identifier in the generated SQL by enclosing the table or column name in backticks in the mapping document. While traditionally, Hibernate used backticks for escaping SQL reserved keywords, Jakarta Persistence uses double quotes instead.

Once the reserved keywords are escaped, Hibernate will use the correct quotation style for the SQL Dialect. This is usually double quotes, but SQL Server uses brackets and MySQL uses backticks.

Example 90. Hibernate quoting
@Entity(name = "Product")
public static class Product {

	@Id
	private Long id;

	@Column(name = "`name`")
	private String name;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}
Example 91. Jakarta Persistence quoting
@Entity(name = "Product")
public static class Product {

	@Id
	private Long id;

	@Column(name = "\"name\"")
	private String name;

	@Column(name = "\"number\"")
	private String number;

	//Getters and setters are omitted for brevity

}

Because name and number are reserved words, the Product entity mapping uses backticks to quote these column names.

When saving the following Product entity, Hibernate generates the following SQL insert statement:

Example 92. Persisting a quoted column name
Product product = new Product();
product.setId(1L);
product.setName("Mobile phone");
product.setNumber("123-456-7890");
entityManager.persist(product);
INSERT INTO Product ("name", "number", id)
VALUES ('Mobile phone', '123-456-7890', 1)
Global quoting

Hibernate can also quote all identifiers (e.g. table, columns) using the following configuration property:

<property
    name="hibernate.globally_quoted_identifiers"
    value="true"
/>

This way, we don’t need to manually quote any identifier:

Example 93. Jakarta Persistence quoting
@Entity(name = "Product")
public static class Product {

	@Id
	private Long id;

	private String name;

	private String number;

	//Getters and setters are omitted for brevity

}

When persisting a Product entity, Hibernate is going to quote all identifiers as in the following example:

INSERT INTO "Product" ("name", "number", "id")
VALUES ('Mobile phone', '123-456-7890', 1)

As you can see, both the table name and all the column have been quoted.

For more about quoting-related configuration properties, check out the Mapping configurations section as well.

3.2.55. Generated properties

NOTE

This section talks about generating values for non-identifier attributes. For discussion of generated identifier values, see Generated identifier values.

Generated attributes have their values generated as part of performing a SQL INSERT or UPDATE. Applications can generate these values in any number of ways (SQL DEFAULT value, trigger, etc). Typically, the application needs to refresh objects that contain any properties for which the database was generating values, which is a major drawback.

Applications can also delegate generation to Hibernate, in which case Hibernate will manage the value generation and (potential[3]) state refresh itself.

Only @Basic and @Version attributes can be marked as generated.

Generated attributes must additionally be non-insertable and non-updateable.

Hibernate supports both in-VM and in-DB generation. A generation that uses the current JVM timestamp as the generated value is an example of an in-VM strategy. A generation that uses the database’s current_timestamp function is an example of an in-DB strategy.

Hibernate supports the following timing (when) for generation:

NEVER (the default)

the given attribute value is not generated

INSERT

the attribute value is generated on insert but is not regenerated on subsequent updates

ALWAYS

the attribute value is generated both on insert and update.

Hibernate supports multiple ways to mark an attribute as generated:

@CurrentTimestamp

The @CurrentTimestamp annotation is an in-DB strategy that can be configured for either INSERT or ALWAYS timing. It uses the database’s current_timestamp function as the generated value

Example 94. @UpdateTimestamp mapping example
@CurrentTimestamp(event = INSERT)
public Instant createdAt;

@CurrentTimestamp(event = {INSERT, UPDATE})
public Instant lastUpdatedAt;
@CreationTimestamp

The @CreationTimestamp annotation is an in-VM INSERT strategy. Hibernate will use the current timestamp of the JVM as the insert value for the attribute.

Supports most temporal types (java.time.Instant, java.util.Date, java.util.Calendar, etc)

Example 95. @CreationTimestamp mapping example
@Entity(name = "Event")
public static class Event {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`timestamp`")
	@CreationTimestamp
	private Date timestamp;

	//Constructors, getters, and setters are omitted for brevity
}

While inserting the Event, Hibernate will populate the underlying timestamp column with the current JVM timestamp value

@UpdateTimestamp annotation

The @UpdateTimestamp annotation is an in-VM INSERT strategy. Hibernate will use the current timestamp of the JVM as the insert and update value for the attribute.

Supports most temporal types (java.time.Instant, java.util.Date, java.util.Calendar, etc)

Example 96. @UpdateTimestamp mapping example
@Entity(name = "Bid")
public static class Bid {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "updated_on")
	@UpdateTimestamp
	private Date updatedOn;

	@Column(name = "updated_by")
	private String updatedBy;

	private Long cents;

	//Getters and setters are omitted for brevity

}
@Generated annotation

The @Generated annotation is an in-DB strategy that can be configured for either INSERT or ALWAYS timing

This is the legacy mapping for in-DB generated values.

Example 97. @Generated mapping example
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	private String middleName1;

	private String middleName2;

	private String middleName3;

	private String middleName4;

	private String middleName5;

	@Generated(event = {INSERT,UPDATE})
	@Column(columnDefinition =
		"AS CONCAT(" +
		"	COALESCE(firstName, ''), " +
		"	COALESCE(' ' + middleName1, ''), " +
		"	COALESCE(' ' + middleName2, ''), " +
		"	COALESCE(' ' + middleName3, ''), " +
		"	COALESCE(' ' + middleName4, ''), " +
		"	COALESCE(' ' + middleName5, ''), " +
		"	COALESCE(' ' + lastName, '') " +
		")")
	private String fullName;

}
Custom generation strategy

Hibernate also supports value generation via a pluggable API using @ValueGenerationType and AnnotationValueGeneration allowing users to define any generation strategy they wish.

Let’s look at an example of generating UUID values. First the attribute mapping

Example 98. Custom generation mapping example
@GeneratedUuidValue( timing = GenerationTiming.INSERT )
public UUID createdUuid;

@GeneratedUuidValue( timing = GenerationTiming.ALWAYS )
   public UUID updatedUuid;

This example makes use of an annotation named @GeneratedUuidValue - but where is that annotation defined? This is a custom annotations provided by the application.

Example 99. Custom generation mapping example
@ValueGenerationType( generatedBy = UuidValueGeneration.class )
@Retention(RetentionPolicy.RUNTIME)
@Target( { ElementType.FIELD, ElementType.METHOD, ElementType.ANNOTATION_TYPE } )
@Inherited
public @interface GeneratedUuidValue {
	GenerationTiming timing();
}

The @ValueGenerationType( generatedBy = UuidValueGeneration.class ) here is the important piece; it tells Hibernate how to generate values for the attribute - here it will use the specified UuidValueGeneration class

Example 100. Custom generation mapping example
public static class UuidValueGeneration implements BeforeExecutionGenerator {
	private final EnumSet<EventType> eventTypes;

	public UuidValueGeneration(GeneratedUuidValue annotation) {
		eventTypes = annotation.timing().getEquivalent().eventTypes();
	}

	@Override
	public EnumSet<EventType> getEventTypes() {
		return eventTypes;
	}

	@Override
	public Object generate(SharedSessionContractImplementor session, Object owner, Object currentValue, EventType eventType) {
		return SafeRandomUUIDGenerator.safeRandomUUID();
	}
}

See @ValueGenerationType and AnnotationValueGeneration for details of each contract

3.2.56. Column transformers: read and write expressions

Hibernate allows you to customize the SQL it uses to read and write the values of columns mapped to @Basic types. For example, if your database provides a set of data encryption functions, you can invoke them for individual columns like in the following example.

Example 101. @ColumnTransformer example
	@Entity(name = "Employee")
	public static class Employee {

		@Id
		private Long id;

		@NaturalId
		private String username;

		@Column(name = "pswd")
		@ColumnTransformer(
			read = "decrypt('AES', '00', pswd )",
			write = "encrypt('AES', '00', ?)"
		)
// For H2 2.0.202+ one must use the varbinary DDL type
//		@Column(name = "pswd", columnDefinition = "varbinary")
//		@ColumnTransformer(
//			read = "trim(trailing u&'\\0000' from cast(decrypt('AES', '00', pswd ) as character varying))",
//			write = "encrypt('AES', '00', ?)"
//		)
		private String password;

		private int accessLevel;

		@ManyToOne(fetch = FetchType.LAZY)
		private Department department;

		@ManyToMany(mappedBy = "employees")
		private List<Project> projects = new ArrayList<>();

		//Getters and setters omitted for brevity
	}

If a property uses more than one column, you must use the forColumn attribute to specify which column the @ColumnTransformer read and write expressions are targeting.

Example 102. @ColumnTransformer forColumn attribute usage
@Entity(name = "Savings")
public static class Savings {

	@Id
	private Long id;

	@CompositeType(MonetaryAmountUserType.class)
	@AttributeOverrides({
		@AttributeOverride(name = "amount", column = @Column(name = "money")),
		@AttributeOverride(name = "currency", column = @Column(name = "currency"))
	})
	@ColumnTransformer(
			forColumn = "money",
			read = "money / 100",
			write = "? * 100"
	)
	private MonetaryAmount wallet;

	//Getters and setters omitted for brevity

}

Hibernate applies the custom expressions automatically whenever the property is referenced in a query. This functionality is similar to a derived-property @Formula with two differences:

  • The property is backed by one or more columns that are exported as part of automatic schema generation.

  • The property is read-write, not read-only.

The write expression, if specified, must contain exactly one '?' placeholder for the value.

Example 103. Persisting an entity with a @ColumnTransformer and a composite type
doInJPA(this::entityManagerFactory, entityManager -> {
	Savings savings = new Savings();
	savings.setId(1L);
	savings.setWallet(new MonetaryAmount(BigDecimal.TEN, Currency.getInstance(Locale.US)));
	entityManager.persist(savings);
});

doInJPA(this::entityManagerFactory, entityManager -> {
	Savings savings = entityManager.find(Savings.class, 1L);
	assertEquals(10, savings.getWallet().getAmount().intValue());
	assertEquals(Currency.getInstance(Locale.US), savings.getWallet().getCurrency());
});
INSERT INTO Savings (money, currency, id)
VALUES (10 * 100, 'USD', 1)

SELECT
    s.id as id1_0_0_,
    s.money / 100 as money2_0_0_,
    s.currency as currency3_0_0_
FROM
    Savings s
WHERE
    s.id = 1

3.3. Embeddable values

Historically Hibernate called these components. Jakarta Persistence calls them embeddables. Either way, the concept is the same: a composition of values.

For example, we might have a Publisher class that is a composition of name and country, or a Location class that is a composition of country and city.

Usage of the word embeddable

To avoid any confusion with the annotation that marks a given embeddable type, the annotation will be further referred to as @Embeddable.

Throughout this chapter and thereafter, for brevity sake, embeddable types may also be referred to as embeddable.

Example 104. Embeddable type example
@Embeddable
public static class Publisher {

	private String name;

	private Location location;

	public Publisher(String name, Location location) {
		this.name = name;
		this.location = location;
	}

	private Publisher() {}

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class Location {

	private String country;

	private String city;

	public Location(String country, String city) {
		this.country = country;
		this.city = city;
	}

	private Location() {}

	//Getters and setters are omitted for brevity
}

An embeddable type is another form of a value type, and its lifecycle is bound to a parent entity type, therefore inheriting the attribute access from its parent (for details on attribute access, see Access strategies).

Embeddable types can be made up of basic values as well as associations, with the caveat that, when used as collection elements, they cannot define collections themselves.

3.3.1. Component / Embedded

Most often, embeddable types are used to group multiple basic type mappings and reuse them across several entities.

Example 105. Simple Embeddable
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	private Publisher publisher;

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class Publisher {

	@Column(name = "publisher_name")
	private String name;

	@Column(name = "publisher_country")
	private String country;

	//Getters and setters, equals and hashCode methods omitted for brevity

}
create table Book (
    id bigint not null,
    author varchar(255),
    publisher_country varchar(255),
    publisher_name varchar(255),
    title varchar(255),
    primary key (id)
)

Jakarta Persistence defines two terms for working with an embeddable type: @Embeddable and @Embedded.

@Embeddable is used to describe the mapping type itself (e.g. Publisher).

@Embedded is for referencing a given embeddable type (e.g. book.publisher).

So, the embeddable type is represented by the Publisher class and the parent entity makes use of it through the book#publisher object composition.

The composed values are mapped to the same table as the parent table. Composition is part of good object-oriented data modeling (idiomatic Java). In fact, that table could also be mapped by the following entity type instead.

Example 106. Alternative to embeddable type composition
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	@Column(name = "publisher_name")
	private String publisherName;

	@Column(name = "publisher_country")
	private String publisherCountry;

	//Getters and setters are omitted for brevity
}

The composition form is certainly more object-oriented, and that becomes more evident as we work with multiple embeddable types.

3.3.2. Overriding Embeddable types

Although from an object-oriented perspective, it’s much more convenient to work with embeddable types, when we reuse the same embeddable multiple times on the same class, the Jakarta Persistence specification requires to set the associated column names explicitly.

This requirement is due to how object properties are mapped to database columns. By default, Jakarta Persistence expects a database column having the same name with its associated object property. When including multiple embeddables, the implicit name-based mapping rule doesn’t work anymore because multiple object properties could end-up being mapped to the same database column.

When an embeddable type is used multiple times, Jakarta Persistence defines the @AttributeOverride and @AssociationOverride annotations to handle this scenario to override the default column names defined by the Embeddable.

See Embeddables and ImplicitNamingStrategy for an alternative to using @AttributeOverride and @AssociationOverride

Considering you have the following Publisher embeddable type which defines a @ManyToOne association with the Country entity:

Example 107. Embeddable type with a @ManyToOne association
@Embeddable
public static class Publisher {

	private String name;

	@ManyToOne(fetch = FetchType.LAZY)
	private Country country;

	//Getters and setters, equals and hashCode methods omitted for brevity

}

@Entity(name = "Country")
public static class Country {

	@Id
	@GeneratedValue
	private Long id;

	@NaturalId
	private String name;

	//Getters and setters are omitted for brevity
}
create table Country (
    id bigint not null,
    name varchar(255),
    primary key (id)
)

alter table Country
    add constraint UK_p1n05aafu73sbm3ggsxqeditd
    unique (name)

Now, if you have a Book entity which declares two Publisher embeddable types for the ebook and paperback versions, you cannot use the default Publisher embeddable mapping since there will be a conflict between the two embeddable column mappings.

Therefore, the Book entity needs to override the embeddable type mappings for each Publisher attribute:

Example 108. Overriding embeddable type attributes
@Entity(name = "Book")
@AttributeOverrides({
		@AttributeOverride(
				name = "ebookPublisher.name",
				column = @Column(name = "ebook_pub_name")
		),
		@AttributeOverride(
				name = "paperBackPublisher.name",
				column = @Column(name = "paper_back_pub_name")
		)
})
@AssociationOverrides({
		@AssociationOverride(
				name = "ebookPublisher.country",
				joinColumns = @JoinColumn(name = "ebook_pub_country_id")
		),
		@AssociationOverride(
				name = "paperBackPublisher.country",
				joinColumns = @JoinColumn(name = "paper_back_pub_country_id")
		)
})
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	private Publisher ebookPublisher;

	private Publisher paperBackPublisher;

	//Getters and setters are omitted for brevity
}
create table Book (
    id bigint not null,
    author varchar(255),
    ebook_pub_name varchar(255),
    paper_back_pub_name varchar(255),
    title varchar(255),
    ebook_pub_country_id bigint,
    paper_back_pub_country_id bigint,
    primary key (id)
)

alter table Book
    add constraint FKm39ibh5jstybnslaoojkbac2g
    foreign key (ebook_pub_country_id)
    references Country

alter table Book
    add constraint FK7kqy9da323p7jw7wvqgs6aek7
    foreign key (paper_back_pub_country_id)
    references Country

3.3.3. Collections of embeddable types

Collections of embeddable types are specifically valued collections (as embeddable types are value types). Value collections are covered in detail in Collections of value types.

3.3.4. Embeddable type as a Map key

Embeddable types can also be used as Map keys. This topic is converted in detail in Map - key.

3.3.5. Embeddable type as identifier

Embeddable types can also be used as entity type identifiers. This usage is covered in detail in Composite identifiers.

Embeddable types that are used as collection entries, map keys or entity type identifiers cannot include their own collection mappings.

3.3.6. @Target mapping

The @Target annotation is used to specify the implementation class of a given association that is mapped via an interface. The @ManyToOne, @OneToOne, @OneToMany, and @ManyToMany feature a targetEntity attribute to specify the actual class of the entity association when an interface is used for the mapping.

The @ElementCollection association has a targetClass attribute for the same purpose.

However, for simple embeddable types, there is no such construct and so you need to use the Hibernate-specific @Target annotation instead.

Example 109. @Target mapping usage
public interface Coordinates {
	double x();
	double y();
}

@Embeddable
public static class GPS implements Coordinates {

	private double latitude;

	private double longitude;

	private GPS() {
	}

	public GPS(double latitude, double longitude) {
		this.latitude = latitude;
		this.longitude = longitude;
	}

	@Override
	public double x() {
		return latitude;
	}

	@Override
	public double y() {
		return longitude;
	}
}

@Entity(name = "City")
public static class City {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	@Embedded
	@Target(GPS.class)
	private Coordinates coordinates;

	//Getters and setters omitted for brevity

}

The coordinates embeddable type is mapped as the Coordinates interface. However, Hibernate needs to know the actual implementation type, which is GPS in this case, hence the @Target annotation is used to provide this information.

Assuming we have persisted the following City entity:

Example 110. @Target persist example
doInJPA(this::entityManagerFactory, entityManager -> {

	City cluj = new City();
	cluj.setName("Cluj");
	cluj.setCoordinates(new GPS(46.77120, 23.62360));

	entityManager.persist(cluj);
});

When fetching the City entity, the coordinates property is mapped by the @Target expression:

Example 111. @Target fetching example
doInJPA(this::entityManagerFactory, entityManager -> {

	City cluj = entityManager.find(City.class, 1L);

	assertEquals(46.77120, cluj.getCoordinates().x(), 0.00001);
	assertEquals(23.62360, cluj.getCoordinates().y(), 0.00001);
});
SELECT
    c.id as id1_0_0_,
    c.latitude as latitude2_0_0_,
    c.longitude as longitud3_0_0_,
    c.name as name4_0_0_
FROM
    City c
WHERE
    c.id = ?

-- binding parameter [1] as [BIGINT] - [1]

-- extracted value ([latitude2_0_0_] : [DOUBLE])  - [46.7712]
-- extracted value ([longitud3_0_0_] : [DOUBLE])  - [23.6236]
-- extracted value ([name4_0_0_]     : [VARCHAR]) - [Cluj]

Therefore, the @Target annotation is used to define a custom join association between the parent-child association.

3.3.7. @Parent mapping

The Hibernate-specific @Parent annotation allows you to reference the owner entity from within an embeddable.

Example 112. @Parent mapping usage
@Embeddable
public static class GPS {

	private double latitude;

	private double longitude;

	@Parent
	private City city;

	//Getters and setters omitted for brevity

}

@Entity(name = "City")
public static class City {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	@Embedded
	@Target(GPS.class)
	private GPS coordinates;

	//Getters and setters omitted for brevity

}

Assuming we have persisted the following City entity:

Example 113. @Parent persist example
doInJPA(this::entityManagerFactory, entityManager -> {

	City cluj = new City();
	cluj.setName("Cluj");
	cluj.setCoordinates(new GPS(46.77120, 23.62360));

	entityManager.persist(cluj);
});

When fetching the City entity, the city property of the embeddable type acts as a back reference to the owning parent entity:

Example 114. @Parent fetching example
doInJPA(this::entityManagerFactory, entityManager -> {

	City cluj = entityManager.find(City.class, 1L);

	assertSame(cluj, cluj.getCoordinates().getCity());
});

Therefore, the @Parent annotation is used to define the association between an embeddable type and the owning entity.

3.3.8. Custom instantiation

Jakarta Persistence requires embeddable classes to follow Java Bean conventions. Part of this is the definition of a non-arg constructor. However, not all value compositions applications might map as embeddable values follow Java Bean conventions - e.g. a struct or Java 15 record.

Hibernate allows the use of a custom instantiator for creating the embeddable instances through the org.hibernate.metamodel.spi.EmbeddableInstantiator contract. For example, consider the following embeddable:

Example 115. EmbeddableInstantiator - Embeddable
@Embeddable
public class Name {
	@Column(name = "first_name")
	private final String first;
	@Column(name = "last_name")
	private final String last;

	private Name() {
		throw new UnsupportedOperationException();
	}

	public Name(String first, String last) {
		this.first = first;
		this.last = last;
	}

	public String getFirstName() {
		return first;
	}

	public String getLastName() {
		return last;
	}
}

Here, Name only allows use of the constructor accepting its state. Because this class does not follow Java Bean conventions, in terms of constructor, a custom strategy for instantiation is needed.

Example 116. EmbeddableInstantiator - Implementation
public class NameInstantiator implements EmbeddableInstantiator {
	@Override
	public Object instantiate(ValueAccess valueAccess, SessionFactoryImplementor sessionFactory) {
		// alphabetical
		final String first = valueAccess.getValue( 0, String.class );
		final String last = valueAccess.getValue( 1, String.class );
		return new Name( first, last );
	}

	// ...

}

There are a few ways to specify the custom instantiator. The @org.hibernate.annotations.EmbeddableInstantiator annotation can be used on the embedded attribute:

Example 117. @EmbeddableInstantiator on attribute
@Entity
public class Person {
	@Id
	public Integer id;
	@Embedded
	@EmbeddableInstantiator( NameInstantiator.class )
	public Name name;
	@ElementCollection
	@Embedded
	@EmbeddableInstantiator( NameInstantiator.class )
	public Set<Name> aliases;

}

@EmbeddableInstantiator may also be specified on the embeddable class:

Example 118. @EmbeddableInstantiator on class
@Embeddable
@EmbeddableInstantiator( NameInstantiator.class )
public class Name {
	@Column(name = "first_name")
	private final String first;
	@Column(name = "last_name")
	private final String last;

	private Name() {
		throw new UnsupportedOperationException();
	}

	public Name(String first, String last) {
		this.first = first;
		this.last = last;
	}

	public String getFirstName() {
		return first;
	}

	public String getLastName() {
		return last;
	}
}

@Entity
public class Person {
	@Id
	public Integer id;
	@Embedded
	public Name name;
	@ElementCollection
	@Embedded
	public Set<Name> aliases;
}

Lastly, @org.hibernate.annotations.EmbeddableInstantiatorRegistration may be used, which is useful when the application developer does not control the embeddable to be able to apply the instantiator on the embeddable.

Example 119. @EmbeddableInstantiatorRegistration
@Entity
@EmbeddableInstantiatorRegistration( embeddableClass = Name.class, instantiator = NameInstantiator.class )
public class Person {
	@Id
	public Integer id;
	@Embedded
	public Name name;
	@ElementCollection
	@Embedded
	public Set<Name> aliases;

}

3.3.9. Custom type mapping

Another approach is to supply the implementation of the org.hibernate.usertype.CompositeUserType contract using @CompositeType, which is an extension to the org.hibernate.metamodel.spi.EmbeddableInstantiator contract.

There are also corresponding, specialized forms of @CompositeType for specific model parts:

  • When mapping a Map, @CompositeType describes the Map value while @MapKeyCompositeType describes the Map key

  • For collection mappings, @CompositeType describes the elements

For example, consider the following custom type:

Example 120. CompositeUserType - Domain type
public class Name {
	private final String first;
	private final String last;

	public Name(String first, String last) {
		this.first = first;
		this.last = last;
	}

	public String firstName() {
		return first;
	}

	public String lastName() {
		return last;
	}
}

Here, Name only allows use of the constructor accepting its state. Because this class does not follow Java Bean conventions, a custom user type for instantiation and state access is needed.

Example 121. CompositeUserType - Implementation
public class NameCompositeUserType implements CompositeUserType<Name> {

	public static class NameMapper {
		String firstName;
		String lastName;
	}

	@Override
	public Class<?> embeddable() {
		return NameMapper.class;
	}

	@Override
	public Class<Name> returnedClass() {
		return Name.class;
	}

	@Override
	public Name instantiate(ValueAccess valueAccess, SessionFactoryImplementor sessionFactory) {
		// alphabetical
		final String first = valueAccess.getValue( 0, String.class );
		final String last = valueAccess.getValue( 1, String.class );
		return new Name( first, last );
	}

	@Override
	public Object getPropertyValue(Name component, int property) throws HibernateException {
		// alphabetical
		switch ( property ) {
			case 0:
				return component.firstName();
			case 1:
				return component.lastName();
		}
		return null;
	}

	@Override
	public boolean equals(Name x, Name y) {
		return x == y || x != null && Objects.equals( x.firstName(), y.firstName() )
				&& Objects.equals( x.lastName(), y.lastName() );
	}

	@Override
	public int hashCode(Name x) {
		return Objects.hash( x.firstName(), x.lastName() );
	}

	@Override
	public Name deepCopy(Name value) {
		return value; // immutable
	}

	@Override
	public boolean isMutable() {
		return false;
	}

	@Override
	public Serializable disassemble(Name value) {
		return new String[] { value.firstName(), value.lastName() };
	}

	@Override
	public Name assemble(Serializable cached, Object owner) {
		final String[] parts = (String[]) cached;
		return new Name( parts[0], parts[1] );
	}

	@Override
	public Name replace(Name detached, Name managed, Object owner) {
		return detached;
	}

}

A composite user type needs an embeddable mapper class, which represents the embeddable mapping structure of the type i.e. the way the type would look like if you had the option to write a custom @Embeddable class.

In addition to the instantiation logic, a composite user type also has to provide a way to decompose the returned type into the individual components/properties of the embeddable mapper class through getPropertyValue. The property index, just like in the instantiate method, is based on the alphabetical order of the attribute names of the embeddable mapper class.

The composite user type also needs to provide methods to handle the mutability, equals, hashCode and the cache serialization and deserialization of the returned type.

There are a few ways to specify the composite user type. The @org.hibernate.annotations.CompositeType annotation can be used on the embedded and element collection attributes:

Example 122. @CompositeType on attribute
@Entity
public class Person {
	@Id
	public Integer id;

	@Embedded
	@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
	@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
	@CompositeType( NameCompositeUserType.class )
	public Name name;

	@ElementCollection
	@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
	@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
	@CompositeType( NameCompositeUserType.class )
	public Set<Name> aliases;

}

Or @org.hibernate.annotations.CompositeTypeRegistration may be used, which is useful when the application developer wants to apply the composite user type for all domain type uses.

Example 123. @CompositeTypeRegistration
@Entity
@CompositeTypeRegistration( embeddableClass = Name.class, userType = NameCompositeUserType.class )
public class Person {
	@Id
	public Integer id;

	@Embedded
	@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
	@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
	public Name name;

	@ElementCollection
	@AttributeOverride(name = "firstName", column = @Column(name = "first_name"))
	@AttributeOverride(name = "lastName", column = @Column(name = "last_name"))
	public Set<Name> aliases;

}

3.3.10. Embeddables and ImplicitNamingStrategy

The ImplicitNamingStrategyComponentPathImpl is a Hibernate-specific feature. Users concerned with Jakarta Persistence provider portability should instead prefer explicit column naming with @AttributeOverride.

Hibernate naming strategies are covered in detail in Naming. However, for the purposes of this discussion, Hibernate has the capability to interpret implicit column names in a way that is safe for use with multiple embeddable types.

Example 124. Implicit multiple embeddable type mapping
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	private Publisher ebookPublisher;

	private Publisher paperBackPublisher;

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class Publisher {

	private String name;

	@ManyToOne(fetch = FetchType.LAZY)
	private Country country;

	//Getters and setters, equals and hashCode methods omitted for brevity
}

@Entity(name = "Country")
public static class Country {

	@Id
	@GeneratedValue
	private Long id;

	@NaturalId
	private String name;

	//Getters and setters are omitted for brevity
}

To make it work, you need to use the ImplicitNamingStrategyComponentPathImpl naming strategy.

Example 125. Enabling implicit embeddable type mapping using the component path naming strategy
metadataBuilder.applyImplicitNamingStrategy(
	ImplicitNamingStrategyComponentPathImpl.INSTANCE
);

Now the "path" to attributes are used in the implicit column naming:

create table Book (
    id bigint not null,
    author varchar(255),
    ebookPublisher_name varchar(255),
    paperBackPublisher_name varchar(255),
    title varchar(255),
    ebookPublisher_country_id bigint,
    paperBackPublisher_country_id bigint,
    primary key (id)
)

You could even develop your own naming strategy to do other types of implicit naming strategies.

3.3.11. Aggregate embeddable mapping

An embeddable mapping is usually just a way to encapsulate columns of a table into a Java type, but as of Hibernate 6.2, it is also possible to map embeddable types as SQL aggregate types.

Currently, there are three possible SQL aggregate types which can be specified by annotating one of the following annotations on a persistent attribute:

  • @Struct - maps to a named SQL object type

  • @JdbcTypeCode(SqlTypes.JSON) - maps to the SQL type JSON

  • @JdbcTypeCode(SqlTypes.SQLXML) - maps to the SQL type XML

Any read or assignment (in an update statement) expression for an attribute of such an embeddable will resolve to the proper SQL expression to access/update the attribute of the SQL type.

Since object, JSON and XML types are not supported equally on all databases, beware that not every mapping will work on all databases. The following table outlines the current support for the different aggregate types:

Database Struct JSON XML

PostgreSQL

Yes

Yes

No (not yet)

Oracle

Yes

Yes

No (not yet)

DB2

Yes

No (not yet)

No (not yet)

SQL Server

No (not yet)

No (not yet)

No (not yet)

Also note that embeddable types that are used in aggregate mappings do not yet support all kinds of attribute mappings, most notably:

  • Association mappings (@ManyToOne, @OneToOne, @OneToMany, @ManyToMany, @ElementCollection)

  • Basic array mappings

@Struct aggregate embeddable mapping

The @Struct annotation can be placed on either the persistent attribute, or the embeddable type, and requires the specification of a name i.e. the name of the SQL object type that it maps to.

The following example mapping, maps the EmbeddableAggregate type to the SQL object type structType:

Example 126. Mapping embeddable as SQL object type on persistent attribute level
@Entity(name = "StructHolder")
public static class StructHolder {

	@Id
	private Long id;
	@Struct(name = "structType")
	private EmbeddableAggregate aggregate;

}

The schema generation will by default emit DDL for that object type, which looks something along the lines of

create type structType as (
    ...
)
create table StructHolder as (
    id bigint not null primary key,
    aggregate structType
)

The name and the nullability of the column can be refined through applying a @Column on the persistent attribute.

One very important thing to note is that the order of columns in the DDL definition of a type must match the order that Hibernate expects. By default, the order of columns is based on the alphabetical ordering of the embeddable type attribute names.

Consider the following class:

@Embeddable
@Struct(name = "myStruct")
public class MyStruct {
	@Column(name = "b")
	String attr1;
	@Column(name = "a")
	String attr2;
}

The expected ordering of columns will be (b,a), because the name attr1 comes before attr2 in alphabetical ordering. This example aims at showing the importance of the persistent attribute name.

Defining the embeddable type as Java record instead of a class can force a particular ordering through the definition of canonical constructor.

@Embeddable
@Struct(name = "myStruct")
public record MyStruct (
	@Column(name = "a")
	String attr2,
	@Column(name = "b")
	String attr1
) {}

In this particular example, the expected ordering of columns will be (a,b), because the canonical constructor of the record defines a specific ordering of persistent attributes, which Hibernate makes use of for @Struct mappings.

It is not necessary to switch to Java records to configure the order though. The @Struct annotation allows specifying the order through the attributes member, an array of attribute names that the embeddable type declares, which defines the order in columns appear in the SQL object type.

The same ordering as with the Java record can be achieved this way:

@Embeddable
@Struct(name = "myStruct", attributes = {"attr2", "attr1"})
public class MyStruct {
	@Column(name = "b")
	String attr1;
	@Column(name = "a")
	String attr2;
}
JSON/XML aggregate embeddable mapping

The @JdbcTypeCode annotation for JSON and XML mappings can only be placed on the persistent attribute.

The following example mapping, maps the EmbeddableAggregate type to the JSON SQL type:

Example 127. Mapping embeddable as JSON
@Entity(name = "JsonHolder")
public static class JsonHolder {

	@Id
	private Long id;
	@JdbcTypeCode(SqlTypes.JSON)
	private EmbeddableAggregate aggregate;

}

The schema generation will by default emit DDL that ensures the constraints of the embeddable type are respected, which looks something along the lines of

create table JsonHolder as (
    id bigint not null primary key,
    aggregate json,
    check (json_value(aggregate, '$.attribute1') is not null)
)

Again, the name and the nullability of the aggregate column can be refined through applying a @Column on the persistent attribute.

3.3.12. Embeddable mappings containing collections

Mapping collections inside an @Embeddable value is supported in most cases. There are a couple exceptions:

  • If the values of an @ElementCollection is of embeddable type, that embeddable cannot contain nested collections;

  • Explicitly selecting an embeddable that contains collections in a query is currently not supported (we wouldn’t be able to correctly initialize the collection since its owning entity instance would be missing from the Persistence Context).

3.4. Entity types

Usage of the word entity

The entity type describes the mapping between the actual persistable domain model object and a database table row. To avoid any confusion with the annotation that marks a given entity type, the annotation will be further referred to as @Entity.

Throughout this chapter and thereafter, entity types will be simply referred to as entity.

3.4.1. POJO Models

Section 2.1 The Entity Class of the Java Persistence 2.1 specification defines its requirements for an entity class. Applications that wish to remain portable across Jakarta Persistence providers should adhere to these requirements:

  • The entity class must be annotated with the jakarta.persistence.Entity annotation (or be denoted as such in XML mapping).

  • The entity class must have a public or protected no-argument constructor. It may define additional constructors as well.

  • The entity class must be a top-level class.

  • An enum or interface may not be designated as an entity.

  • The entity class must not be final. No methods or persistent instance variables of the entity class may be final.

  • If an entity instance is to be used remotely as a detached object, the entity class must implement the Serializable interface.

  • Both abstract and concrete classes can be entities. Entities may extend non-entity classes as well as entity classes, and non-entity classes may extend entity classes.

  • The persistent state of an entity is represented by instance variables, which may correspond to JavaBean-style properties. An instance variable must be directly accessed only from within the methods of the entity by the entity instance itself. The state of the entity is available to clients only through the entity’s accessor methods (getter/setter methods) or other business methods.

Hibernate, however, is not as strict in its requirements. The differences from the list above include:

  • The entity class must have a no-argument constructor, which may be public, protected or package visibility. It may define additional constructors as well.

  • The entity class need not be a top-level class.

  • Technically Hibernate can persist final classes or classes with final persistent state accessor (getter/setter) methods. However, it is generally not a good idea as doing so will stop Hibernate from being able to generate proxies for lazy-loading the entity.

  • Hibernate does not restrict the application developer from exposing instance variables and referencing them from outside the entity class itself. The validity of such a paradigm, however, is debatable at best.

Let’s look at each requirement in detail.

3.4.2. Prefer non-final classes

A central feature of Hibernate is the ability to load lazily certain entity instance variables (attributes) via runtime proxies. This feature depends upon the entity class being non-final or else implementing an interface that declares all the attribute getters/setters. You can still persist final classes that do not implement such an interface with Hibernate, but you will not be able to use proxies for fetching lazy associations, therefore limiting your options for performance tuning. For the very same reason, you should also avoid declaring persistent attribute getters and setters as final.

Starting with 5.0, Hibernate offers a more robust version of bytecode enhancement as another means for handling lazy loading. Hibernate had some bytecode re-writing capabilities prior to 5.0 but they were very rudimentary. See the Bytecode Enhancement for additional information on fetching and on bytecode enhancement.

3.4.3. Implement a no-argument constructor

The entity class should have a no-argument constructor. Both Hibernate and Jakarta Persistence require this.

Jakarta Persistence requires that this constructor be defined as public or protected. Hibernate, for the most part, does not care about the constructor visibility, as long as the system SecurityManager allows overriding the visibility setting. That said, the constructor should be defined with at least package visibility if you wish to leverage runtime proxy generation.

3.4.4. Declare getters and setters for persistent attributes

The Jakarta Persistence specification requires this, otherwise, the model would prevent accessing the entity persistent state fields directly from outside the entity itself.

Although Hibernate does not require it, it is recommended to follow the JavaBean conventions and define getters and setters for entity persistent attributes. Nevertheless, you can still tell Hibernate to directly access the entity fields.

Attributes (whether fields or getters/setters) need not be declared public. Hibernate can deal with attributes declared with the public, protected, package or private visibility. Again, if wanting to use runtime proxy generation for lazy loading, the getter/setter should grant access to at least package visibility.

3.4.5. Providing identifier attribute(s)

Historically, providing identifier attributes was considered optional.

However, not defining identifier attributes on the entity should be considered a deprecated feature that will be removed in an upcoming release.

The identifier attribute does not necessarily need to be mapped to the column(s) that physically define the primary key. However, it should map to column(s) that can uniquely identify each row.

We recommend that you declare consistently-named identifier attributes on persistent classes and that you use a wrapper (i.e., non-primitive) type (e.g. Long or Integer).

The placement of the @Id annotation marks the persistence state access strategy.

Example 128. Identifier mapping
@Id
private Long id;

Hibernate offers multiple identifier generation strategies, see the Identifier Generators chapter for more about this topic.

3.4.6. Mapping the entity

The main piece in mapping the entity is the jakarta.persistence.Entity annotation.

The @Entity annotation defines just the name attribute which is used to give a specific entity name for use in JPQL queries.

By default, if the name attribute of the @Entity annotation is missing, the unqualified name of the entity class itself will be used as the entity name.

Because the entity name is given by the unqualified name of the class, Hibernate does not allow registering multiple entities with the same name even if the entity classes reside in different packages.

Without imposing this restriction, Hibernate would not know which entity class is referenced in a JPQL query if the unqualified entity name is associated with more then one entity classes.

In the following example, the entity name (e.g. Book) is given by the unqualified name of the entity class name.

Example 129. @Entity mapping with an implicit name
@Entity
public class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

However, the entity name can also be set explicitly as illustrated by the following example.

Example 130. @Entity mapping with an explicit name
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

An entity models a database table. The identifier uniquely identifies each row in that table. By default, the name of the table is assumed to be the same as the name of the entity. To explicitly give the name of the table or to specify other information about the table, we would use the jakarta.persistence.Table annotation.

Example 131. Simple @Entity with @Table
 @Entity(name = "Book")
 @Table(
         catalog = "public",
         schema = "store",
         name = "book"
)
 public static class Book {

     @Id
     private Long id;

     private String title;

     private String author;

     //Getters and setters are omitted for brevity
 }
Mapping the catalog of the associated table

Without specifying the catalog of the associated database table a given entity is mapped to, Hibernate will use the default catalog associated with the current database connection.

However, if your database hosts multiple catalogs, you can specify the catalog where a given table is located using the catalog attribute of the Jakarta Persistence @Table annotation.

Let’s assume we are using MySQL and want to map a Book entity to the book table located in the public catalog which looks as follows.

Example 132. The book table located in the public catalog
create table public.book (
  id bigint not null,
  author varchar(255),
  title varchar(255),
  primary key (id)
) engine=InnoDB

Now, to map the Book entity to the book table in the public catalog we can use the catalog attribute of the @Table Jakarta Persistence annotation.

Example 133. Specifying the database catalog using the @Table annotation
@Entity(name = "Book")
@Table(
	catalog = "public",
	name = "book"
)
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}
Mapping the schema of the associated table

Without specifying the schema of the associated database table a given entity is mapped to, Hibernate will use the default schema associated with the current database connection.

However, if your database supports schemas, you can specify the schema where a given table is located using the schema attribute of the Jakarta Persistence @Table annotation.

Let’s assume we are using PostgreSQL and want to map a Book entity to the book table located in the library schema which looks as follows.

Example 134. The book table located in the library schema
create table library.book (
  id int8 not null,
  author varchar(255),
  title varchar(255),
  primary key (id)
)

Now, to map the Book entity to the book table in the library schema we can use the schema attribute of the @Table Jakarta Persistence annotation.

Example 135. Specifying the database schema using the @Table annotation
@Entity(name = "Book")
@Table(
	schema = "library",
	name = "book"
)
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

The schema attribute of the @Table annotation works only if the underlying database supports schemas (e.g. PostgreSQL).

Therefore, if you’re using MySQL or MariaDB, which do not support schemas natively (schemas being just an alias for catalog), you need to use the catalog attribute, and not the schema one.

3.4.7. Implementing equals() and hashCode()

Much of the discussion in this section deals with the relation of an entity to a Hibernate Session, whether the entity is managed, transient or detached. If you are unfamiliar with these topics, they are explained in the Persistence Context chapter.

Whether to implement equals() and hashCode() methods in your domain model, let alone how to implement them, is a surprisingly tricky discussion when it comes to ORM.

There is really just one absolute case: a class that acts as an identifier must implement equals/hashCode based on the id value(s). Generally, this is pertinent for user-defined classes used as composite identifiers. Beyond this one very specific use case and few others we will discuss below, you may want to consider not implementing equals/hashCode altogether.

So what’s all the fuss? Normally, most Java objects provide a built-in equals() and hashCode() based on the object’s identity, so each new object will be different from all others. This is generally what you want in ordinary Java programming. Conceptually, however, this starts to break down when you start to think about the possibility of multiple instances of a class representing the same data.

This is, in fact, exactly the case when dealing with data coming from a database. Every time we load a specific Person from the database we would naturally get a unique instance. Hibernate, however, works hard to make sure that does not happen within a given Session. In fact, Hibernate guarantees equivalence of persistent identity (database row) and Java identity inside a particular session scope. So if we ask a Hibernate Session to load that specific Person multiple times we will actually get back the same instance:

Example 136. Scope of identity
Book book1 = entityManager.find(Book.class, 1L);
Book book2 = entityManager.find(Book.class, 1L);

assertTrue(book1 == book2);

Consider we have a Library parent entity which contains a java.util.Set of Book entities:

Example 137. Library entity mapping
@Entity(name = "Library")
public static class Library {

	@Id
	private Long id;

	private String name;

	@OneToMany(cascade = CascadeType.ALL)
	@JoinColumn(name = "book_id")
	private Set<Book> books = new HashSet<>();

	//Getters and setters are omitted for brevity
}
Example 138. Set usage with Session-scoped identity
Library library = entityManager.find(Library.class, 1L);

Book book1 = entityManager.find(Book.class, 1L);
Book book2 = entityManager.find(Book.class, 1L);

library.getBooks().add(book1);
library.getBooks().add(book2);

assertEquals(1, library.getBooks().size());

However, the semantic changes when we mix instances loaded from different Sessions:

Example 139. Mixed Sessions
Book book1 = doInJPA(this::entityManagerFactory, entityManager -> {
	return entityManager.find(Book.class, 1L);
});

Book book2 = doInJPA(this::entityManagerFactory, entityManager -> {
	return entityManager.find(Book.class, 1L);
});

assertFalse(book1 == book2);
doInJPA(this::entityManagerFactory, entityManager -> {
	Set<Book> books = new HashSet<>();

	books.add(book1);
	books.add(book2);

	assertEquals(2, books.size());
});

Specifically, the outcome in this last example will depend on whether the Book class implemented equals/hashCode, and, if so, how.

If the Book class did not override the default equals/hashCode, then the two Book object references are not going to be equal since their references are different.

Consider yet another case:

Example 140. Sets with transient entities
Library library = entityManager.find(Library.class, 1L);

Book book1 = new Book();
book1.setId(100L);
book1.setTitle("High-Performance Java Persistence");

Book book2 = new Book();
book2.setId(101L);
book2.setTitle("Java Persistence with Hibernate");

library.getBooks().add(book1);
library.getBooks().add(book2);

assertEquals(2, library.getBooks().size());

In cases where you will be dealing with entities outside of a Session (whether they be transient or detached), especially in cases where you will be using them in Java collections, you should consider implementing equals/hashCode.

A common initial approach is to use the entity’s identifier attribute as the basis for equals/hashCode calculations:

Example 141. Naive equals/hashCode implementation
@Entity(name = "Library")
public static class Library {

	@Id
	private Long id;

	private String name;

	@OneToMany(cascade = CascadeType.ALL)
	@JoinColumn(name = "book_id")
	private Set<Book> books = new HashSet<>();

	//Getters and setters are omitted for brevity
}

@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (!(o instanceof Book)) {
			return false;
		}
		Book book = (Book) o;
		return Objects.equals(id, book.getId());
	}

	@Override
	public int hashCode() {
		return Objects.hash(id);
	}
}

It turns out that this still breaks when adding transient instance of Book to a set as we saw in the last example:

Example 142. Auto-generated identifiers with Sets and naive equals/hashCode
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");

Book book2 = new Book();
book2.setTitle("Java Persistence with Hibernate");

Library library = doInJPA(this::entityManagerFactory, entityManager -> {
	Library _library = entityManager.find(Library.class, 1L);

	_library.getBooks().add(book1);
	_library.getBooks().add(book2);

	return _library;
});

assertFalse(library.getBooks().contains(book1));
assertFalse(library.getBooks().contains(book2));

The issue here is a conflict between the use of the generated identifier, the contract of Set, and the equals/hashCode implementations. Set says that the equals/hashCode value for an object should not change while the object is part of the Set. But that is exactly what happened here because the equals/hasCode are based on the (generated) id, which was not set until the Jakarta Persistence transaction is committed.

Note that this is just a concern when using generated identifiers. If you are using assigned identifiers this will not be a problem, assuming the identifier value is assigned prior to adding to the Set.

Another option is to force the identifier to be generated and set prior to adding to the Set:

Example 143. Forcing the flush before adding to the Set
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");

Book book2 = new Book();
book2.setTitle("Java Persistence with Hibernate");

Library library = doInJPA(this::entityManagerFactory, entityManager -> {
	Library _library = entityManager.find(Library.class, 1L);

	entityManager.persist(book1);
	entityManager.persist(book2);
	entityManager.flush();

	_library.getBooks().add(book1);
	_library.getBooks().add(book2);

	return _library;
});

assertTrue(library.getBooks().contains(book1));
assertTrue(library.getBooks().contains(book2));

But this is often not feasible.

The final approach is to use a "better" equals/hashCode implementation, making use of a natural-id or business-key.

Example 144. Natural Id equals/hashCode
@Entity(name = "Library")
public static class Library {

	@Id
	private Long id;

	private String name;

	@OneToMany(cascade = CascadeType.ALL)
	@JoinColumn(name = "book_id")
	private Set<Book> books = new HashSet<>();

	//Getters and setters are omitted for brevity
}

@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	@NaturalId
	private String isbn;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (!(o instanceof Book)) {
			return false;
		}
		Book book = (Book) o;
		return Objects.equals(isbn, book.getIsbn());
	}

	@Override
	public int hashCode() {
		return Objects.hash(isbn);
	}
}

This time, when adding a Book to the Library Set, you can retrieve the Book even after it’s being persisted:

Example 145. Natural Id equals/hashCode persist example
Book book1 = new Book();
book1.setTitle("High-Performance Java Persistence");
book1.setIsbn("978-9730228236");

Library library = doInJPA(this::entityManagerFactory, entityManager -> {
	Library _library = entityManager.find(Library.class, 1L);

	_library.getBooks().add(book1);

	return _library;
});

assertTrue(library.getBooks().contains(book1));

As you can see the question of equals/hashCode is not trivial, nor is there a one-size-fits-all solution.

Although using a natural-id is best for equals and hashCode, sometimes you only have the entity identifier that provides a unique constraint.

It’s possible to use the entity identifier for equality check, but it needs a workaround:

  • you need to provide a constant value for hashCode so that the hash code value does not change before and after the entity is flushed.

  • you need to compare the entity identifier equality only for non-transient entities.

For details on mapping the identifier, see the Identifiers chapter.

3.4.8. Mapping the entity to a SQL query

You can map an entity to a SQL query using the @Subselect annotation.

Example 146. @Subselect entity mapping
@Entity(name = "Client")
@Table(name = "client")
public static class Client {

	@Id
	private Long id;

	@Column(name = "first_name")
	private String firstName;

	@Column(name = "last_name")
	private String lastName;

	//Getters and setters omitted for brevity

}

@Entity(name = "Account")
@Table(name = "account")
public static class Account {

	@Id
	private Long id;

	@ManyToOne
	private Client client;

	private String description;

	//Getters and setters omitted for brevity

}

@Entity(name = "AccountTransaction")
@Table(name = "account_transaction")
public static class AccountTransaction {

	@Id
	@GeneratedValue
	private Long id;

	@ManyToOne
	private Account account;

	private Integer cents;

	private String description;

	//Getters and setters omitted for brevity

}

@Entity(name = "AccountSummary")
@Subselect(
	"select " +
	"	a.id as id, " +
	"	concat(concat(c.first_name, ' '), c.last_name) as clientName, " +
	"	sum(atr.cents) as balance " +
	"from account a " +
	"join client c on c.id = a.client_id " +
	"join account_transaction atr on a.id = atr.account_id " +
	"group by a.id, concat(concat(c.first_name, ' '), c.last_name)"
)
@Synchronize({"client", "account", "account_transaction"})
public static class AccountSummary {

	@Id
	private Long id;

	private String clientName;

	private int balance;

	//Getters and setters omitted for brevity

}

In the example above, the Account entity does not retain any balance since every account operation is registered as an AccountTransaction. To find the Account balance, we need to query the AccountSummary which shares the same identifier with the Account entity.

However, the AccountSummary is not mapped to a physical table, but to an SQL query.

So, if we have the following AccountTransaction record, the AccountSummary balance will match the proper amount of money in this Account.

Example 147. Finding a @Subselect entity
scope.inTransaction(
		(entityManager) -> {
			Client client = new Client();
			client.setId(1L);
			client.setFirstName("John");
			client.setLastName("Doe");
			entityManager.persist(client);

			Account account = new Account();
			account.setId(1L);
			account.setClient(client);
			account.setDescription("Checking account");
			entityManager.persist(account);

			AccountTransaction transaction = new AccountTransaction();
			transaction.setAccount(account);
			transaction.setDescription("Salary");
			transaction.setCents(100 * 7000);
			entityManager.persist(transaction);

			AccountSummary summary = entityManager.createQuery(
				"select s " +
				"from AccountSummary s " +
				"where s.id = :id", AccountSummary.class)
			.setParameter("id", account.getId())
			.getSingleResult();

			assertEquals("John Doe", summary.getClientName());
			assertEquals(100 * 7000, summary.getBalance());
		}
);

If we add a new AccountTransaction entity and refresh the AccountSummary entity, the balance is updated accordingly:

Example 148. Refreshing a @Subselect entity
scope.inTransaction(
		(entityManager) -> {
			AccountSummary summary = entityManager.find(AccountSummary.class, 1L);
			assertEquals("John Doe", summary.getClientName());
			assertEquals(100 * 7000, summary.getBalance());

			AccountTransaction transaction = new AccountTransaction();
			transaction.setAccount(entityManager.getReference(Account.class, 1L));
			transaction.setDescription("Shopping");
			transaction.setCents(-100 * 2200);
			entityManager.persist(transaction);
			entityManager.flush();

			entityManager.refresh(summary);
			assertEquals(100 * 4800, summary.getBalance());
		}
);

The goal of the @Synchronize annotation in the AccountSummary entity mapping is to instruct Hibernate which database tables are needed by the underlying @Subselect SQL query. This is because, unlike JPQL and HQL queries, Hibernate cannot parse the underlying native SQL query.

With the @Synchronize annotation in place, when executing an HQL or JPQL which selects from the AccountSummary entity, Hibernate will trigger a Persistence Context flush if there are pending Account, Client or AccountTransaction entity state transitions.

3.4.9. Define a custom entity proxy

By default, when it needs to use a proxy instead of the actual POJO, Hibernate is going to use a Bytecode manipulation library like Byte Buddy.

However, if the entity class is final, a proxy will not be created; you will get a POJO even when you only need a proxy reference. In this case, you could proxy an interface that this particular entity implements, as illustrated by the following example.

Example 149. Final entity class implementing the Identifiable interface
public interface Identifiable {

	Long getId();

	void setId(Long id);
}

@Entity(name = "Book")
@Proxy(proxyClass = Identifiable.class)
public static final class Book implements Identifiable {

	@Id
	private Long id;

	private String title;

	private String author;

	@Override
	public Long getId() {
		return id;
	}

	@Override
	public void setId(Long id) {
		this.id = id;
	}

	//Other getters and setters omitted for brevity
}

The @Proxy annotation is used to specify a custom proxy implementation for the current annotated entity.

When loading the Book entity proxy, Hibernate is going to proxy the Identifiable interface instead as illustrated by the following example:

Example 150. Proxying the final entity class implementing the Identifiable interface
doInHibernate(this::sessionFactory, session -> {
	Book book = new Book();
	book.setId(1L);
	book.setTitle("High-Performance Java Persistence");
	book.setAuthor("Vlad Mihalcea");

	session.persist(book);
});

doInHibernate(this::sessionFactory, session -> {
	Identifiable book = session.getReference(Book.class, 1L);

	assertTrue(
		"Loaded entity is not an instance of the proxy interface",
		book instanceof Identifiable
	);
	assertFalse(
		"Proxy class was not created",
		book instanceof Book
	);
});
insert
into
    Book
    (author, title, id)
values
    (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT]  - [1]

As you can see in the associated SQL snippet, Hibernate issues no SQL SELECT query since the proxy can be constructed without needing to fetch the actual entity POJO.

3.4.10. Define a custom entity persister

The @Persister annotation is used to specify a custom entity or collection persister.

For entities, the custom persister must implement the EntityPersister interface.

For collections, the custom persister must implement the CollectionPersister interface.

Supplying a custom persister has been allowed historically, but has never been fully supported. Hibernate 6 provides better, alternative ways to accomplish the use cases for a custom persister. As of 6.2 @Persister has been formally deprecated.
Example 151. Entity persister mapping
@Entity
@Persister(impl = EntityPersister.class)
public class Author {

    @Id
    public Integer id;

    @OneToMany(mappedBy = "author")
    @Persister(impl = CollectionPersister.class)
    public Set<Book> books = new HashSet<>();

    //Getters and setters omitted for brevity

    public void addBook(Book book) {
        this.books.add(book);
        book.setAuthor(this);
    }
}
@Entity
@Persister(impl = EntityPersister.class)
public class Book {

    @Id
    public Integer id;

    private String title;

    @ManyToOne(fetch = FetchType.LAZY)
    public Author author;

    //Getters and setters omitted for brevity
}

By providing your own EntityPersister and CollectionPersister implementations, you can control how entities and collections are persisted into the database.

3.5. Naming strategies

Part of the mapping of an object model to the relational database is mapping names from the object model to the corresponding database names. Hibernate looks at this as 2-stage process:

  • The first stage is determining a proper logical name from the domain model mapping. A logical name can be either explicitly specified by the user (e.g., using @Column or @Table) or it can be implicitly determined by Hibernate through an ImplicitNamingStrategy contract.

  • Second is the resolving of this logical name to a physical name which is defined by the PhysicalNamingStrategy contract.

Historical NamingStrategy contract

Historically Hibernate defined just a single org.hibernate.cfg.NamingStrategy. That singular NamingStrategy contract actually combined the separate concerns that are now modeled individually as ImplicitNamingStrategy and PhysicalNamingStrategy.

Also, the NamingStrategy contract was often not flexible enough to properly apply a given naming "rule", either because the API lacked the information to decide or because the API was honestly not well defined as it grew.

Due to these limitations, org.hibernate.cfg.NamingStrategy has been deprecated in favor of ImplicitNamingStrategy and PhysicalNamingStrategy.

At the core, the idea behind each naming strategy is to minimize the amount of repetitive information a developer must provide for mapping a domain model.

Jakarta Persistence Compatibility

Jakarta Persistence defines inherent rules about implicit logical name determination. If Jakarta Persistence provider portability is a major concern, or if you really just like the Jakarta Persistence-defined implicit naming rules, be sure to stick with ImplicitNamingStrategyJpaCompliantImpl (the default).

Also, Jakarta Persistence defines no separation between logical and physical name. Following the Jakarta Persistence specification, the logical name is the physical name. If Jakarta Persistence provider portability is important, applications should prefer not to specify a PhysicalNamingStrategy.

3.5.1. ImplicitNamingStrategy

When an entity does not explicitly name the database table that it maps to, we need to implicitly determine that table name. Or when a particular attribute does not explicitly name the database column that it maps to, we need to implicitly determine that column name. There are examples of the role of the org.hibernate.boot.model.naming.ImplicitNamingStrategy contract to determine a logical name when the mapping did not provide an explicit name.

Implicit Naming Strategy Diagram

Hibernate defines multiple ImplicitNamingStrategy implementations out-of-the-box. Applications are also free to plug in custom implementations.

There are multiple ways to specify the ImplicitNamingStrategy to use. First, applications can specify the implementation using the hibernate.implicit_naming_strategy configuration setting which accepts:

  • pre-defined "short names" for the out-of-the-box implementations

    default

    for org.hibernate.boot.model.naming.ImplicitNamingStrategyJpaCompliantImpl - an alias for jpa

    jpa

    for org.hibernate.boot.model.naming.ImplicitNamingStrategyJpaCompliantImpl - the Jakarta Persistence compliant naming strategy

    legacy-hbm

    for org.hibernate.boot.model.naming.ImplicitNamingStrategyLegacyHbmImpl - compliant with the original Hibernate NamingStrategy

    legacy-jpa

    for org.hibernate.boot.model.naming.ImplicitNamingStrategyLegacyJpaImpl - compliant with the legacy NamingStrategy developed for Java Persistence 1.0, which was unfortunately unclear in many respects regarding implicit naming rules

    component-path

    for org.hibernate.boot.model.naming.ImplicitNamingStrategyComponentPathImpl - mostly follows ImplicitNamingStrategyJpaCompliantImpl rules, except that it uses the full composite paths, as opposed to just the ending property part

  • reference to a Class that implements the org.hibernate.boot.model.naming.ImplicitNamingStrategy contract

  • FQN of a class that implements the org.hibernate.boot.model.naming.ImplicitNamingStrategy contract

Secondly, applications and integrations can leverage org.hibernate.boot.MetadataBuilder#applyImplicitNamingStrategy to specify the ImplicitNamingStrategy to use. See Bootstrap for additional details on bootstrapping.

3.5.2. PhysicalNamingStrategy

Many organizations define rules around the naming of database objects (tables, columns, foreign keys, etc). The idea of a PhysicalNamingStrategy is to help implement such naming rules without having to hard-code them into the mapping via explicit names.

While the purpose of an ImplicitNamingStrategy is to determine that an attribute named accountNumber maps to a logical column name of accountNumber when not explicitly specified, the purpose of a PhysicalNamingStrategy would be, for example, to say that the physical column name should instead be abbreviated to acct_num.

It is true that the resolution to acct_num could have been handled using an ImplicitNamingStrategy in this case.

But the point here is the separation of concerns. The PhysicalNamingStrategy will be applied regardless of whether the attribute explicitly specified the column name or whether we determined that implicitly. The ImplicitNamingStrategy would only be applied if an explicit name was not given. So, it all depends on needs and intent.

The default implementation is to simply use the logical name as the physical name. However applications and integrations can define custom implementations of this PhysicalNamingStrategy contract. Here is an example PhysicalNamingStrategy for a fictitious company named Acme Corp whose naming standards are to:

  • prefer underscore-delimited words rather than camel casing

  • replace certain words with standard abbreviations

Example 152. Example PhysicalNamingStrategy implementation
/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
 */
package org.hibernate.orm.test.naming;

import java.util.Arrays;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;

import org.hibernate.boot.model.naming.Identifier;
import org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl;
import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;

import org.junit.platform.commons.util.StringUtils;

/**
 * An example PhysicalNamingStrategy that implements database object naming standards
 * for our fictitious company Acme Corp.
 * <p>
 * In general Acme Corp prefers underscore-delimited words rather than camel casing.
 * <p>
 * Additionally standards call for the replacement of certain words with abbreviations.
 *
 * @author Steve Ebersole
 * @author Nathan Xu
 */
public class AcmeCorpPhysicalNamingStrategy extends PhysicalNamingStrategyStandardImpl {
	private static final Map<String, String> ABBREVIATIONS;

	static {
		ABBREVIATIONS = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
		ABBREVIATIONS.put("account", "acct");
		ABBREVIATIONS.put("number", "num");
	}

	@Override
	public Identifier toPhysicalTableName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
		final List<String> parts = splitAndReplace( logicalName.getText());
		return jdbcEnvironment.getIdentifierHelper().toIdentifier(
				String.join("_", parts),
				logicalName.isQuoted()
		);
	}

	@Override
	public Identifier toPhysicalSequenceName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
		final List<String> parts = splitAndReplace( logicalName.getText());
		// Acme Corp says all sequences should end with _seq
		if (!"seq".equals(parts.get(parts.size() - 1))) {
			parts.add("seq");
		}
		return jdbcEnvironment.getIdentifierHelper().toIdentifier(
				String.join("_", parts),
				logicalName.isQuoted()
		);
	}

	@Override
	public Identifier toPhysicalColumnName(Identifier logicalName, JdbcEnvironment jdbcEnvironment) {
		final List<String> parts = splitAndReplace( logicalName.getText());
		return jdbcEnvironment.getIdentifierHelper().toIdentifier(
				String.join("_", parts),
				logicalName.isQuoted()
		);
	}

	private List<String> splitAndReplace(String name) {
		return Arrays.stream(splitByCharacterTypeCamelCase(name))
				.filter(StringUtils::isNotBlank)
				.map(p -> ABBREVIATIONS.getOrDefault(p, p).toLowerCase(Locale.ROOT))
				.collect(Collectors.toList());
	}

	private String[] splitByCharacterTypeCamelCase(String s) {
		return s.split( "(?<!(^|[A-Z]))(?=[A-Z])|(?<!^)(?=[A-Z][a-z])" );
	}
}

There are multiple ways to specify the PhysicalNamingStrategy to use. First, applications can specify the implementation using the hibernate.physical_naming_strategy configuration setting which accepts:

  • reference to a Class that implements the org.hibernate.boot.model.naming.PhysicalNamingStrategy contract

  • FQN of a class that implements the org.hibernate.boot.model.naming.PhysicalNamingStrategy contract

Secondly, applications and integrations can leverage org.hibernate.boot.MetadataBuilder#applyPhysicalNamingStrategy. See Bootstrap for additional details on bootstrapping.

3.6. Access strategies

As a Jakarta Persistence provider, Hibernate can introspect both the entity attributes (instance fields) or the accessors (instance properties). By default, the placement of the @Id annotation gives the default access strategy. When placed on a field, Hibernate will assume field-based access. When placed on the identifier getter, Hibernate will use property-based access.

To avoid issues such as HCANN-63 - Property name beginning with at least two uppercase characters has odd functionality in HQL, you should pay attention to Java Bean specification in regard to naming properties.

Embeddable types inherit the access strategy from their parent entities.

3.6.1. Field-based access

Example 153. Field-based access
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

When using field-based access, adding other entity-level methods is much more flexible because Hibernate won’t consider those part of the persistence state. To exclude a field from being part of the entity persistent state, the field must be marked with the @Transient annotation.

Another advantage of using field-based access is that some entity attributes can be hidden from outside the entity.

An example of such attribute is the entity @Version field, which, usually, does not need to be manipulated by the data access layer.

With field-based access, we can simply omit the getter and the setter for this version field, and Hibernate can still leverage the optimistic concurrency control mechanism.

3.6.2. Property-based access

Example 154. Property-based access
@Entity(name = "Book")
public static class Book {

	private Long id;

	private String title;

	private String author;

	@Id
	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}
}

When using property-based access, Hibernate uses the accessors for both reading and writing the entity state. Every other method that will be added to the entity (e.g. helper methods for synchronizing both ends of a bidirectional one-to-many association) will have to be marked with the @Transient annotation.

3.6.3. Overriding the default access strategy

The default access strategy mechanism can be overridden with the Jakarta Persistence @Access annotation. In the following example, the @Version attribute is accessed by its field and not by its getter, like the rest of entity attributes.

Example 155. Overriding access strategy
@Entity(name = "Book")
public static class Book {

	private Long id;

	private String title;

	private String author;

	@Access(AccessType.FIELD)
	@Version
	private int version;

	@Id
	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}
}

3.6.4. Embeddable types and access strategy

Because embeddables are managed by their owning entities, the access strategy is therefore inherited from the entity too. This applies to both simple embeddable types as well as for collection of embeddables.

The embeddable types can overrule the default implicit access strategy (inherited from the owning entity). In the following example, the embeddable uses property-based access, no matter what access strategy the owning entity is choosing:

Example 156. Embeddable with exclusive access strategy
@Embeddable
@Access(AccessType.PROPERTY)
public static class Author {

	private String firstName;

	private String lastName;

	public Author() {
	}

	public Author(String firstName, String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
}

The owning entity can use field-based access while the embeddable uses property-based access as it has chosen explicitly:

Example 157. Entity including a single embeddable type
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	@Embedded
	private Author author;

	//Getters and setters are omitted for brevity
}

This works also for collection of embeddable types:

Example 158. Entity including a collection of embeddable types
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	@ElementCollection
	@CollectionTable(
		name = "book_author",
		joinColumns = @JoinColumn(name = "book_id")
	)
	private List<Author> authors = new ArrayList<>();

	//Getters and setters are omitted for brevity
}

3.7. Identifiers

Identifiers model the primary key of an entity. They are used to uniquely identify each specific entity.

Hibernate and Jakarta Persistence both make the following assumptions about the corresponding database column(s):

UNIQUE

The values must uniquely identify each row.

NOT NULL

The values cannot be null. For composite ids, no part can be null.

IMMUTABLE

The values, once inserted, can never be changed. In cases where the values for the PK you have chosen will be updated, Hibernate recommends mapping the mutable value as a natural id, and use a surrogate id for the PK. See Natural Ids.

Technically the identifier does not have to map to the column(s) physically defined as the table primary key. They just need to map to column(s) that uniquely identify each row. However, this documentation will continue to use the terms identifier and primary key interchangeably.

Every entity must define an identifier. For entity inheritance hierarchies, the identifier must be defined just on the entity that is the root of the hierarchy.

An identifier may be simple or composite.

3.7.1. Simple identifiers

Simple identifiers map to a single basic attribute, and are denoted using the jakarta.persistence.Id annotation.

According to Jakarta Persistence, only the following types are portably supported for use as identifier attribute types:

  • any Java primitive type

  • any primitive wrapper type

  • java.lang.String

  • java.util.Date (TemporalType#DATE)

  • java.sql.Date

  • java.math.BigDecimal

  • java.math.BigInteger

Hibernate, however, supports a more broad set of types to be used for identifiers (UUID, e.g.).

Assigned identifiers

Values for simple identifiers can be assigned, which simply means that the application itself will assign the value to the identifier attribute prior to persisting the entity.

Example 159. Simple assigned entity identifier
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}
Generated identifiers

Values for simple identifiers can be generated. To denote that an identifier attribute is generated, it is annotated with jakarta.persistence.GeneratedValue

Example 160. Simple generated identifier
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

When an entity with an identifier defined as generated is persisted, Hibernate will generate the value based on an associated generation strategy. Identifier value generations strategies are discussed in detail in the Generated identifier values section.

While Hibernate supports almost any valid basic type be used for generated identifier values, Jakarta Persistence restricts the allowable types to just integer types.

3.7.2. Composite identifiers

Composite identifiers correspond to one or more persistent attributes. Here are the rules governing composite identifiers, as defined by the Jakarta Persistence specification:

  • The composite identifier must be represented by a "primary key class". The primary key class may be defined using the jakarta.persistence.EmbeddedId annotation (see Composite identifiers with @EmbeddedId), or defined using the jakarta.persistence.IdClass annotation (see Composite identifiers with @IdClass).

  • The primary key class must be public and must have a public no-arg constructor.

  • The primary key class must be serializable.

  • The primary key class must define equals and hashCode methods, consistent with equality for the underlying database types to which the primary key is mapped.

The restriction that a composite identifier has to be represented by a "primary key class" (e.g. @EmbeddedId or @IdClass) is only Jakarta Persistence-specific.

Hibernate does allow composite identifiers to be defined without a "primary key class" via multiple @Id attributes, although that is generally considered poor design.

The attributes making up the composition can be either basic, composite or @ManyToOne. Note especially that collection and one-to-one are never appropriate.

3.7.3. Composite identifiers with @EmbeddedId

Modeling a composite identifier using an EmbeddedId simply means defining an embeddable to be a composition for the attributes making up the identifier, and then exposing an attribute of that embeddable type on the entity.

Example 161. Basic @EmbeddedId
@Entity(name = "SystemUser")
public static class SystemUser {

	@EmbeddedId
	private PK pk;

	private String name;

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class PK implements Serializable {

	private String subsystem;

	private String username;

	public PK(String subsystem, String username) {
		this.subsystem = subsystem;
		this.username = username;
	}

	private PK() {
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		PK pk = (PK) o;
		return Objects.equals(subsystem, pk.subsystem) &&
				Objects.equals(username, pk.username);
	}

	@Override
	public int hashCode() {
		return Objects.hash(subsystem, username);
	}
}

As mentioned before, EmbeddedIds can even contain @ManyToOne attributes:

Example 162. @EmbeddedId with @ManyToOne
@Entity(name = "SystemUser")
public static class SystemUser {

	@EmbeddedId
	private PK pk;

	private String name;

	//Getters and setters are omitted for brevity
}

@Entity(name = "Subsystem")
public static class Subsystem {

	@Id
	private String id;

	private String description;

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class PK implements Serializable {

	@ManyToOne(fetch = FetchType.LAZY)
	private Subsystem subsystem;

	private String username;

	public PK(Subsystem subsystem, String username) {
		this.subsystem = subsystem;
		this.username = username;
	}

	private PK() {
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		PK pk = (PK) o;
		return Objects.equals(subsystem, pk.subsystem) &&
				Objects.equals(username, pk.username);
	}

	@Override
	public int hashCode() {
		return Objects.hash(subsystem, username);
	}
}

Hibernate supports directly modeling @ManyToOne associations in the Primary Key class, whether @EmbeddedId or @IdClass.

However, that is not portably supported by the Jakarta Persistence specification. In Jakarta Persistence terms, one would use "derived identifiers". For more details, see Derived Identifiers.

3.7.4. Composite identifiers with @IdClass

Modeling a composite identifier using an IdClass differs from using an EmbeddedId in that the entity defines each individual attribute making up the composition. The IdClass is used as the representation of the identifier for load-by-id operations.

Example 163. Basic @IdClass
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {

	@Id
	private String subsystem;

	@Id
	private String username;

	private String name;

	public PK getId() {
		return new PK(
			subsystem,
			username
		);
	}

	public void setId(PK id) {
		this.subsystem = id.getSubsystem();
		this.username = id.getUsername();
	}

	//Getters and setters are omitted for brevity
}

public static class PK implements Serializable {

	private String subsystem;

	private String username;

	public PK(String subsystem, String username) {
		this.subsystem = subsystem;
		this.username = username;
	}

	private PK() {
	}

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		PK pk = (PK) o;
		return Objects.equals(subsystem, pk.subsystem) &&
				Objects.equals(username, pk.username);
	}

	@Override
	public int hashCode() {
		return Objects.hash(subsystem, username);
	}
}

Non-aggregated composite identifiers can also contain ManyToOne attributes as we saw with aggregated mappings, though still non-portably.

Example 164. IdClass with @ManyToOne
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {

	@Id
	@ManyToOne(fetch = FetchType.LAZY)
	private Subsystem subsystem;

	@Id
	private String username;

	private String name;

	//Getters and setters are omitted for brevity
}

@Entity(name = "Subsystem")
public static class Subsystem {

	@Id
	private String id;

	private String description;

	//Getters and setters are omitted for brevity
}

public static class PK implements Serializable {

	private Subsystem subsystem;

	private String username;

	public PK(Subsystem subsystem, String username) {
		this.subsystem = subsystem;
		this.username = username;
	}

	private PK() {
	}

	//Getters and setters are omitted for brevity
}

With non-aggregated composite identifiers, Hibernate also supports "partial" generation of the composite values.

Example 165. @IdClass with partial identifier generation using @GeneratedValue
@Entity(name = "SystemUser")
@IdClass(PK.class)
public static class SystemUser {

	@Id
	private String subsystem;

	@Id
	private String username;

	@Id
	@GeneratedValue
	private Integer registrationId;

	private String name;

	public PK getId() {
		return new PK(
			subsystem,
			username,
			registrationId
		);
	}

	public void setId(PK id) {
		this.subsystem = id.getSubsystem();
		this.username = id.getUsername();
		this.registrationId = id.getRegistrationId();
	}

	//Getters and setters are omitted for brevity
}

public static class PK implements Serializable {

	private String subsystem;

	private String username;

	private Integer registrationId;

	public PK(String subsystem, String username) {
		this.subsystem = subsystem;
		this.username = username;
	}

	public PK(String subsystem, String username, Integer registrationId) {
		this.subsystem = subsystem;
		this.username = username;
		this.registrationId = registrationId;
	}

	private PK() {
	}

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		PK pk = (PK) o;
		return Objects.equals(subsystem, pk.subsystem) &&
				Objects.equals(username, pk.username) &&
				Objects.equals(registrationId, pk.registrationId);
	}

	@Override
	public int hashCode() {
		return Objects.hash(subsystem, username, registrationId);
	}
}

This feature which allows auto-generated values in composite identifiers exists because of a highly questionable interpretation of the Jakarta Persistence specification made by the SpecJ committee.

Hibernate does not feel that Jakarta Persistence defines support for this, but added the feature simply to be usable in SpecJ benchmarks. Use of this feature may or may not be portable from a Jakarta Persistence perspective.

3.7.5. Composite identifiers with associations

Hibernate allows defining a composite identifier out of entity associations. In the following example, the Book entity identifier is formed of two @ManyToOne associations.

Example 166. Composite identifiers with associations
@Entity(name = "Book")
public static class Book implements Serializable {

	@Id
	@ManyToOne(fetch = FetchType.LAZY)
	private Author author;

	@Id
	@ManyToOne(fetch = FetchType.LAZY)
	private Publisher publisher;

	@Id
	private String title;

	public Book(Author author, Publisher publisher, String title) {
		this.author = author;
		this.publisher = publisher;
		this.title = title;
	}

	private Book() {
	}

	//Getters and setters are omitted for brevity


	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Book book = (Book) o;
		return Objects.equals(author, book.author) &&
				Objects.equals(publisher, book.publisher) &&
				Objects.equals(title, book.title);
	}

	@Override
	public int hashCode() {
		return Objects.hash(author, publisher, title);
	}
}

@Entity(name = "Author")
public static class Author implements Serializable {

	@Id
	private String name;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Author author = (Author) o;
		return Objects.equals(name, author.name);
	}

	@Override
	public int hashCode() {
		return Objects.hash(name);
	}
}

@Entity(name = "Publisher")
public static class Publisher implements Serializable {

	@Id
	private String name;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Publisher publisher = (Publisher) o;
		return Objects.equals(name, publisher.name);
	}

	@Override
	public int hashCode() {
		return Objects.hash(name);
	}
}

Although the mapping is much simpler than using an @EmbeddedId or an @IdClass, there’s no separation between the entity instance and the actual identifier. To query this entity, an instance of the entity itself must be supplied to the persistence context.

Example 167. Fetching with composite identifiers
Book book = entityManager.find(Book.class, new Book(
	author,
	publisher,
	"High-Performance Java Persistence"
));

assertEquals("Vlad Mihalcea", book.getAuthor().getName());

3.7.6. Composite identifiers with generated properties

When using composite identifiers, the underlying identifier properties must be manually assigned by the user.

Automatically generated properties are not supported to be used to generate the value of an underlying property that makes the composite identifier.

Therefore, you cannot use any of the automatic property generator described by the generated properties section like @Generated, @CreationTimestamp or @ValueGenerationType or database-generated values.

Nevertheless, you can still generate the identifier properties prior to constructing the composite identifier, as illustrated by the following examples.

Assuming we have the following EventId composite identifier and an Event entity which uses the aforementioned composite identifier.

Example 168. The Event entity and EventId composite identifier
@Entity
class Event {

    @Id
    private EventId id;

    @Column(name = "event_key")
    private String key;

    @Column(name = "event_value")
    private String value;

    //Getters and setters are omitted for brevity
}
@Embeddable
class EventId implements Serializable {

	private Integer category;

	private Timestamp createdOn;

	//Getters and setters are omitted for brevity
	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		EventId that = (EventId) o;
		return Objects.equals(category, that.category) &&
				Objects.equals(createdOn, that.createdOn);
	}

	@Override
	public int hashCode() {
		return Objects.hash(category, createdOn);
	}
}
In-memory generated composite identifier properties

If you want to generate the composite identifier properties in-memory, you need to do that as follows:

Example 169. In-memory generated composite identifier properties example
EventId id = new EventId();
id.setCategory(1);
id.setCreatedOn(new Timestamp(System.currentTimeMillis()));

Event event = new Event();
event.setId(id);
event.setKey("Temperature");
event.setValue("9");

entityManager.persist(event);

Notice that the createdOn property of the EventId composite identifier was generated by the data access code and assigned to the identifier prior to persisting the Event entity.

Database generated composite identifier properties

If you want to generate the composite identifier properties using a database function or stored procedure, you could to do it as illustrated by the following example.

Example 170. Database generated composite identifier properties example
OffsetDateTime currentTimestamp = (OffsetDateTime) entityManager
.createNativeQuery(
	"SELECT CURRENT_TIMESTAMP", OffsetDateTime.class)
.getSingleResult();

EventId id = new EventId();
id.setCategory(1);
id.setCreatedOn(Timestamp.from(currentTimestamp.toInstant()));

Event event = new Event();
event.setId(id);
event.setKey("Temperature");
event.setValue("9");

entityManager.persist(event);

Notice that the createdOn property of the EventId composite identifier was generated by calling the CURRENT_TIMESTAMP database function, and we assigned it to the composite identifier prior to persisting the Event entity.

3.7.7. Generated identifier values

Hibernate supports identifier value generation across a number of different types. Remember that Jakarta Persistence portably defines identifier value generation just for integer types.

You can also auto-generate values for non-identifier attributes. For more details, see the Generated properties section.

Identifier value generation is indicated using the jakarta.persistence.GeneratedValue annotation. The most important piece of information here is the specified jakarta.persistence.GenerationType which indicates how values will be generated.

AUTO (the default)

Indicates that the persistence provider (Hibernate) should choose an appropriate generation strategy. See Interpreting AUTO.

IDENTITY

Indicates that database IDENTITY columns will be used for primary key value generation. See Using IDENTITY columns.

SEQUENCE

Indicates that database sequence should be used for obtaining primary key values. See Using sequences.

TABLE

Indicates that a database table should be used for obtaining primary key values. See Using the table identifier generator.

3.7.8. Interpreting AUTO

How a persistence provider interprets the AUTO generation type is left up to the provider.

The default behavior is to look at the Java type of the identifier attribute, plus what the underlying database supports.

If the identifier type is UUID, Hibernate is going to use a UUID identifier.

If the identifier type is numeric (e.g. Long, Integer), then Hibernate will use its SequenceStyleGenerator which resolves to a SEQUENCE generation if the underlying database supports sequences and a table-based generation otherwise.

3.7.9. Using sequences

For implementing database sequence-based identifier value generation Hibernate makes use of its org.hibernate.id.enhanced.SequenceStyleGenerator id generator. It is important to note that SequenceStyleGenerator is capable of working against databases that do not support sequences by transparently switching to a table as the underlying backing, which gives Hibernate a huge degree of portability across databases while still maintaining consistent id generation behavior (versus say choosing between SEQUENCE and IDENTITY).

Example 171. Implicit sequence
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue( strategy = SEQUENCE )
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}

Notice that the mapping does not specify the name of the sequence to use. In such cases, Hibernate will assume a sequence name based on the name of the table to which the entity is mapped. Here, since the entity is mapped to a table named product, Hibernate will use a sequence named product_seq.

When using @Subselect mappings, using the "table name" is not valid so Hibernate falls back to using the entity name as the base along with the _seq suffix.

To specify the sequence name explicitly, the simplest form is to specify @GeneratedValue#generator.

Example 172. Named sequence
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = SEQUENCE,
		generator = "explicit_product_sequence"
	)
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}

For this mapping, Hibernate will use explicit_product_sequence as the name of the sequence.

For more advanced configuration, Jakarta Persistence defines the @SequenceGenerator annotation.

Example 173. Simple @SequenceGenerator
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = SEQUENCE,
		generator = "sequence-generator"
	)
	@SequenceGenerator(
		name = "sequence-generator",
		sequenceName = "explicit_product_sequence"
	)
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}

This is simply a more verbose form of the mapping in Named sequence. However, the jakarta.persistence.SequenceGenerator annotation allows you to specify additional configurations as well.

Example 174. Sequence configuration
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = GenerationType.SEQUENCE,
		generator = "sequence-generator"
	)
	@SequenceGenerator(
		name = "sequence-generator",
		sequenceName = "explicit_product_sequence",
		allocationSize = 5
	)
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}

Again the mapping specifies explicit_product_sequence as the physical sequence name, but it also specifies an explicit allocation-size ("increment by").

3.7.10. Using IDENTITY columns

For implementing identifier value generation based on IDENTITY columns, Hibernate makes use of its org.hibernate.id.IdentityGenerator id generator which expects the identifier to be generated by INSERT into the table. IdentityGenerator understands 3 different ways that the INSERT-generated value might be retrieved:

  • If Hibernate believes the JDBC environment supports java.sql.Statement#getGeneratedKeys, then that approach will be used for extracting the IDENTITY generated keys.

  • Otherwise, if Dialect#supportsInsertSelectIdentity reports true, Hibernate will use the Dialect specific INSERT+SELECT statement syntax.

  • Otherwise, Hibernate will expect that the database supports some form of asking for the most recently inserted IDENTITY value via a separate SQL command as indicated by Dialect#getIdentitySelectString.

It is important to realize that using IDENTITY columns imposes a runtime behavior where the entity row must be physically inserted prior to the identifier value being known.

This can mess up extended persistence contexts (long conversations). Because of the runtime imposition/inconsistency, Hibernate suggests other forms of identifier value generation be used (e.g. SEQUENCE) with extended contexts.

In Hibernate 5.3, Hibernate attempts to delay the insert of entities if the flush-mode does not equal AUTO. This was slightly problematic for entities that used IDENTITY or SEQUENCE generated identifiers that were also involved in some form of association with another entity in the same transaction.

In Hibernate 5.4, Hibernate attempts to remedy the problem using an algorithm to decide if the insert should be delayed or if it requires immediate insertion. We wanted to restore the behavior prior to 5.3 only for very specific use cases where it made sense.

Entity mappings can sometimes be complex and it is possible a corner case was overlooked. Hibernate offers a way to completely disable the 5.3 behavior in the event problems occur with DelayedPostInsertIdentifier. To enable the legacy behavior, set hibernate.id.disable_delayed_identity_inserts=true.

This configuration option is meant to act as a temporary fix and bridge the gap between the changes in this behavior across Hibernate 5.x releases. If this configuration setting is necessary for a mapping, please open a JIRA and report the mapping so that the algorithm can be reviewed.

There is yet another important runtime impact of choosing IDENTITY generation: Hibernate will not be able to batch INSERT statements for the entities using the IDENTITY generation.

The importance of this depends on the application-specific use cases. If the application is not usually creating many new instances of a given entity type using the IDENTITY generator, then this limitation will be less important since batching would not have been very helpful anyway.

3.7.11. Using the table identifier generator

Hibernate achieves table-based identifier generation based on its org.hibernate.id.enhanced.TableGenerator which defines a table capable of holding multiple named value segments for any number of entities.

The basic idea is that a given table-generator table (hibernate_sequences for example) can hold multiple segments of identifier generation values.

Example 175. Unnamed table generator
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = GenerationType.TABLE
	)
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}
create table hibernate_sequences (
    sequence_name varchar2(255 char) not null,
    next_val number(19,0),
    primary key (sequence_name)
)

If no table name is given Hibernate assumes an implicit name of hibernate_sequences.

Additionally, because no jakarta.persistence.TableGenerator#pkColumnValue is specified, Hibernate will use the default segment (sequence_name='default') from the hibernate_sequences table.

However, you can configure the table identifier generator using the @TableGenerator annotation.

Example 176. Configured table generator
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = GenerationType.TABLE,
		generator = "table-generator"
	)
	@TableGenerator(
		name =  "table-generator",
		table = "table_identifier",
		pkColumnName = "table_name",
		valueColumnName = "product_id",
		allocationSize = 5
	)
	private Long id;

	@Column(name = "product_name")
	private String name;

	//Getters and setters are omitted for brevity

}
create table table_identifier (
    table_name varchar2(255 char) not null,
    product_id number(19,0),
    primary key (table_name)
)

Now, when inserting 3 Product entities, Hibernate generates the following statements:

Example 177. Configured table generator persist example
for (long i = 1; i <= 3; i++) {
	Product product = new Product();
	product.setName(String.format("Product %d", i));
	entityManager.persist(product);
}
select
    tbl.product_id
from
    table_identifier tbl
where
    tbl.table_name = ?
for update

-- binding parameter [1] - [Product]

insert
into
    table_identifier
    (table_name, product_id)
values
    (?, ?)

-- binding parameter [1] - [Product]
-- binding parameter [2] - [1]

update
    table_identifier
set
    product_id= ?
where
    product_id= ?
    and table_name= ?

-- binding parameter [1] - [6]
-- binding parameter [2] - [1]

select
    tbl.product_id
from
    table_identifier tbl
where
    tbl.table_name= ? for update

update
    table_identifier
set
    product_id= ?
where
    product_id= ?
    and table_name= ?

-- binding parameter [1] - [11]
-- binding parameter [2] - [6]

insert
into
    Product
    (product_name, id)
values
    (?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 1]
-- binding parameter [2] as [BIGINT]  - [1]

insert
into
    Product
    (product_name, id)
values
    (?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 2]
-- binding parameter [2] as [BIGINT]  - [2]

insert
into
    Product
    (product_name, id)
values
    (?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 3]
-- binding parameter [2] as [BIGINT]  - [3]

3.7.12. Using UUID generation

As mentioned above, Hibernate supports UUID identifier value generation. This is supported through its org.hibernate.id.UUIDGenerator id generator.

NOTE

org.hibernate.id.UUIDGenerator is an example of @IdGeneratorType discussed in Using @IdGeneratorType

UUIDGenerator supports pluggable strategies for exactly how the UUID is generated. These strategies are defined by the org.hibernate.id.UUIDGenerationStrategy contract. The default strategy is a version 4 (random) strategy according to IETF RFC 4122. Hibernate does ship with an alternative strategy which is a RFC 4122 version 1 (time-based) strategy (using IP address rather than mac address).

Example 178. Implicitly using the random UUID strategy
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue
	private UUID id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

To specify an alternative generation strategy, we’d have to define some configuration via @GenericGenerator. Here we choose the RFC 4122 version 1 compliant strategy named org.hibernate.id.uuid.CustomVersionOneStrategy.

Example 179. Implicitly using the random UUID strategy
@Entity(name = "Book")
public static class Book {

	@Id
	@GeneratedValue(generator = "custom-uuid")
	@GenericGenerator(
		name = "custom-uuid",
		strategy = "org.hibernate.id.UUIDGenerator",
		parameters = {
			@Parameter(
				name = "uuid_gen_strategy_class",
				value = "org.hibernate.id.uuid.CustomVersionOneStrategy"
			)
		}
	)
	private UUID id;

	private String title;

	private String author;

	//Getters and setters are omitted for brevity
}

3.7.13. Optimizers

Most of the Hibernate generators that separately obtain identifier values from database structures support the use of pluggable optimizers. Optimizers help manage the number of times Hibernate has to talk to the database in order to generate identifier values. For example, with no optimizer applied to a sequence-generator, every time the application asked Hibernate to generate an identifier it would need to grab the next sequence value from the database. But if we can minimize the number of times we need to communicate with the database here, the application will be able to perform better, which is, in fact, the role of these optimizers.

none

No optimization is performed. We communicate with the database each and every time an identifier value is needed from the generator.

pooled-lo

The pooled-lo optimizer works on the principle that the increment-value is encoded into the database table/sequence structure. In sequence-terms, this means that the sequence is defined with a greater-than-1 increment size.

For example, consider a brand new sequence defined as create sequence m_sequence start with 1 increment by 20. This sequence essentially defines a "pool" of 20 usable id values each and every time we ask it for its next-value. The pooled-lo optimizer interprets the next-value as the low end of that pool.

So when we first ask it for next-value, we’d get 1. We then assume that the valid pool would be the values from 1-20 inclusive.

The next call to the sequence would result in 21, which would define 21-40 as the valid range. And so on. The "lo" part of the name indicates that the value from the database table/sequence is interpreted as the pool lo(w) end.

pooled

Just like pooled-lo, except that here the value from the table/sequence is interpreted as the high end of the value pool.

hilo; legacy-hilo

Define a custom algorithm for generating pools of values based on a single value from a table or sequence.

These optimizers are not recommended for use. They are maintained (and mentioned) here simply for use by legacy applications that used these strategies previously.

Applications can also implement and use their own optimizer strategies, as defined by the org.hibernate.id.enhanced.Optimizer contract.

3.7.14. Using @IdGeneratorType

@IdGeneratorType is a meta-annotation that allows the creation of custom annotations that support simple, concise and type-safe definition and configuration of custom org.hibernate.id.IdentifierGenerator implementations.

Example 180. @IdGeneratorType
public class CustomSequenceGenerator implements IdentifierGenerator {

	public CustomSequenceGenerator(
			Sequence config,
			Member annotatedMember,
			CustomIdGeneratorCreationContext context) {
		//...
	}

	@Override
	public Object generate(
			SharedSessionContractImplementor session,
			Object object) {
		//...
}

@IdGeneratorType( CustomSequenceGenerator.class )
@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface Sequence {
	String name();
	int startWith() default 1;
	int incrementBy() default 50;
	Class<? extends Optimizer> optimizer() default Optimizer.class;
}

The example illustrates using @IdGeneratorType to define a custom sequence-based annotation @Sequence to apply and configure a custom IdentifierGenerator implementation CustomSequenceGenerator.

Notice the CustomSequenceGenerator constructor. Custom generator defined through @IdGeneratorType receive the following arguments:

  1. The configuration annotation - here, @Sequence. This is the type-safety aspect, rather than relying on untyped configuration properties in a Map, etc.

  2. The Member to which annotation was applied. This allows access to the Java type of the identifier attribute, etc.

  3. CustomIdGeneratorCreationContext is a "parameter object" providing access to things often useful for identifier generators.

3.7.15. Using @GenericGenerator

@GenericGenerator is generally considered deprecated in favor of @IdGeneratorType

@GenericGenerator allows integration of any Hibernate org.hibernate.id.IdentifierGenerator implementation, including any of the specific ones discussed here and any custom ones.

Example 181. Pooled-lo optimizer mapping using @GenericGenerator mapping
@Entity(name = "Product")
public static class Product {

	@Id
	@GeneratedValue(
		strategy = GenerationType.SEQUENCE,
		generator = "product_generator"
	)
	@GenericGenerator(
		name = "product_generator",
		type = org.hibernate.id.enhanced.SequenceStyleGenerator.class,
		parameters = {
			@Parameter(name = "sequence_name", value = "product_sequence"),
			@Parameter(name = "initial_value", value = "1"),
			@Parameter(name = "increment_size", value = "3"),
			@Parameter(name = "optimizer", value = "pooled-lo")
		}
	)
	private Long id;

	@Column(name = "p_name")
	private String name;

	@Column(name = "p_number")
	private String number;

	//Getters and setters are omitted for brevity

}

Now, when saving 5 Person entities and flushing the Persistence Context after every 3 entities:

Example 182. Pooled-lo optimizer mapping using @GenericGenerator mapping
for (long i = 1; i <= 5; i++) {
	if(i % 3 == 0) {
		entityManager.flush();
	}
	Product product = new Product();
	product.setName(String.format("Product %d", i));
	product.setNumber(String.format("P_100_%d", i));
	entityManager.persist(product);
}
CALL NEXT VALUE FOR product_sequence

INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 1]
-- binding parameter [2] as [VARCHAR] - [P_100_1]
-- binding parameter [3] as [BIGINT]  - [1]

INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 2]
-- binding parameter [2] as [VARCHAR] - [P_100_2]
-- binding parameter [3] as [BIGINT]  - [2]

CALL NEXT VALUE FOR product_sequence

INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 3]
-- binding parameter [2] as [VARCHAR] - [P_100_3]
-- binding parameter [3] as [BIGINT]  - [3]

INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 4]
-- binding parameter [2] as [VARCHAR] - [P_100_4]
-- binding parameter [3] as [BIGINT]  - [4]

INSERT INTO Product (p_name, p_number, id)
VALUES (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Product 5]
-- binding parameter [2] as [VARCHAR] - [P_100_5]
-- binding parameter [3] as [BIGINT]  - [5]

As you can see from the list of generated SQL statements, you can insert 3 entities with just one database sequence call. This way, the pooled and the pooled-lo optimizers allow you to reduce the number of database roundtrips, therefore reducing the overall transaction response time.

3.7.16. Derived Identifiers

Java Persistence 2.0 added support for derived identifiers which allow an entity to borrow the identifier from a many-to-one or one-to-one association.

Example 183. Derived identifier with @MapsId
@Entity(name = "Person")
public static class Person  {

	@Id
	private Long id;

	@NaturalId
	private String registrationNumber;

	public Person() {}

	public Person(String registrationNumber) {
		this.registrationNumber = registrationNumber;
	}

	//Getters and setters are omitted for brevity
}

@Entity(name = "PersonDetails")
public static class PersonDetails  {

	@Id
	private Long id;

	private String nickName;

	@OneToOne
	@MapsId
	private Person person;

	//Getters and setters are omitted for brevity
}

In the example above, the PersonDetails entity uses the id column for both the entity identifier and for the one-to-one association to the Person entity. The value of the PersonDetails entity identifier is "derived" from the identifier of its parent Person entity.

Example 184. Derived identifier with @MapsId persist example
doInJPA(this::entityManagerFactory, entityManager -> {
	Person person = new Person("ABC-123");
	person.setId(1L);
	entityManager.persist(person);

	PersonDetails personDetails = new PersonDetails();
	personDetails.setNickName("John Doe");
	personDetails.setPerson(person);

	entityManager.persist(personDetails);
});

doInJPA(this::entityManagerFactory, entityManager -> {
	PersonDetails personDetails = entityManager.find(PersonDetails.class, 1L);

	assertEquals("John Doe", personDetails.getNickName());
});

The @MapsId annotation can also reference columns from an @EmbeddedId identifier as well.

The previous example can also be mapped using @PrimaryKeyJoinColumn.

Example 185. Derived identifier @PrimaryKeyJoinColumn
@Entity(name = "Person")
public static class Person  {

	@Id
	private Long id;

	@NaturalId
	private String registrationNumber;

	public Person() {}

	public Person(String registrationNumber) {
		this.registrationNumber = registrationNumber;
	}

	//Getters and setters are omitted for brevity
}

@Entity(name = "PersonDetails")
public static class PersonDetails  {

	@Id
	private Long id;

	private String nickName;

	@OneToOne
	@PrimaryKeyJoinColumn
	private Person person;

	public void setPerson(Person person) {
		this.person = person;
		this.id = person.getId();
	}

	//Other getters and setters are omitted for brevity
}

Unlike @MapsId, the application developer is responsible for ensuring that the entity identifier and the many-to-one (or one-to-one) association are in sync, as you can see in the PersonDetails#setPerson method.

3.7.17. @RowId

If you annotate a given entity with the @RowId annotation and the underlying database supports fetching a record by ROWID (e.g. Oracle), then Hibernate can use the ROWID pseudo-column for CRUD operations.

Example 186. @RowId entity mapping
@Entity(name = "Product")
@RowId("ROWID")
public static class Product {

	@Id
	private Long id;

	@Column(name = "`name`")
	private String name;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}

Now, when fetching an entity and modifying it, Hibernate uses the ROWID pseudo-column for the UPDATE SQL statement.

Example 187. @RowId example
Product product = entityManager.find(Product.class, 1L);

product.setName("Smart phone");
SELECT
    p.id as id1_0_0_,
    p."name" as name2_0_0_,
    p."number" as number3_0_0_,
    p.ROWID as rowid_0_
FROM
    Product p
WHERE
    p.id = ?

-- binding parameter [1] as [BIGINT] - [1]

-- extracted value ([name2_0_0_] : [VARCHAR]) - [Mobile phone]
-- extracted value ([number3_0_0_] : [VARCHAR]) - [123-456-7890]
-- extracted ROWID value: AAAwkBAAEAAACP3AAA

UPDATE
    Product
SET
    "name" = ?,
    "number" = ?
WHERE
    ROWID = ?

-- binding parameter [1] as [VARCHAR] - [Smart phone]
-- binding parameter [2] as [VARCHAR] - [123-456-7890]
-- binding parameter [3] as ROWID     - [AAAwkBAAEAAACP3AAA]

3.8. Associations

Associations describe how two or more entities form a relationship based on a database joining semantics.

3.8.1. @ManyToOne

@ManyToOne is the most common association, having a direct equivalent in the relational database as well (e.g. foreign key), and so it establishes a relationship between a child entity and a parent.

Example 188. @ManyToOne association
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	//Getters and setters are omitted for brevity

}

@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`number`")
	private String number;

	@ManyToOne
	@JoinColumn(name = "person_id",
			foreignKey = @ForeignKey(name = "PERSON_ID_FK")
	)
	private Person person;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    person_id BIGINT ,
    PRIMARY KEY ( id )
 )

ALTER TABLE Phone
ADD CONSTRAINT PERSON_ID_FK
FOREIGN KEY (person_id) REFERENCES Person

Each entity has a lifecycle of its own. Once the @ManyToOne association is set, Hibernate will set the associated database foreign key column.

Example 189. @ManyToOne association lifecycle
Person person = new Person();
entityManager.persist(person);

Phone phone = new Phone("123-456-7890");
phone.setPerson(person);
entityManager.persist(phone);

entityManager.flush();
phone.setPerson(null);
INSERT INTO Person ( id )
VALUES ( 1 )

INSERT INTO Phone ( number, person_id, id )
VALUES ( '123-456-7890', 1, 2 )

UPDATE Phone
SET    number = '123-456-7890',
       person_id = NULL
WHERE  id = 2

3.8.2. @OneToMany

The @OneToMany association links a parent entity with one or more child entities. If the @OneToMany doesn’t have a mirroring @ManyToOne association on the child side, the @OneToMany association is unidirectional. If there is a @ManyToOne association on the child side, the @OneToMany association is bidirectional and the application developer can navigate this relationship from both ends.

Unidirectional @OneToMany

When using a unidirectional @OneToMany association, Hibernate resorts to using a link table between the two joining entities.

Example 190. Unidirectional @OneToMany association
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person_Phone (
    Person_id BIGINT NOT NULL ,
    phones_id BIGINT NOT NULL
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    PRIMARY KEY ( id )
)

ALTER TABLE Person_Phone
ADD CONSTRAINT UK_9uhc5itwc9h5gcng944pcaslf
UNIQUE (phones_id)

ALTER TABLE Person_Phone
ADD CONSTRAINT FKr38us2n8g5p9rj0b494sd3391
FOREIGN KEY (phones_id) REFERENCES Phone

ALTER TABLE Person_Phone
ADD CONSTRAINT FK2ex4e4p7w1cj310kg2woisjl2
FOREIGN KEY (Person_id) REFERENCES Person

The @OneToMany association is by definition a parent association, regardless of whether it’s a unidirectional or a bidirectional one. Only the parent side of an association makes sense to cascade its entity state transitions to children.

Example 191. Cascading @OneToMany association
Person person = new Person();
Phone phone1 = new Phone("123-456-7890");
Phone phone2 = new Phone("321-654-0987");

person.getPhones().add(phone1);
person.getPhones().add(phone2);
entityManager.persist(person);
entityManager.flush();

person.getPhones().remove(phone1);
INSERT INTO Person
       ( id )
VALUES ( 1 )

INSERT INTO Phone
       ( number, id )
VALUES ( '123-456-7890', 2 )

INSERT INTO Phone
       ( number, id )
VALUES ( '321-654-0987', 3 )

INSERT INTO Person_Phone
       ( Person_id, phones_id )
VALUES ( 1, 2 )

INSERT INTO Person_Phone
       ( Person_id, phones_id )
VALUES ( 1, 3 )

DELETE FROM Person_Phone
WHERE  Person_id = 1

INSERT INTO Person_Phone
       ( Person_id, phones_id )
VALUES ( 1, 3 )

DELETE FROM Phone
WHERE  id = 2

When persisting the Person entity, the cascade will propagate the persist operation to the underlying Phone children as well. Upon removing a Phone from the phones collection, the association row is deleted from the link table, and the orphanRemoval attribute will trigger a Phone removal as well.

The unidirectional associations are not very efficient when it comes to removing child entities. In the example above, upon flushing the persistence context, Hibernate deletes all database rows from the link table (e.g. Person_Phone) that are associated with the parent Person entity and reinserts the ones that are still found in the @OneToMany collection.

On the other hand, a bidirectional @OneToMany association is much more efficient because the child entity controls the association.

Bidirectional @OneToMany

The bidirectional @OneToMany association also requires a @ManyToOne association on the child side. Although the Domain Model exposes two sides to navigate this association, behind the scenes, the relational database has only one foreign key for this relationship.

Every bidirectional association must have one owning side only (the child side), the other one being referred to as the inverse (or the mappedBy) side.

Example 192. @OneToMany association mappedBy the @ManyToOne side
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

	public void addPhone(Phone phone) {
		phones.add(phone);
		phone.setPerson(this);
	}

	public void removePhone(Phone phone) {
		phones.remove(phone);
		phone.setPerson(null);
	}
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@NaturalId
	@Column(name = "`number`", unique = true)
	private String number;

	@ManyToOne
	private Person person;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    person_id BIGINT ,
    PRIMARY KEY ( id )
)

ALTER TABLE Phone
ADD CONSTRAINT UK_l329ab0g4c1t78onljnxmbnp6
UNIQUE (number)

ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEY (person_id) REFERENCES Person

Whenever a bidirectional association is formed, the application developer must make sure both sides are in-sync at all times.

The addPhone() and removePhone() are utility methods that synchronize both ends whenever a child element is added or removed.

Because the Phone class has a @NaturalId column (the phone number being unique), the equals() and the hashCode() can make use of this property, and so the removePhone() logic is reduced to the remove() Java Collection method.

Example 193. Bidirectional @OneToMany with an owner @ManyToOne side lifecycle
Person person = new Person();
Phone phone1 = new Phone("123-456-7890");
Phone phone2 = new Phone("321-654-0987");

person.addPhone(phone1);
person.addPhone(phone2);
entityManager.persist(person);
entityManager.flush();

person.removePhone(phone1);
INSERT INTO Person
       ( id )
VALUES ( 1 )

INSERT INTO Phone
       ( "number", person_id, id )
VALUES ( '123-456-7890', 1, 2 )

INSERT INTO Phone
       ( "number", person_id, id )
VALUES ( '321-654-0987', 1, 3 )

DELETE FROM Phone
WHERE  id = 2

Unlike the unidirectional @OneToMany, the bidirectional association is much more efficient when managing the collection persistence state. Every element removal only requires a single update (in which the foreign key column is set to NULL), and, if the child entity lifecycle is bound to its owning parent so that the child cannot exist without its parent, then we can annotate the association with the orphanRemoval attribute and dissociating the child will trigger a delete statement on the actual child table row as well.

3.8.3. @OneToOne

The @OneToOne association can either be unidirectional or bidirectional. A unidirectional association follows the relational database foreign key semantics, the client-side owning the relationship. A bidirectional association features a mappedBy @OneToOne parent side too.

Unidirectional @OneToOne
Example 194. Unidirectional @OneToOne
@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`number`")
	private String number;

	@OneToOne
	@JoinColumn(name = "details_id")
	private PhoneDetails details;

	//Getters and setters are omitted for brevity

}

@Entity(name = "PhoneDetails")
public static class PhoneDetails {

	@Id
	@GeneratedValue
	private Long id;

	private String provider;

	private String technology;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    details_id BIGINT ,
    PRIMARY KEY ( id )
)

CREATE TABLE PhoneDetails (
    id BIGINT NOT NULL ,
    provider VARCHAR(255) ,
    technology VARCHAR(255) ,
    PRIMARY KEY ( id )
)

ALTER TABLE Phone
ADD CONSTRAINT FKnoj7cj83ppfqbnvqqa5kolub7
FOREIGN KEY (details_id) REFERENCES PhoneDetails

From a relational database point of view, the underlying schema is identical to the unidirectional @ManyToOne association, as the client-side controls the relationship based on the foreign key column.

But then, it’s unusual to consider the Phone as a client-side and the PhoneDetails as the parent-side because the details cannot exist without an actual phone. A much more natural mapping would be the Phone were the parent-side, therefore pushing the foreign key into the PhoneDetails table. This mapping requires a bidirectional @OneToOne association as you can see in the following example:

Bidirectional @OneToOne
Example 195. Bidirectional @OneToOne
@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`number`")
	private String number;

	@OneToOne(
		mappedBy = "phone",
		cascade = CascadeType.ALL,
		orphanRemoval = true,
		fetch = FetchType.LAZY
	)
	private PhoneDetails details;

	//Getters and setters are omitted for brevity

	public void addDetails(PhoneDetails details) {
		details.setPhone(this);
		this.details = details;
	}

	public void removeDetails() {
		if (details != null) {
			details.setPhone(null);
			this.details = null;
		}
	}
}

@Entity(name = "PhoneDetails")
public static class PhoneDetails {

	@Id
	@GeneratedValue
	private Long id;

	private String provider;

	private String technology;

	@OneToOne(fetch = FetchType.LAZY)
	@JoinColumn(name = "phone_id")
	private Phone phone;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE PhoneDetails (
    id BIGINT NOT NULL ,
    provider VARCHAR(255) ,
    technology VARCHAR(255) ,
    phone_id BIGINT ,
    PRIMARY KEY ( id )
)

ALTER TABLE PhoneDetails
ADD CONSTRAINT FKeotuev8ja8v0sdh29dynqj05p
FOREIGN KEY (phone_id) REFERENCES Phone

This time, the PhoneDetails owns the association, and, like any bidirectional association, the parent-side can propagate its lifecycle to the child-side through cascading.

Example 196. Bidirectional @OneToOne lifecycle
Phone phone = new Phone("123-456-7890");
PhoneDetails details = new PhoneDetails("T-Mobile", "GSM");

phone.addDetails(details);
entityManager.persist(phone);
INSERT INTO Phone ( number, id )
VALUES ( '123-456-7890', 1 )

INSERT INTO PhoneDetails ( phone_id, provider, technology, id )
VALUES ( 1, 'T-Mobile', 'GSM', 2 )

When using a bidirectional @OneToOne association, Hibernate enforces the unique constraint upon fetching the child-side. If there are more than one children associated with the same parent, Hibernate will throw a org.hibernate.exception.ConstraintViolationException. Continuing the previous example, when adding another PhoneDetails, Hibernate validates the uniqueness constraint when reloading the Phone object.

Example 197. Bidirectional @OneToOne unique constraint
PhoneDetails otherDetails = new PhoneDetails("T-Mobile", "CDMA");
otherDetails.setPhone(phone);
entityManager.persist(otherDetails);
entityManager.flush();
entityManager.clear();

//throws jakarta.persistence.PersistenceException: org.hibernate.HibernateException: More than one row with the given identifier was found: 1
phone = entityManager.find(Phone.class, phone.getId());
Bidirectional @OneToOne lazy association

Although you might annotate the parent-side association to be fetched lazily, Hibernate cannot honor this request since it cannot know whether the association is null or not.

The only way to figure out whether there is an associated record on the child side is to fetch the child association using a secondary query. Because this can lead to N+1 query issues, it’s much more efficient to use unidirectional @OneToOne associations with the @MapsId annotation in place.

However, if you really need to use a bidirectional association and want to make sure that this is always going to be fetched lazily, then you need to enable lazy state initialization bytecode enhancement.

Example 198. Bidirectional @OneToOne lazy parent-side association
@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`number`")
	private String number;

	@OneToOne(
		mappedBy = "phone",
		cascade = CascadeType.ALL,
		orphanRemoval = true,
		fetch = FetchType.LAZY
	)
	private PhoneDetails details;

	//Getters and setters are omitted for brevity

	public void addDetails(PhoneDetails details) {
		details.setPhone(this);
		this.details = details;
	}

	public void removeDetails() {
		if (details != null) {
			details.setPhone(null);
			this.details = null;
		}
	}
}

@Entity(name = "PhoneDetails")
public static class PhoneDetails {

	@Id
	@GeneratedValue
	private Long id;

	private String provider;

	private String technology;

	@OneToOne(fetch = FetchType.LAZY)
	@JoinColumn(name = "phone_id")
	private Phone phone;

	//Getters and setters are omitted for brevity

}

For more about how to enable Bytecode enhancement, see the Bytecode Enhancement chapter.

3.8.4. @ManyToMany

The @ManyToMany association requires a link table that joins two entities. Like the @OneToMany association, @ManyToMany can be either unidirectional or bidirectional.

Unidirectional @ManyToMany
Example 199. Unidirectional @ManyToMany
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
	private List<Address> addresses = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Address")
public static class Address {

	@Id
	@GeneratedValue
	private Long id;

	private String street;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Address (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    street VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person_Address (
    Person_id BIGINT NOT NULL ,
    addresses_id BIGINT NOT NULL
)

ALTER TABLE Person_Address
ADD CONSTRAINT FKm7j0bnabh2yr0pe99il1d066u
FOREIGN KEY (addresses_id) REFERENCES Address

ALTER TABLE Person_Address
ADD CONSTRAINT FKba7rc9qe2vh44u93u0p2auwti
FOREIGN KEY (Person_id) REFERENCES Person

Just like with unidirectional @OneToMany associations, the link table is controlled by the owning side.

When an entity is removed from the @ManyToMany collection, Hibernate simply deletes the joining record in the link table. Unfortunately, this operation requires removing all entries associated with a given parent and recreating the ones that are listed in the current running persistent context.

Example 200. Unidirectional @ManyToMany lifecycle
Person person1 = new Person();
Person person2 = new Person();

Address address1 = new Address("12th Avenue", "12A");
Address address2 = new Address("18th Avenue", "18B");

person1.getAddresses().add(address1);
person1.getAddresses().add(address2);

person2.getAddresses().add(address1);

entityManager.persist(person1);
entityManager.persist(person2);

entityManager.flush();

person1.getAddresses().remove(address1);
INSERT INTO Person ( id )
VALUES ( 1 )

INSERT INTO Address ( number, street, id )
VALUES ( '12A', '12th Avenue', 2 )

INSERT INTO Address ( number, street, id )
VALUES ( '18B', '18th Avenue', 3 )

INSERT INTO Person ( id )
VALUES ( 4 )

INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 2 )
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 3 )
INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 4, 2 )

DELETE FROM Person_Address
WHERE  Person_id = 1

INSERT INTO Person_Address ( Person_id, addresses_id )
VALUES ( 1, 3 )

For @ManyToMany associations, the REMOVE entity state transition doesn’t make sense to be cascaded because it will propagate beyond the link table. Since the other side might be referenced by other entities on the parent-side, the automatic removal might end up in a ConstraintViolationException.

For example, if @ManyToMany(cascade = CascadeType.ALL) was defined and the first person would be deleted, Hibernate would throw an exception because another person is still associated with the address that’s being deleted.

Person person1 = entityManager.find(Person.class, personId);
entityManager.remove(person1);

Caused by: jakarta.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: could not execute statement
Caused by: org.hibernate.exception.ConstraintViolationException: could not execute statement
Caused by: java.sql.SQLIntegrityConstraintViolationException: integrity constraint violation: foreign key no action; FKM7J0BNABH2YR0PE99IL1D066U table: PERSON_ADDRESS

By simply removing the parent-side, Hibernate can safely remove the associated link records as you can see in the following example:

Example 201. Unidirectional @ManyToMany entity removal
Person person1 = entityManager.find(Person.class, personId);
entityManager.remove(person1);
DELETE FROM Person_Address
WHERE  Person_id = 1

DELETE FROM Person
WHERE  id = 1
Bidirectional @ManyToMany

A bidirectional @ManyToMany association has an owning and a mappedBy side. To preserve synchronicity between both sides, it’s good practice to provide helper methods for adding or removing child entities.

Example 202. Bidirectional @ManyToMany
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@NaturalId
	private String registrationNumber;

	@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
	private List<Address> addresses = new ArrayList<>();

	//Getters and setters are omitted for brevity

	public void addAddress(Address address) {
		addresses.add(address);
		address.getOwners().add(this);
	}

	public void removeAddress(Address address) {
		addresses.remove(address);
		address.getOwners().remove(this);
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Person person = (Person) o;
		return Objects.equals(registrationNumber, person.registrationNumber);
	}

	@Override
	public int hashCode() {
		return Objects.hash(registrationNumber);
	}
}

@Entity(name = "Address")
public static class Address {

	@Id
	@GeneratedValue
	private Long id;

	private String street;

	@Column(name = "`number`")
	private String number;

	private String postalCode;

	@ManyToMany(mappedBy = "addresses")
	private List<Person> owners = new ArrayList<>();

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Address address = (Address) o;
		return Objects.equals(street, address.street) &&
				Objects.equals(number, address.number) &&
				Objects.equals(postalCode, address.postalCode);
	}

	@Override
	public int hashCode() {
		return Objects.hash(street, number, postalCode);
	}
}
CREATE TABLE Address (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    postalCode VARCHAR(255) ,
    street VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person (
    id BIGINT NOT NULL ,
    registrationNumber VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person_Address (
    owners_id BIGINT NOT NULL ,
    addresses_id BIGINT NOT NULL
)

ALTER TABLE Person
ADD CONSTRAINT UK_23enodonj49jm8uwec4i7y37f
UNIQUE (registrationNumber)

ALTER TABLE Person_Address
ADD CONSTRAINT FKm7j0bnabh2yr0pe99il1d066u
FOREIGN KEY (addresses_id) REFERENCES Address

ALTER TABLE Person_Address
ADD CONSTRAINT FKbn86l24gmxdv2vmekayqcsgup
FOREIGN KEY (owners_id) REFERENCES Person

With the helper methods in place, the synchronicity management can be simplified, as you can see in the following example:

Example 203. Bidirectional @ManyToMany lifecycle
Person person1 = new Person("ABC-123");
Person person2 = new Person("DEF-456");

Address address1 = new Address("12th Avenue", "12A", "4005A");
Address address2 = new Address("18th Avenue", "18B", "4007B");

person1.addAddress(address1);
person1.addAddress(address2);

person2.addAddress(address1);

entityManager.persist(person1);
entityManager.persist(person2);

entityManager.flush();

person1.removeAddress(address1);
INSERT INTO Person ( registrationNumber, id )
VALUES ( 'ABC-123', 1 )

INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '12A', '4005A', '12th Avenue', 2 )

INSERT INTO Address ( number, postalCode, street, id )
VALUES ( '18B', '4007B', '18th Avenue', 3 )

INSERT INTO Person ( registrationNumber, id )
VALUES ( 'DEF-456', 4 )

INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 2 )

INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 3 )

INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 4, 2 )

DELETE FROM Person_Address
WHERE  owners_id = 1

INSERT INTO Person_Address ( owners_id, addresses_id )
VALUES ( 1, 3 )

If a bidirectional @OneToMany association performs better when removing or changing the order of child elements, the @ManyToMany relationship cannot benefit from such an optimization because the foreign key side is not in control. To overcome this limitation, the link table must be directly exposed and the @ManyToMany association split into two bidirectional @OneToMany relationships.

To most natural @ManyToMany association follows the same logic employed by the database schema, and the link table has an associated entity which controls the relationship for both sides that need to be joined.

Both the Person and the Address have a mappedBy @OneToMany side, while the PersonAddress owns the person and the address @ManyToOne associations. Because this mapping is formed out of two bidirectional associations, the helper methods are even more relevant.

The aforementioned example uses a Hibernate-specific mapping for the link entity since Jakarta Persistence doesn’t allow building a composite identifier out of multiple @ManyToOne associations.

For more details, see the composite identifiers with associations section.

The entity state transitions are better managed than in the previous bidirectional @ManyToMany case.

There is only one delete statement executed because, this time, the association is controlled by the @ManyToOne side which only has to monitor the state of the underlying foreign key relationship to trigger the right DML statement.

3.8.5. @NotFound

When dealing with associations which are not enforced by a physical foreign-key, it is possible for a non-null foreign-key value to point to a non-existent value on the associated entity’s table.

Not enforcing physical foreign-keys at the database level is highly discouraged.

Hibernate provides support for such models using the @NotFound annotation, which accepts a NotFoundAction value which indicates how Hibernate should behave when such broken foreign-keys are encountered -

EXCEPTION

(default) Hibernate will throw an exception (FetchNotFoundException)

IGNORE

the association will be treated as null

Both @NotFound(IGNORE) and @NotFound(EXCEPTION) cause Hibernate to assume that there is no physical foreign-key.

@ManyToOne and @OneToOne associations annotated with @NotFound are always fetched eagerly even if the fetch strategy is set to FetchType.LAZY.

If the application itself manages the referential integrity and can guarantee that there are no broken foreign-keys, jakarta.persistence.ForeignKey(NO_CONSTRAINT) can be used instead. This will force Hibernate to not export physical foreign-keys, but still behave as if there is in terms of avoiding the downsides to @NotFound.

Considering the following City and Person entity mappings:

Example 206. @NotFound mapping example
@Entity(name = "Person")
@Table(name = "Person")
public static class Person {

	@Id
	private Integer id;
	private String name;

	@ManyToOne
	@NotFound(action = NotFoundAction.IGNORE)
	@JoinColumn(name = "city_fk", referencedColumnName = "id")
	private City city;

	//Getters and setters are omitted for brevity

}

@Entity(name = "City")
@Table(name = "City")
public static class City implements Serializable {

	@Id
	private Integer id;

	private String name;

	//Getters and setters are omitted for brevity

}

If we have the following entities in our database:

Example 207. @NotFound persist example
City newYork = new City( 1, "New York" );
entityManager.persist( newYork );

Person person = new Person( 1, "John Doe", newYork );
entityManager.persist( person );

When loading the Person entity, Hibernate is able to locate the associated City parent entity:

Example 208. @NotFound - find existing entity example
Person person = entityManager.find( Person.class, 1 );
assertEquals( "New York", person.getCity().getName() );

However, if we break the foreign-key:

Example 209. Break the foreign-key
// the database allows this because there is no physical foreign-key
entityManager.createQuery( "delete City" ).executeUpdate();

Hibernate is not going to throw any exception, and it will assign a value of null for the non-existing City entity reference:

Example 210. @NotFound - find non-existing City example
Person person = entityManager.find( Person.class, 1 );

assertNull( person.getCity(), "person.getCity() should be null" );

@NotFound also affects how the association is treated as "implicit joins" in HQL and Criteria. When there is a physical foreign-key, Hibernate can safely assume that the value in the foreign-key’s key-column(s) will match the value in the target-column(s) because the database makes sure that is the case. However, @NotFound forces Hibernate to perform a physical join for implicit joins when it might not be needed otherwise.

Using the Person / City model, consider the query from Person p where p.city.id is null.

Normally Hibernate would not need the join between the Person table and the City table because a physical foreign-key would ensure that any non-null value in the Person.cityName column has a matching non-null value in the City.name column.

However, with @NotFound mappings it is possible to have a broken association because there is no physical foreign-key enforcing the relation. As seen in Break the foreign-key, the Person.cityName column for John Doe has been changed from "New York" to "Atlantis" even though there is no City in the database named "Atlantis". Hibernate is not able to trust the referring foreign-key value ("Atlantis") has a matching target value, so it must join to the City table to resolve the city.id value.

Example 211. Implicit join example
final List<Person> nullResults = entityManager
		.createQuery( "from Person p where p.city.id is null", Person.class )
		.getResultList();
assertThat( nullResults ).isEmpty();

final List<Person> nonNullResults = entityManager
		.createQuery( "from Person p where p.city.id is not null", Person.class )
		.getResultList();
assertThat( nonNullResults ).isEmpty();

Neither result includes a match for "John Doe" because the inner-join filters out that row.

Hibernate does support a means to refer specifically to the key column (Person.cityName) in a query using the special fk(..) function. E.g.

Example 212. Implicit join example
final List<String> nullResults = entityManager
		.createQuery( "select p.name from Person p where fk( p.city ) is null", String.class )
		.getResultList();

assertThat( nullResults ).isEmpty();

final List<String> nonNullResults = entityManager
		.createQuery( "select p.name from Person p where fk( p.city ) is not null", String.class )
		.getResultList();
assertThat( nonNullResults ).hasSize( 1 );
assertThat( nonNullResults.get( 0 ) ).isEqualTo( "John Doe" );

3.8.6. @Any mapping

The @Any mapping is useful to emulate a unidirectional @ManyToOne association when there can be multiple target entities.

Because the @Any mapping defines a polymorphic association to classes from multiple tables, this association type requires the FK column which provides the associated parent identifier and a metadata information for the associated entity type.

This is not the usual way of mapping polymorphic associations and you should use this only in special cases (e.g. audit logs, user session data, etc).

To map such an association, Hibernate needs to understand 3 things:

  1. The column and mapping for the discriminator

  2. The column and mapping for the key

  3. The mapping between discriminator values and entity classes

The discriminator

The discriminator of an any-style association holds the value that indicates which entity is referred to by a row.

Its "column" can be specified with either @Column or @Formula. The mapping type can be influenced by any of:

  1. @AnyDiscriminator allows re-using the DiscriminatorType simplified mappings from Jakarta Persistence for the common cases

  2. @JavaType

  3. @JdbcType

  4. @JdbcTypeCode

The key

The key of an any-style association holds the matching key for the row

Its "column" can be specified with either @JoinColumn (@JoinFormula not supported). The mapping type can be influenced by any of:

  1. @AnyKeyJavaClass

  2. @AnyKeyJavaType

  3. @AnyKeyJdbcType

  4. @AnyKeyJdbcTypeCode

The discriminator value mappings

@AnyDiscriminatorValue is used to map the discriminator values to the corresponding entity classes

3.8.7. Example using @Any mapping

For this example, consider the following Property class hierarchy:

Example 213. Property class hierarchy
public interface Property<T> {

    String getName();

    T getValue();
}


@Entity
@Table(name="integer_property")
public class IntegerProperty implements Property<Integer> {

    @Id
    private Long id;

    @Column(name = "`name`")
    private String name;

    @Column(name = "`value`")
    private Integer value;

    @Override
    public String getName() {
        return name;
    }

    @Override
    public Integer getValue() {
        return value;
    }

    //Getters and setters omitted for brevity
}


@Entity
@Table(name="string_property")
public class StringProperty implements Property<String> {

    @Id
    private Long id;

    @Column(name = "`name`")
    private String name;

    @Column(name = "`value`")
    private String value;

    @Override
    public String getName() {
        return name;
    }

    @Override
    public String getValue() {
        return value;
    }

    //Getters and setters omitted for brevity
}

A PropertyHolder entity defines an attribute of type Property:

Example 214. @Any mapping usage
@Entity
@Table(name = "property_holder")
public class PropertyHolder {

    @Id
    private Long id;

    @Any
    @AnyDiscriminator(DiscriminatorType.STRING)
    @AnyDiscriminatorValue(discriminator = "S", entity = StringProperty.class)
    @AnyDiscriminatorValue(discriminator = "I", entity = IntegerProperty.class)
    @AnyKeyJavaClass(Long.class)
    @Column(name = "property_type")
    @JoinColumn(name = "property_id")
    private Property property;

    //Getters and setters are omitted for brevity

}
CREATE TABLE property_holder (
    id BIGINT NOT NULL,
    property_type VARCHAR(255),
    property_id BIGINT,
    PRIMARY KEY ( id )
)

PropertyHolder#property can refer to either StringProperty or IntegerProperty references, as indicated by the associated discriminator according to the @DiscriminatorValue annotations.

As you can see, there are two columns used to reference a Property instance: property_id and property_type. The property_id is used to match the id column of either the string_property or integer_property tables, while the property_type is used to match the string_property or the integer_property table.

To see the @Any annotation in action, consider the next examples.

If we persist an IntegerProperty as well as a StringProperty entity, and associate the StringProperty entity with a PropertyHolder, Hibernate will generate the following SQL queries:

Example 215. @Any mapping persist example
IntegerProperty ageProperty = new IntegerProperty();
ageProperty.setId(1L);
ageProperty.setName("age");
ageProperty.setValue(23);

session.persist(ageProperty);

StringProperty nameProperty = new StringProperty();
nameProperty.setId(1L);
nameProperty.setName("name");
nameProperty.setValue("John Doe");

session.persist(nameProperty);

PropertyHolder namePropertyHolder = new PropertyHolder();
namePropertyHolder.setId(1L);
namePropertyHolder.setProperty(nameProperty);

session.persist(namePropertyHolder);
INSERT INTO integer_property
       ( "name", "value", id )
VALUES ( 'age', 23, 1 )

INSERT INTO string_property
       ( "name", "value", id )
VALUES ( 'name', 'John Doe', 1 )

INSERT INTO property_holder
       ( property_type, property_id, id )
VALUES ( 'S', 1, 1 )

When fetching the PropertyHolder entity and navigating its property association, Hibernate will fetch the associated StringProperty entity like this:

Example 216. @Any mapping query example
PropertyHolder propertyHolder = session.get(PropertyHolder.class, 1L);

assertEquals("name", propertyHolder.getProperty().getName());
assertEquals("John Doe", propertyHolder.getProperty().getValue());
SELECT ph.id AS id1_1_0_,
       ph.property_type AS property2_1_0_,
       ph.property_id AS property3_1_0_
FROM   property_holder ph
WHERE  ph.id = 1


SELECT sp.id AS id1_2_0_,
       sp."name" AS name2_2_0_,
       sp."value" AS value3_2_0_
FROM   string_property sp
WHERE  sp.id = 1
Using meta-annotations

As mentioned in Mapping basic values, Hibernate’s ANY-related annotations can be composed using meta-annotations to re-use ANY mapping details.

Looking back at @Any mapping usage, we can see how cumbersome it would be to duplicate that information every time Property is mapped in the domain model. This description can also be moved into a single annotation that we can apply in each usage.

Example 217. @Any mapping usage
@Entity
@Table(name = "property_holder2")
public class PropertyHolder2 {

    @Id
    private Long id;

    @Any
    @PropertyDiscriminationDef
    @Column(name = "property_type")
    @JoinColumn(name = "property_id")
    private Property property;

    //Getters and setters are omitted for brevity

}

Though the mapping has been "simplified", the mapping works exactly as shown in @Any mapping usage.

@ManyToAny mapping

While the @Any mapping is useful to emulate a @ManyToOne association when there can be multiple target entities, to emulate a @OneToMany association, the @ManyToAny annotation must be used.

The mapping details are the same between @Any and @ManyToAny except for:

  1. The use of @ManyToAny instead of @Any

  2. The use of @JoinTable, @JoinTable#joinColumns and @JoinTable#inverseJoinColumns instead of just @JoinColumn

In the following example, the PropertyRepository entity has a collection of Property entities.

The repository_properties link table holds the associations between PropertyRepository and Property entities.

Example 218. @ManyToAny mapping usage
@Entity
@Table(name = "property_repository")
public class PropertyRepository {

    @Id
    private Long id;

    @ManyToAny
    @AnyDiscriminator(DiscriminatorType.STRING)
    @Column(name = "property_type")
    @AnyKeyJavaClass(Long.class)
    @AnyDiscriminatorValue(discriminator = "S", entity = StringProperty.class)
    @AnyDiscriminatorValue(discriminator = "I", entity = IntegerProperty.class)
    @Cascade(ALL)
    @JoinTable(name = "repository_properties",
            joinColumns = @JoinColumn(name = "repository_id"),
            inverseJoinColumns = @JoinColumn(name = "property_id")
   )
    private List<Property<?>> properties = new ArrayList<>();

    //Getters and setters are omitted for brevity

}
CREATE TABLE property_repository (
    id BIGINT NOT NULL,
    PRIMARY KEY ( id )
)

CREATE TABLE repository_properties (
    repository_id BIGINT NOT NULL,
    property_type VARCHAR(255),
    property_id BIGINT NOT NULL
)

To see the @ManyToAny annotation in action, consider the next examples.

If we persist an IntegerProperty as well as a StringProperty entity, and associate both of them with a PropertyRepository parent entity, Hibernate will generate the following SQL queries:

Example 219. @ManyToAny mapping persist example
IntegerProperty ageProperty = new IntegerProperty();
ageProperty.setId(1L);
ageProperty.setName("age");
ageProperty.setValue(23);

session.persist(ageProperty);

StringProperty nameProperty = new StringProperty();
nameProperty.setId(1L);
nameProperty.setName("name");
nameProperty.setValue("John Doe");

session.persist(nameProperty);

PropertyRepository propertyRepository = new PropertyRepository();
propertyRepository.setId(1L);

propertyRepository.getProperties().add(ageProperty);
propertyRepository.getProperties().add(nameProperty);

session.persist(propertyRepository);
INSERT INTO integer_property
       ( "name", "value", id )
VALUES ( 'age', 23, 1 )

INSERT INTO string_property
       ( "name", "value", id )
VALUES ( 'name', 'John Doe', 1 )

INSERT INTO property_repository ( id )
VALUES ( 1 )

INSERT INTO repository_properties
    ( repository_id , property_type , property_id )
VALUES
    ( 1 , 'I' , 1 )

When fetching the PropertyRepository entity and navigating its properties association, Hibernate will fetch the associated IntegerProperty and StringProperty entities like this:

Example 220. @ManyToAny mapping query example
PropertyRepository propertyRepository = session.get(PropertyRepository.class, 1L);

assertEquals(2, propertyRepository.getProperties().size());

for(Property property : propertyRepository.getProperties()) {
    assertNotNull(property.getValue());
}
SELECT pr.id AS id1_1_0_
FROM   property_repository pr
WHERE  pr.id = 1

SELECT ip.id AS id1_0_0_ ,
       ip."name" AS name2_0_0_ ,
       ip."value" AS value3_0_0_
FROM   integer_property ip
WHERE  ip.id = 1

SELECT sp.id AS id1_3_0_ ,
       sp."name" AS name2_3_0_ ,
       sp."value" AS value3_3_0_
FROM   string_property sp
WHERE  sp.id = 1

3.8.8. @JoinFormula mapping

The @JoinFormula annotation is used to customize the join between a child Foreign Key and a parent row Primary Key.

Example 221. @JoinFormula mapping usage
@Entity(name = "User")
@Table(name = "users")
public static class User {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	private String phoneNumber;

	@ManyToOne
	@JoinFormula("REGEXP_REPLACE(phoneNumber, '\\+(\\d+)-.*', '\\1')::int")
	private Country country;

	//Getters and setters omitted for brevity

}

@Entity(name = "Country")
@Table(name = "countries")
public static class Country {

	@Id
	private Integer id;

	private String name;

	//Getters and setters, equals and hashCode methods omitted for brevity

}
CREATE TABLE countries (
    id int4 NOT NULL,
    name VARCHAR(255),
    PRIMARY KEY ( id )
)

CREATE TABLE users (
    id int8 NOT NULL,
    firstName VARCHAR(255),
    lastName VARCHAR(255),
    phoneNumber VARCHAR(255),
    PRIMARY KEY ( id )
)

The country association in the User entity is mapped by the country identifier provided by the phoneNumber property.

Considering we have the following entities:

Example 222. @JoinFormula mapping usage
Country US = new Country();
US.setId(1);
US.setName("United States");

Country Romania = new Country();
Romania.setId(40);
Romania.setName("Romania");

doInJPA(this::entityManagerFactory, entityManager -> {
	entityManager.persist(US);
	entityManager.persist(Romania);
});

doInJPA(this::entityManagerFactory, entityManager -> {
	User user1 = new User();
	user1.setId(1L);
	user1.setFirstName("John");
	user1.setLastName("Doe");
	user1.setPhoneNumber("+1-234-5678");
	entityManager.persist(user1);

	User user2 = new User();
	user2.setId(2L);
	user2.setFirstName("Vlad");
	user2.setLastName("Mihalcea");
	user2.setPhoneNumber("+40-123-4567");
	entityManager.persist(user2);
});

When fetching the User entities, the country property is mapped by the @JoinFormula expression:

Example 223. @JoinFormula mapping usage
doInJPA(this::entityManagerFactory, entityManager -> {
	log.info("Fetch User entities");

	User john = entityManager.find(User.class, 1L);
	assertEquals(US, john.getCountry());

	User vlad = entityManager.find(User.class, 2L);
	assertEquals(Romania, vlad.getCountry());
});
-- Fetch User entities

SELECT
    u.id as id1_1_0_,
    u.firstName as firstNam2_1_0_,
    u.lastName as lastName3_1_0_,
    u.phoneNumber as phoneNum4_1_0_,
    REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int as formula1_0_,
    c.id as id1_0_1_,
    c.name as name2_0_1_
FROM
    users u
LEFT OUTER JOIN
    countries c
        ON REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int = c.id
WHERE
    u.id=?

-- binding parameter [1] as [BIGINT] - [1]

SELECT
    u.id as id1_1_0_,
    u.firstName as firstNam2_1_0_,
    u.lastName as lastName3_1_0_,
    u.phoneNumber as phoneNum4_1_0_,
    REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int as formula1_0_,
    c.id as id1_0_1_,
    c.name as name2_0_1_
FROM
    users u
LEFT OUTER JOIN
    countries c
        ON REGEXP_REPLACE(u.phoneNumber, '\+(\d+)-.*', '\1')::int = c.id
WHERE
    u.id=?

-- binding parameter [1] as [BIGINT] - [2]

Therefore, the @JoinFormula annotation is used to define a custom join association between the parent-child association.

3.8.9. @JoinColumnOrFormula mapping

The @JoinColumnOrFormula annotation is used to customize the join between a child Foreign Key and a parent row Primary Key when we need to take into consideration a column value as well as a @JoinFormula.

Example 224. @JoinColumnOrFormula mapping usage
@Entity(name = "User")
@Table(name = "users")
public static class User {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	private String language;

	@ManyToOne
	@JoinColumnOrFormula(column =
		@JoinColumn(
			name = "language",
			referencedColumnName = "primaryLanguage",
			insertable = false,
			updatable = false
		)
	)
	@JoinColumnOrFormula(formula =
		@JoinFormula(
			value = "true",
			referencedColumnName = "is_default"
		)
	)
	private Country country;

	//Getters and setters omitted for brevity

}

@Entity(name = "Country")
@Table(name = "countries")
public static class Country implements Serializable {

	@Id
	private Integer id;

	private String name;

	private String primaryLanguage;

	@Column(name = "is_default")
	private boolean _default;

	//Getters and setters, equals and hashCode methods omitted for brevity

}
CREATE TABLE countries (
    id INTEGER NOT NULL,
    is_default boolean,
    name VARCHAR(255),
    primaryLanguage VARCHAR(255),
    PRIMARY KEY ( id )
)

CREATE TABLE users (
    id BIGINT NOT NULL,
    firstName VARCHAR(255),
    language VARCHAR(255),
    lastName VARCHAR(255),
    PRIMARY KEY ( id )
)

The country association in the User entity is mapped by the language property value and the associated Country is_default column value.

Considering we have the following entities:

Example 225. @JoinColumnOrFormula persist example
Country US = new Country();
US.setId(1);
US.setDefault(true);
US.setPrimaryLanguage("English");
US.setName("United States");

Country Romania = new Country();
Romania.setId(40);
Romania.setDefault(true);
Romania.setName("Romania");
Romania.setPrimaryLanguage("Romanian");

doInJPA(this::entityManagerFactory, entityManager -> {
	entityManager.persist(US);
	entityManager.persist(Romania);
});

doInJPA(this::entityManagerFactory, entityManager -> {
	User user1 = new User();
	user1.setId(1L);
	user1.setFirstName("John");
	user1.setLastName("Doe");
	user1.setLanguage("English");
	entityManager.persist(user1);

	User user2 = new User();
	user2.setId(2L);
	user2.setFirstName("Vlad");
	user2.setLastName("Mihalcea");
	user2.setLanguage("Romanian");
	entityManager.persist(user2);

});

When fetching the User entities, the country property is mapped by the @JoinColumnOrFormula expression:

Example 226. @JoinColumnOrFormula fetching example
doInJPA(this::entityManagerFactory, entityManager -> {
	log.info("Fetch User entities");

	User john = entityManager.find(User.class, 1L);
	assertEquals(US, john.getCountry());

	User vlad = entityManager.find(User.class, 2L);
	assertEquals(Romania, vlad.getCountry());
});
SELECT
    u.id as id1_1_0_,
    u.language as language3_1_0_,
    u.firstName as firstNam2_1_0_,
    u.lastName as lastName4_1_0_,
    1 as formula1_0_,
    c.id as id1_0_1_,
    c.is_default as is_defau2_0_1_,
    c.name as name3_0_1_,
    c.primaryLanguage as primaryL4_0_1_
FROM
    users u
LEFT OUTER JOIN
    countries c
        ON u.language = c.primaryLanguage
        AND 1 = c.is_default
WHERE
    u.id = ?

-- binding parameter [1] as [BIGINT] - [1]

SELECT
    u.id as id1_1_0_,
    u.language as language3_1_0_,
    u.firstName as firstNam2_1_0_,
    u.lastName as lastName4_1_0_,
    1 as formula1_0_,
    c.id as id1_0_1_,
    c.is_default as is_defau2_0_1_,
    c.name as name3_0_1_,
    c.primaryLanguage as primaryL4_0_1_
FROM
    users u
LEFT OUTER JOIN
    countries c
        ON u.language = c.primaryLanguage
        AND 1 = c.is_default
WHERE
    u.id = ?

-- binding parameter [1] as [BIGINT] - [2]

Therefore, the @JoinColumnOrFormula annotation is used to define a custom join association between the parent-child association.

3.9. Collections

Hibernate supports mapping collections (java.util.Collection and java.util.Map subtypes) in a variety of ways.

Hibernate even allows mapping a collection as @Basic, but that should generally be avoided. See Collections as basic value type for details of such a mapping.

This section is limited to discussing @ElementCollection, @OneToMany and @ManyToMany.

Two entities cannot share a reference to the same collection instance.

Collection-valued properties do not support null value semantics.

Collections cannot be nested, meaning Hibernate does not support mapping List<List<?>>, for example.

Embeddables which are used as a collection element, Map value or Map key may not themselves define collections

3.9.1. Collection Semantics

The semantics of a collection describes how to handle the collection, including

  • the collection subtype to use - java.util.List, java.util.Set, java.util.SortedSet, etc.

  • how to access elements of the collection

  • how to create instances of the collection - both "raw" and "wrapper" forms.

Hibernate supports the following semantics:

ARRAY

Object and primitive arrays. See Mapping Arrays.

BAG

A collection that may contain duplicate entries and has no defined ordering. See Mapping Collections.

ID_BAG

A bag that defines a per-element identifier to uniquely identify elements in the collection. See Mapping Collections.

LIST

Follows the semantics defined by java.util.List. See Ordered Lists.

SET

Follows the semantics defined by java.util.Set. See Mapping Sets.

ORDERED_SET

A set that is ordered by a SQL fragment defined on its mapping. See Mapping Sets.

SORTED_SET

A set that is sorted according to a Comparator defined on its mapping. See Mapping Sets.

MAP

Follows the semantics defined by java.util.Map. See Mapping Maps.

ORDERED_MAP

A map that is ordered by keys according to a SQL fragment defined on its mapping. See Mapping Maps.

SORTED_MAP

A map that is sorted by keys according to a Comparator defined on its mapping. See Mapping Maps.

By default, Hibernate interprets the defined type of the plural attribute and makes an interpretation as to which classification it fits in to, using the following checks:

  1. if an array → ARRAY

  2. if a List → LIST

  3. if a SortedSet → SORTED_SET

  4. if a Set → SET

  5. if a SortedMap → SORTED_MAP

  6. if a Map → MAP

  7. else Collection → BAG

3.9.2. Mapping Lists

java.util.List defines a collection of ordered, non-unique elements.

Example 227. Basic List Mapping
@Entity
public class EntityWithList {
	// ...
	@ElementCollection
	private List<Name> names;
}

Contrary to natural expectations, the ordering of a list is by default not maintained. To maintain the order, it is necessary to explicitly use the jakarta.persistence.OrderColumn annotation.

Starting in 6.0, Hibernate allows to configure the default semantics of List without @OrderColumn via the hibernate.mapping.default_list_semantics setting. To switch to the more natural LIST semantics with an implicit order-column, set the setting to LIST. Beware that default LIST semantics only affects owned collection mappings. Unowned mappings like @ManyToMany(mappedBy = "…​") and @OneToMany(mappedBy = "…​") do not retain the element order by default, and explicitly annotating @OrderColumn for @ManyToMany(mappedBy = "…​") mappings is illegal.

To retain the order of elements of a @OneToMany(mappedBy = "…​") the @OrderColumn annotation must be applied explicitly. In addition to that, it is important that both sides of the relationship, the @OneToMany(mappedBy = "…​") and the @ManyToOne, must be kept in sync. Otherwise, the element position will not be updated accordingly.

The default column name that stores the index is derived from the attribute name, by suffixing _ORDER.

Example 228. @OrderColumn
@Entity
public class EntityWithOrderColumnList {
	// ...
	@ElementCollection
	@OrderColumn( name = "name_index" )
	private List<Name> names;
}

Now, a column named name_index will be used.

Hibernate stores index values into the order-column based on the element’s position in the list with no adjustment. The element at names[0] is stored with name_index=0 and so on. That is to say that the list index is considered 0-based just as list indexes themselves are 0-based. Some legacy schemas might map the position as 1-based, or any base really. Hibernate also defines support for such cases using its @ListIndexBase annotation.

Example 229. @ListIndexBase
@Entity
public class EntityWithIndexBasedList {
	// ...
	@ElementCollection
	@OrderColumn(name = "name_index")
	@ListIndexBase(1)
	private List<Name> names;
}

3.9.3. Mapping Sets

java.util.Set defines a collection of unique, though unordered elements. Hibernate supports mapping sets according to the requirements of the java.util.Set.

Example 230. Basic Set Mapping
@Entity
public class EntityWithSet {
	// ...
	@ElementCollection
	private Set<Name> names;
}

Hibernate also has the ability to map sorted and ordered sets. A sorted set orders its elements in memory via an associated Comparator; an ordered set is ordered via SQL when the set is loaded.

TIP

An ordered set does not perform any sorting in-memory. If an element is added after the collection is loaded, the collection would need to be refreshed to re-order the elements. For this reason, ordered sets are not recommended - if the application needs ordering of the set elements, a sorted set should be preferred. For this reason, it is not covered in the User Guide. See the javadocs for jakarta.persistence.OrderBy or org.hibernate.annotations.OrderBy for details.

There are 2 options for sorting a set - naturally or using an explicit comparator.

A set is naturally sorted using the natural sort comparator for its elements. Generally this implies that the element type is Comparable. E.g.

Example 231. @SortNatural
@Embeddable
@Access( AccessType.FIELD )
public class Name implements Comparable<Name> {
	private String first;
	private String last;

	// ...
}

@Entity
public class EntityWithNaturallySortedSet {
	// ...
	@ElementCollection
	@SortNatural
	private SortedSet<Name> names;
}

Because Name is defined as Comparable, its #compare method will be used to sort the elements in this set.

But Hibernate also allows sorting based on a specific Comparator implementation. Here, e.g., we map the Names as sorted by a NameComparator:

Example 232. @SortComparator
public class NameComparator implements Comparator<Name> {
	static final Comparator<Name> comparator = Comparator.comparing( Name::getLast ).thenComparing( Name::getFirst );

	@Override
	public int compare(Name o1, Name o2) {
		return comparator.compare( o1, o2 );
	}
}

@Entity
public class EntityWithSortedSet {
	// ...
	@ElementCollection
	@SortComparator( NameComparator.class )
	private SortedSet<Name> names;
}

Here, instead of Name#compare being use for the sorting, the explicit NameComparator will be used instead.

3.9.4. Mapping Maps

A java.util.Map is a collection of key/value pairs.

Example 233. Simple MAP mapping
@Entity
public class EntityWithMap {
	// ...
	@ElementCollection
	private Map<Name, Status> names;
}

Hibernate has the ability to map sorted and ordered maps - the ordering and sorting applies to the Map key. As we saw with Sets, the use of ordered Maps is generally discouraged.

Maps may be sorted naturally -

Example 234. Naturally sorted MAP mapping
@Entity
public class EntityWithNaturallySortedMap {
	// ...
	@ElementCollection
	@SortNatural
	private Map<Name, Status> names;
}

or via a Comparator -

Example 235. Comparator sorted MAP mapping
@Entity
public class EntityWithSortedMap {
	// ...
	@ElementCollection
	@SortComparator( NameComparator.class )
	private Map<Name, Status> names;
}

3.9.5. Mapping Collections

Without any other mapping influencers, java.util.Collection is interpreted using BAG semantics which means a collection that may contain duplicate entries and has no defined ordering.

Jakarta Persistence does not define support for BAG (nor ID_BAG) classification per-se. The specification does allow mapping of java.util.Collection attributes, but how such attributes are handled is largely undefined.

Example 236. Simple BAG mapping
@Entity
public class EntityWithBagAsCollection {
	// ..
	@ElementCollection
	private Collection<Name> names;
}

Some apps map BAG collections using java.util.List instead. Hibernate provides 2 ways to handle lists as bags. First an explicit annotation

Example 237. @Bag
@Entity
public class EntityWithBagAsList {
	// ..
	@ElementCollection
	@Bag
	private List<Name> names;
}

Specifically, the usage of @Bag forces the classification as BAG. Even though the names attribute is defined as List, Hibernate will treat it using the BAG semantics.

Additionally, as discussed in Mapping Lists, the hibernate.mapping.default_list_semantics setting is available to have Hibernate interpret a List with no @OrderColumn and no @ListIndexBase as a BAG.

An ID_BAG is similar to a BAG, except that it maps a generated, per-row identifier into the collection table. @CollectionId is the annotation to configure this identifier

3.9.6. Mapping Arrays

Hibernate is able to map Object and primitive arrays as collections. Mapping an array is essentially the same as mapping a list.

There is a major limitation of mapping arrays to be aware of - the array cannot be lazy using wrappers. It can, however, be lazy via bytecode enhancement of its owner.

Note that Jakarta Persistence does not define support for arrays as plural attributes; according to the specification, these would be mapped as binary data.

3.9.7. @ElementCollection

Element collections may contain values of either basic or embeddable types. They have a similar lifecycle to basic/embedded attributes in that their persistence is completely managed as part of the owner - they are created when referenced from an owner and automatically deleted when unreferenced. The specifics of how this lifecycle manifests in terms of database calls depends on the semantics of the mapping.

This section will discuss these lifecycle aspects using the example of mapping a collection of phone numbers. The examples use embeddable values, but the same aspects apply to collections of basic values as well.

The embeddable used in the examples is a PhoneNumber -

Example 238. PhoneNumber
@Embeddable
public class Phone {

	private String type;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}

First, a BAG mapping -

Example 239. Elemental BAG mapping
@Entity(name = "Person")
public static class Person {

	@Id
	private Integer id;

	@ElementCollection
	private Collection<String> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}
Example 240. Elemental BAG lifecycle
// Clear element collection and add element
person.getPhones().clear();
person.getPhones().add( "123-456-7890" );
person.getPhones().add( "456-000-1234" );
delete from Person_phones where Person_id=1

INSERT INTO Person_phones ( Person_id, phones )
VALUES ( 1, '123-456-7890' )

INSERT INTO Person_phones  (Person_id, phones)
VALUES  ( 1, '456-000-1234' )
Collections of entities

If value type collections can only form a one-to-many association between an owner entity and multiple basic or embeddable types, entity collections can represent both @OneToMany and @ManyToMany associations.

From a relational database perspective, associations are defined by the foreign key side (the child-side). With value type collections, only the entity can control the association (the parent-side), but for a collection of entities, both sides of the association are managed by the persistence context.

For this reason, entity collections can be devised into two main categories: unidirectional and bidirectional associations. Unidirectional associations are very similar to value type collections since only the parent side controls this relationship. Bidirectional associations are more tricky since, even if sides need to be in-sync at all times, only one side is responsible for managing the association. A bidirectional association has an owning side and an inverse (mappedBy) side.

3.9.8. @CollectionType

The @CollectionType annotation provides the ability to use a custom UserCollectionType implementation to influence how the collection for a plural attribute behaves.

As an example, consider a requirement for a collection with the semantics of a "unique list" - a cross between the ordered-ness of a List and the uniqueness of a Set. First the entity:

Example 241. @CollectionType
@Entity
public class TheEntityWithUniqueList {
	@ElementCollection
	@CollectionType(type = UniqueListType.class)
	private List<String> strings;

	// ...
}

The mapping says to use the UniqueListType class for the mapping of the plural attribute.

Example 242. UniqueListType
public class UniqueListType implements UserCollectionType {
	@Override
	public CollectionClassification getClassification() {
		return CollectionClassification.LIST;
	}

	@Override
	public Class<?> getCollectionClass() {
		return List.class;
	}

	@Override
	public PersistentCollection instantiate(
			SharedSessionContractImplementor session,
			CollectionPersister persister) {
		return new UniqueListWrapper( session );
	}

	@Override
	public PersistentCollection wrap(
			SharedSessionContractImplementor session,
			Object collection) {
		return new UniqueListWrapper( session, (List) collection );
	}

	@Override
	public Iterator getElementsIterator(Object collection) {
		return ( (List) collection ).iterator();
	}

	@Override
	public boolean contains(Object collection, Object entity) {
		return ( (List) collection ).contains( entity );
	}

	@Override
	public Object indexOf(Object collection, Object entity) {
		return ( (List) collection ).indexOf( entity );
	}

	@Override
	public Object replaceElements(
			Object original,
			Object target,
			CollectionPersister persister,
			Object owner,
			Map copyCache,
			SharedSessionContractImplementor session) {
		List result = (List) target;
		result.clear();
		result.addAll( (List) original );
		return result;
	}

	@Override
	public Object instantiate(int anticipatedSize) {
		return new ArrayList<>();
	}
}

Most custom UserCollectionType implementations will want their own PersistentCollection implementation.

Example 243. UniqueListWrapper
public class UniqueListWrapper<E> extends PersistentList<E> {
	public UniqueListWrapper(SharedSessionContractImplementor session) {
		super( session );
	}

	public UniqueListWrapper(SharedSessionContractImplementor session, List<E> list) {
		super( session, list );
	}

	// ...
}

UniqueListWrapper is the PersistentCollection implementation for the "unique list" semantic. See Wrappers for more details.

3.9.9. @CollectionTypeRegistration

For cases where an application wants to apply the same custom type to all plural attributes of a given classification, Hibernate also provides the @CollectionTypeRegistration:

Example 244. UniqueListType Registration
@Entity
@CollectionTypeRegistration( type = UniqueListType.class, classification = CollectionClassification.LIST )
public class TheEntityWithUniqueListRegistration {
	@ElementCollection
	private List<String> strings;

	// ...
}

This example behaves exactly as in @CollectionType.

3.9.10. Wrappers

As mentioned in Collection Semantics, Hibernate provides its own implementations of the Java collection types. These are called wrappers as they wrap an underlying collection and provide support for things like lazy loading, queueing add/remove operations while detached, etc. Hibernate defines the following PersistentCollection implementations for each of its collection classifications -

  • PersistentArrayHolder

  • PersistentBag

  • PersistentIdentifierBag

  • PersistentList

  • PersistentMap

  • PersistentSet

  • PersistentSortedMap

  • PersistentSortedSet

ORDERED_SET uses PersistentSet for its wrapper and ORDERED_MAP uses PersistentMap.

The collections they wrap are called "raw" collections, which are generally the standard Java implementations (java.util.ArrayList, etc)

Original content below

3.9.11. Bags

Bags are unordered lists, and we can have unidirectional bags or bidirectional ones.

Unidirectional bags

The unidirectional bag is mapped using a single @OneToMany annotation on the parent side of the association. Behind the scenes, Hibernate requires an association table to manage the parent-child relationship, as we can see in the following example:

Example 245. Unidirectional bag
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL)
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	private String type;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Person_Phone (
    Person_id BIGINT NOT NULL ,
    phones_id BIGINT NOT NULL
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    type VARCHAR(255) ,
    PRIMARY KEY ( id )
)

ALTER TABLE Person_Phone
ADD CONSTRAINT UK_9uhc5itwc9h5gcng944pcaslf
UNIQUE (phones_id)

ALTER TABLE Person_Phone
ADD CONSTRAINT FKr38us2n8g5p9rj0b494sd3391
FOREIGN KEY (phones_id) REFERENCES Phone

ALTER TABLE Person_Phone
ADD CONSTRAINT FK2ex4e4p7w1cj310kg2woisjl2
FOREIGN KEY (Person_id) REFERENCES Person

Because both the parent and the child sides are entities, the persistence context manages each entity separately.

The cascading mechanism allows you to propagate an entity state transition from a parent entity to its children.

By marking the parent side with the CascadeType.ALL attribute, the unidirectional association lifecycle becomes very similar to that of a value type collection.

Example 246. Unidirectional bag lifecycle
Person person = new Person(1L);
person.getPhones().add(new Phone(1L, "landline", "028-234-9876"));
person.getPhones().add(new Phone(2L, "mobile", "072-122-9876"));
entityManager.persist(person);
INSERT INTO Person ( id )
VALUES ( 1 )

INSERT INTO Phone ( number, type, id )
VALUES ( '028-234-9876', 'landline', 1 )

INSERT INTO Phone ( number, type, id )
VALUES ( '072-122-9876', 'mobile', 2 )

INSERT INTO Person_Phone ( Person_id, phones_id )
VALUES ( 1, 1 )

INSERT INTO Person_Phone ( Person_id, phones_id )
VALUES ( 1, 2 )

In the example above, once the parent entity is persisted, the child entities are going to be persisted as well.

Just like value type collections, unidirectional bags are not as efficient when it comes to modifying the collection structure (removing or reshuffling elements).

Because the parent-side cannot uniquely identify each individual child, Hibernate deletes all link table rows associated with the parent entity and re-adds the remaining ones that are found in the current collection state.

Bidirectional bags

The bidirectional bag is the most common type of entity collection. The @ManyToOne side is the owning side of the bidirectional bag association, while the @OneToMany is the inverse side, being marked with the mappedBy attribute.

Example 247. Bidirectional bag
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

	public void addPhone(Phone phone) {
		phones.add(phone);
		phone.setPerson(this);
	}

	public void removePhone(Phone phone) {
		phones.remove(phone);
		phone.setPerson(null);
	}
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	private String type;

	@Column(name = "`number`", unique = true)
	@NaturalId
	private String number;

	@ManyToOne
	private Person person;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}
CREATE TABLE Person (
    id BIGINT NOT NULL, PRIMARY KEY (id)
)

CREATE TABLE Phone (
    id BIGINT NOT NULL,
    number VARCHAR(255),
    type VARCHAR(255),
    person_id BIGINT,
    PRIMARY KEY (id)
)

ALTER TABLE Phone
ADD CONSTRAINT UK_l329ab0g4c1t78onljnxmbnp6
UNIQUE (number)

ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEy (person_id) REFERENCES Person
Example 248. Bidirectional bag lifecycle
person.addPhone(new Phone(1L, "landline", "028-234-9876"));
person.addPhone(new Phone(2L, "mobile", "072-122-9876"));
entityManager.flush();
person.removePhone(person.getPhones().get(0));
INSERT INTO Phone (number, person_id, type, id)
VALUES ( '028-234-9876', 1, 'landline', 1 )

INSERT INTO Phone (number, person_id, type, id)
VALUES ( '072-122-9876', 1, 'mobile', 2 )

UPDATE Phone
SET person_id = NULL, type = 'landline' where id = 1
Example 249. Bidirectional bag with orphan removal
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Phone> phones = new ArrayList<>();
DELETE FROM Phone WHERE id = 1

When rerunning the previous example, the child will get removed because the parent-side propagates the removal upon dissociating the child entity reference.

3.9.12. Ordered Lists

Although they use the List interface on the Java side, bags don’t retain element order. To preserve the collection element order, there are two possibilities:

@OrderBy

the collection is ordered upon retrieval using a child entity property

@OrderColumn

the collection uses a dedicated order column in the collection link table

Unidirectional ordered lists

When using the @OrderBy annotation, the mapping looks as follows:

Example 250. Unidirectional @OrderBy list
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL)
	@OrderBy("number")
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	private String type;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}

The database mapping is the same as with the Unidirectional bags example, so it won’t be repeated. Upon fetching the collection, Hibernate generates the following select statement:

Example 251. Unidirectional @OrderBy list select statement
SELECT
   phones0_.Person_id AS Person_i1_1_0_,
   phones0_.phones_id AS phones_i2_1_0_,
   unidirecti1_.id AS id1_2_1_,
   unidirecti1_."number" AS number2_2_1_,
   unidirecti1_.type AS type3_2_1_
FROM
   Person_Phone phones0_
INNER JOIN
   Phone unidirecti1_ ON phones0_.phones_id=unidirecti1_.id
WHERE
   phones0_.Person_id = 1
ORDER BY
   unidirecti1_."number"

The child table column is used to order the list elements.

The @OrderBy annotation can take multiple entity properties, and each property can take an ordering direction too (e.g. @OrderBy("name ASC, type DESC")).

If no property is specified (e.g. @OrderBy), the primary key of the child entity table is used for ordering.

Another ordering option is to use the @OrderColumn annotation:

Example 252. Unidirectional @OrderColumn list
@OneToMany(cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
private List<Phone> phones = new ArrayList<>();
CREATE TABLE Person_Phone (
    Person_id BIGINT NOT NULL ,
    phones_id BIGINT NOT NULL ,
    order_id INTEGER NOT NULL ,
    PRIMARY KEY ( Person_id, order_id )
)

This time, the link table takes the order_id column and uses it to materialize the collection element order. When fetching the list, the following select query is executed:

Example 253. Unidirectional @OrderColumn list select statement
select
   phones0_.Person_id as Person_i1_1_0_,
   phones0_.phones_id as phones_i2_1_0_,
   phones0_.order_id as order_id3_0_,
   unidirecti1_.id as id1_2_1_,
   unidirecti1_.number as number2_2_1_,
   unidirecti1_.type as type3_2_1_
from
   Person_Phone phones0_
inner join
   Phone unidirecti1_
      on phones0_.phones_id=unidirecti1_.id
where
   phones0_.Person_id = 1

With the order_id column in place, Hibernate can order the list in-memory after it’s being fetched from the database.

Bidirectional ordered lists

The mapping is similar with the Bidirectional bags example, just that the parent side is going to be annotated with either @OrderBy or @OrderColumn.

Example 254. Bidirectional @OrderBy list
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderBy("number")
private List<Phone> phones = new ArrayList<>();

Just like with the unidirectional @OrderBy list, the number column is used to order the statement on the SQL level.

When using the @OrderColumn annotation, the order_id column is going to be embedded in the child table:

Example 255. Bidirectional @OrderColumn list
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
private List<Phone> phones = new ArrayList<>();
CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    type VARCHAR(255) ,
    person_id BIGINT ,
    order_id INTEGER ,
    PRIMARY KEY ( id )
)

When fetching the collection, Hibernate will use the fetched ordered columns to sort the elements according to the @OrderColumn mapping.

Customizing ordered list ordinal

You can customize the ordinal of the underlying ordered list by using the @ListIndexBase annotation.

Example 256. @ListIndexBase mapping example
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@OrderColumn(name = "order_id")
@ListIndexBase(100)
private List<Phone> phones = new ArrayList<>();

When inserting two Phone records, Hibernate is going to start the List index from 100 this time.

Example 257. @ListIndexBase persist example
Person person = new Person(1L);
entityManager.persist(person);
person.addPhone(new Phone(1L, "landline", "028-234-9876"));
person.addPhone(new Phone(2L, "mobile", "072-122-9876"));
INSERT INTO Phone("number", person_id, type, id)
VALUES ('028-234-9876', 1, 'landline', 1)

INSERT INTO Phone("number", person_id, type, id)
VALUES ('072-122-9876', 1, 'mobile', 2)

UPDATE Phone
SET order_id = 100
WHERE id = 1

UPDATE Phone
SET order_id = 101
WHERE id = 2
Customizing ORDER BY SQL clause

While the Jakarta Persistence @OrderBy annotation allows you to specify the entity attributes used for sorting when fetching the current annotated collection, the Hibernate specific @OrderBy annotation is used to specify a SQL clause instead.

In the following example, the @OrderBy annotation uses the CHAR_LENGTH SQL function to order the Article entities by the number of characters of the name attribute.

Example 258. @OrderBy mapping example
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@OneToMany(
		mappedBy = "person",
		cascade = CascadeType.ALL
	)
	@SQLOrder("CHAR_LENGTH(name) DESC")
	private List<Article> articles = new ArrayList<>();

	//Getters and setters are omitted for brevity
}

@Entity(name = "Article")
public static class Article {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	private String content;

	@ManyToOne(fetch = FetchType.LAZY)
	private Person person;

	//Getters and setters are omitted for brevity
}

When fetching the articles collection, Hibernate uses the ORDER BY SQL clause provided by the mapping:

Example 259. @OrderBy fetching example
Person person = entityManager.find(Person.class, 1L);
assertEquals(
	"High-Performance Hibernate",
	person.getArticles().get(0).getName()
);
select
    a.person_id as person_i4_0_0_,
    a.id as id1_0_0_,
    a.content as content2_0_1_,
    a.name as name3_0_1_,
    a.person_id as person_i4_0_1_
from
    Article a
where
    a.person_id = ?
order by
    CHAR_LENGTH(a.name) desc

3.9.13. Sets

Sets are collections that don’t allow duplicate entries and Hibernate supports both the unordered Set and the natural-ordering SortedSet.

Unidirectional sets

The unidirectional set uses a link table to hold the parent-child associations and the entity mapping looks as follows:

Example 260. Unidirectional set
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL)
	private Set<Phone> phones = new HashSet<>();

	//Getters and setters are omitted for brevity
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	private String type;

	@NaturalId
	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}

The unidirectional set lifecycle is similar to that of the Unidirectional bags, so it can be omitted. The only difference is that Set doesn’t allow duplicates, but this constraint is enforced by the Java object contract rather than the database mapping.

When using Sets, it’s very important to supply proper equals/hashCode implementations for child entities.

In the absence of a custom equals/hashCode implementation logic, Hibernate will use the default Java reference-based object equality which might render unexpected results when mixing detached and managed object instances.

Bidirectional sets

Just like bidirectional bags, the bidirectional set doesn’t use a link table, and the child table has a foreign key referencing the parent table primary key. The lifecycle is just like with bidirectional bags except for the duplicates which are filtered out.

Example 261. Bidirectional set
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
	private Set<Phone> phones = new HashSet<>();

	//Getters and setters are omitted for brevity

	public void addPhone(Phone phone) {
		phones.add(phone);
		phone.setPerson(this);
	}

	public void removePhone(Phone phone) {
		phones.remove(phone);
		phone.setPerson(null);
	}
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	private String type;

	@Column(name = "`number`", unique = true)
	@NaturalId
	private String number;

	@ManyToOne
	private Person person;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}

3.9.14. Sorted sets

For sorted sets, the entity mapping must use the SortedSet interface instead. According to the SortedSet contract, all elements must implement the Comparable interface and therefore provide the sorting logic.

Unidirectional sorted sets

A SortedSet that relies on the natural sorting order given by the child element Comparable implementation logic might be annotated with the @SortNatural Hibernate annotation.

Example 262. Unidirectional natural sorted set
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL)
	@SortNatural
	private SortedSet<Phone> phones = new TreeSet<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Phone")
public static class Phone implements Comparable<Phone> {

	@Id
	private Long id;

	private String type;

	@NaturalId
	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

	@Override
	public int compareTo(Phone o) {
		return number.compareTo(o.getNumber());
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}

The lifecycle and the database mapping are identical to the Unidirectional bags, so they are intentionally omitted.

To provide a custom sorting logic, Hibernate also provides a @SortComparator annotation:

Example 263. Unidirectional custom comparator sorted set
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL)
	@SortComparator(ReverseComparator.class)
	private SortedSet<Phone> phones = new TreeSet<>();

	//Getters and setters are omitted for brevity

}

public static class ReverseComparator implements Comparator<Phone> {

	@Override
	public int compare(Phone o1, Phone o2) {
		return o2.compareTo(o1);
	}
}

@Entity(name = "Phone")
public static class Phone implements Comparable<Phone> {

	@Id
	private Long id;

	private String type;

	@NaturalId
	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

	@Override
	public int compareTo(Phone o) {
		return number.compareTo(o.getNumber());
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Phone phone = (Phone) o;
		return Objects.equals(number, phone.number);
	}

	@Override
	public int hashCode() {
		return Objects.hash(number);
	}
}
Bidirectional sorted sets

The @SortNatural and @SortComparator work the same for bidirectional sorted sets too:

Example 264. Bidirectional natural sorted set
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@SortNatural
private SortedSet<Phone> phones = new TreeSet<>();


//Getters and setters are omitted for brevity

Before v6, @SortNatural must be used if collection element’s natural ordering is relied upon for sorting. Starting from v6, we can omit @SortNatural as it will take effect by default.

3.9.15. Maps

A java.util.Map is a ternary association because it requires a parent entity, a map key, and a value. An entity can either be a map key or a map value, depending on the mapping. Hibernate allows using the following map keys:

MapKeyColumn

for value type maps, the map key is a column in the link table that defines the grouping logic

MapKey

the map key is either the primary key or another property of the entity stored as a map entry value

MapKeyEnumerated

the map key is an Enum of the target child entity

MapKeyTemporal

the map key is a Date or a Calendar of the target child entity

MapKeyJoinColumn

the map key is an entity mapped as an association in the child entity that’s stored as a map entry key

Value type maps

A map of value type must use the @ElementCollection annotation, just like value type lists, bags or sets.

Example 265. Value type map with an entity as a map key
public enum PhoneType {
	LAND_LINE,
	MOBILE
}

@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@Temporal(TemporalType.TIMESTAMP)
	@ElementCollection
	@CollectionTable(name = "phone_register")
	@Column(name = "since")
	private Map<Phone, Date> phoneRegister = new HashMap<>();

	//Getters and setters are omitted for brevity

}

@Embeddable
public static class Phone {

	private PhoneType type;

	@Column(name = "`number`")
	private String number;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE phone_register (
    Person_id BIGINT NOT NULL ,
    since TIMESTAMP ,
    number VARCHAR(255) NOT NULL ,
    type INTEGER NOT NULL ,
    PRIMARY KEY ( Person_id, number, type )
)

ALTER TABLE phone_register
ADD CONSTRAINT FKrmcsa34hr68of2rq8qf526mlk
FOREIGN KEY (Person_id) REFERENCES Person

Adding entries to the map generates the following SQL statements:

Example 266. Adding value type map entries
person.getPhoneRegister().put(
	new Phone(PhoneType.LAND_LINE, "028-234-9876"), new Date()
);
person.getPhoneRegister().put(
	new Phone(PhoneType.MOBILE, "072-122-9876"), new Date()
);
INSERT INTO phone_register (Person_id, number, type, since)
VALUES (1, '072-122-9876', 1, '2015-12-15 17:16:45.311')

INSERT INTO phone_register (Person_id, number, type, since)
VALUES (1, '028-234-9876', 0, '2015-12-15 17:16:45.311')
Maps with a custom key type

Hibernate defines the @MapKeyType annotation which you can use to customize the Map key type.

Considering you have the following tables in your database:

create table person (
    id int8 not null,
    primary key (id)
)

create table call_register (
    person_id int8 not null,
    phone_number int4,
    call_timestamp_epoch int8 not null,
    primary key (person_id, call_timestamp_epoch)
)

alter table if exists call_register
    add constraint FKsn58spsregnjyn8xt61qkxsub
    foreign key (person_id)
    references person

The call_register records the call history for every person. The call_timestamp_epoch column stores the phone call timestamp as a Unix timestamp since the Unix epoch.

The @MapKeyColumn annotation is used to define the table column holding the key while the @Column mapping gives the value of the java.util.Map in question.

Since we want to map all the calls by their associated java.util.Date, not by their timestamp since epoch which is a number, the entity mapping looks as follows:

Example 267. @MapKeyType mapping example
@Entity
@Table(name = "person")
public static class Person {

	@Id
	private Long id;

	@ElementCollection
	@CollectionTable(
		name = "call_register",
		joinColumns = @JoinColumn(name = "person_id")
	)
	@MapKeyJdbcTypeCode(Types.BIGINT)
	@MapKeyJavaType(JdbcTimestampJavaType.class)
	@MapKeyColumn(name = "call_timestamp_epoch")
	@Column(name = "phone_number")
	private Map<Date, Integer> callRegister = new HashMap<>();

	//Getters and setters are omitted for brevity

}
Maps having an interface type as the key

Considering you have the following PhoneNumber interface with an implementation given by the MobilePhone class type:

Example 268. PhoneNumber interface and the MobilePhone class type
public interface PhoneNumber {

	String get();
}

@Embeddable
public static class MobilePhone
		implements PhoneNumber {

	static PhoneNumber fromString(String phoneNumber) {
		String[] tokens = phoneNumber.split("-");
		if (tokens.length != 3) {
			throw new IllegalArgumentException("invalid phone number: " + phoneNumber);
		}
		int i = 0;
		return new MobilePhone(
			tokens[i++],
			tokens[i++],
			tokens[i]
		);
	}

	private MobilePhone() {
	}

	public MobilePhone(
			String countryCode,
			String operatorCode,
			String subscriberCode) {
		this.countryCode = countryCode;
		this.operatorCode = operatorCode;
		this.subscriberCode = subscriberCode;
	}

	@Column(name = "country_code")
	private String countryCode;

	@Column(name = "operator_code")
	private String operatorCode;

	@Column(name = "subscriber_code")
	private String subscriberCode;

	@Override
	public String get() {
		return String.format(
			"%s-%s-%s",
			countryCode,
			operatorCode,
			subscriberCode
		);
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		MobilePhone that = (MobilePhone) o;
		return Objects.equals(countryCode, that.countryCode) &&
				Objects.equals(operatorCode, that.operatorCode) &&
				Objects.equals(subscriberCode, that.subscriberCode);
	}

	@Override
	public int hashCode() {
		return Objects.hash(countryCode, operatorCode, subscriberCode);
	}
}

If you want to use the PhoneNumber interface as a java.util.Map key, then you need to supply the @MapKeyClass annotation as well.

Example 269. @MapKeyClass mapping example
@Entity
@Table(name = "person")
public static class Person {

	@Id
	private Long id;

	@ElementCollection
	@CollectionTable(
		name = "call_register",
		joinColumns = @JoinColumn(name = "person_id")
	)
	@MapKeyColumn(name = "call_timestamp_epoch")
	@MapKeyClass(MobilePhone.class)
	@Column(name = "call_register")
	private Map<PhoneNumber, Integer> callRegister = new HashMap<>();

	//Getters and setters are omitted for brevity
}
create table person (
    id bigint not null,
    primary key (id)
)

create table call_register (
    person_id bigint not null,
    call_register integer,
    country_code varchar(255) not null,
    operator_code varchar(255) not null,
    subscriber_code varchar(255) not null,
    primary key (person_id, country_code, operator_code, subscriber_code)
)

alter table call_register
    add constraint FKqyj2at6ik010jqckeaw23jtv2
    foreign key (person_id)
    references person

When inserting a Person with a callRegister containing 2 MobilePhone references, Hibernate generates the following SQL statements:

Example 270. @MapKeyClass persist example
Person person = new Person();
person.setId(1L);
person.getCallRegister().put(new MobilePhone("01", "234", "567"), 101);
person.getCallRegister().put(new MobilePhone("01", "234", "789"), 102);

entityManager.persist(person);
insert into person (id) values (?)

-- binding parameter [1] as [BIGINT] - [1]

insert into call_register(
    person_id,
    country_code,
    operator_code,
    subscriber_code,
    call_register
)
values
    (?, ?, ?, ?, ?)

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [VARCHAR] - [01]
-- binding parameter [3] as [VARCHAR] - [234]
-- binding parameter [4] as [VARCHAR] - [789]
-- binding parameter [5] as [INTEGER] - [102]

insert into call_register(
    person_id,
    country_code,
    operator_code,
    subscriber_code,
    call_register
)
values
    (?, ?, ?, ?, ?)

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [VARCHAR] - [01]
-- binding parameter [3] as [VARCHAR] - [234]
-- binding parameter [4] as [VARCHAR] - [567]
-- binding parameter [5] as [INTEGER] - [101]

When fetching a Person and accessing the callRegister Map, Hibernate generates the following SQL statements:

Example 271. @MapKeyClass fetch example
Person person = entityManager.find(Person.class, 1L);
assertEquals(2, person.getCallRegister().size());

assertEquals(
	Integer.valueOf(101),
	person.getCallRegister().get(MobilePhone.fromString("01-234-567"))
);

assertEquals(
	Integer.valueOf(102),
	person.getCallRegister().get(MobilePhone.fromString("01-234-789"))
);
select
    cr.person_id as person_i1_0_0_,
    cr.call_register as call_reg2_0_0_,
    cr.country_code as country_3_0_,
    cr.operator_code as operator4_0_,
    cr.subscriber_code as subscrib5_0_
from
    call_register cr
where
    cr.person_id = ?

-- binding parameter [1] as [BIGINT] - [1]

-- extracted value ([person_i1_0_0_] : [BIGINT])  - [1]
-- extracted value ([call_reg2_0_0_] : [INTEGER]) - [101]
-- extracted value ([country_3_0_]   : [VARCHAR]) - [01]
-- extracted value ([operator4_0_]   : [VARCHAR]) - [234]
-- extracted value ([subscrib5_0_]   : [VARCHAR]) - [567]

-- extracted value ([person_i1_0_0_] : [BIGINT])  - [1]
-- extracted value ([call_reg2_0_0_] : [INTEGER]) - [102]
-- extracted value ([country_3_0_]   : [VARCHAR]) - [01]
-- extracted value ([operator4_0_]   : [VARCHAR]) - [234]
-- extracted value ([subscrib5_0_]   : [VARCHAR]) - [789]
Unidirectional maps

A unidirectional map exposes a parent-child association from the parent-side only.

The following example shows a unidirectional map which also uses a @MapKeyTemporal annotation. The map key is a timestamp, and it’s taken from the child entity table.

The @MapKey annotation is used to define the entity attribute used as a key of the java.util.Map in question.

Example 272. Unidirectional Map
public enum PhoneType {
	LAND_LINE,
	MOBILE
}

@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
	@JoinTable(
		name = "phone_register",
		joinColumns = @JoinColumn(name = "phone_id"),
		inverseJoinColumns = @JoinColumn(name = "person_id"))
	@MapKey(name = "since")
	@MapKeyTemporal(TemporalType.TIMESTAMP)
	private Map<Date, Phone> phoneRegister = new HashMap<>();

	//Getters and setters are omitted for brevity

	public void addPhone(Phone phone) {
		phoneRegister.put(phone.getSince(), phone);
	}
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	private PhoneType type;

	@Column(name = "`number`")
	private String number;

	private Date since;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    since TIMESTAMP ,
    type INTEGER ,
    PRIMARY KEY ( id )
)

CREATE TABLE phone_register (
    phone_id BIGINT NOT NULL ,
    person_id BIGINT NOT NULL ,
    PRIMARY KEY ( phone_id, person_id )
)

ALTER TABLE phone_register
ADD CONSTRAINT FKc3jajlx41lw6clbygbw8wm65w
FOREIGN KEY (person_id) REFERENCES Phone

ALTER TABLE phone_register
ADD CONSTRAINT FK6npoomh1rp660o1b55py9ndw4
FOREIGN KEY (phone_id) REFERENCES Person
Bidirectional maps

Like most bidirectional associations, this relationship is owned by the child-side while the parent is the inverse side and can propagate its own state transitions to the child entities.

In the following example, you can see that @MapKeyEnumerated was used so that the Phone enumeration becomes the map key.

Example 273. Bidirectional Map
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	@OneToMany(mappedBy = "person", cascade = CascadeType.ALL, orphanRemoval = true)
	@MapKey(name = "type")
	@MapKeyEnumerated
	private Map<PhoneType, Phone> phoneRegister = new HashMap<>();

	//Getters and setters are omitted for brevity

	public void addPhone(Phone phone) {
		phone.setPerson(this);
		phoneRegister.put(phone.getType(), phone);
	}
}

@Entity(name = "Phone")
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	private PhoneType type;

	@Column(name = "`number`")
	private String number;

	private Date since;

	@ManyToOne
	private Person person;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE Phone (
    id BIGINT NOT NULL ,
    number VARCHAR(255) ,
    since TIMESTAMP ,
    type INTEGER ,
    person_id BIGINT ,
    PRIMARY KEY ( id )
)

ALTER TABLE Phone
ADD CONSTRAINT FKmw13yfsjypiiq0i1osdkaeqpg
FOREIGN KEY (person_id) REFERENCES Person

3.9.16. Arrays

When discussing arrays, it is important to understand the distinction between SQL array types and Java arrays that are mapped as part of the application’s domain model.

Not all databases implement the SQL-99 ARRAY type and, for this reason, the SQL type used by Hibernate for arrays varies depending on the database support.

It is impossible for Hibernate to offer lazy-loading for arrays of entities and, for this reason, it is strongly recommended to map a "collection" of entities using a List or Set rather than an array.

3.9.17. Arrays as basic value type

By default, Hibernate will choose a type for the array based on Dialect.getPreferredSqlTypeCodeForArray(). Prior to Hibernate 6.1, the default was to always use the BINARY type, as supported by the current Dialect, but now, Hibernate will leverage the native array data types if possible.

To force the BINARY type, the persistent attribute has to be annotated with @JdbcTypeCode(SqlTypes.VARBINARY).

Example 274. Arrays stored as SQL array
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String[] phones;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL,
    phones VARCHAR(255) ARRAY,
    PRIMARY KEY ( id )
)

3.9.18. Collections as basic value type

Notice how all the previous examples explicitly mark the collection attribute as either @ElementCollection, @OneToMany or @ManyToMany.

Attributes of collection or array type without any of those annotations are considered basic types and by default mapped like basic arrays as depicted in the previous section.

Example 275. Collections stored as SQL array
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private List<String> phones;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Person (
    id BIGINT NOT NULL,
    phones VARCHAR(255) ARRAY,
    PRIMARY KEY ( id )
)

Prior to Hibernate 6.1, it was common to use an AttributeConverter to map the elements into e.g. a comma separated list which is still a viable option. Just note that it is not required anymore.

Example 276. Comma delimited collection
public class CommaDelimitedStringsConverter implements AttributeConverter<List<String>,String> {
	@Override
	public String convertToDatabaseColumn(List<String> attributeValue) {
		if ( attributeValue == null ) {
			return null;
		}
		return join( ",", attributeValue );
	}

	@Override
	public List<String> convertToEntityAttribute(String dbData) {
		if ( dbData == null ) {
			return null;
		}
		return listOf( dbData.split( "," ) );
	}
}

@Entity( name = "Person" )
public static class Person {
    @Id
    private Integer id;
    @Basic
	private String name;
	@Basic
	@Convert( converter = CommaDelimitedStringsConverter.class )
	private List<String> nickNames;

	// ...

}

3.10. Natural Ids

Natural ids represent domain model unique identifiers that have a meaning in the real world too. Even if a natural id does not make a good primary key (surrogate keys being usually preferred), it’s still useful to tell Hibernate about it. As we will see later, Hibernate provides a dedicated, efficient API for loading an entity by its natural id much like it offers for loading by identifier (PK).

All values used in a natural id must be non-nullable.

For natural id mappings using a to-one association, this precludes the use of not-found mappings which effectively define a nullable mapping.

3.10.1. Natural Id Mapping

Natural ids are defined in terms of one or more persistent attributes.

Example 277. Natural id using single basic attribute
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	@NaturalId
	private String isbn;

	//Getters and setters are omitted for brevity
}
Example 278. Natural id using single embedded attribute
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	@NaturalId
	@Embedded
	private Isbn isbn;

	//Getters and setters are omitted for brevity
}

@Embeddable
public static class Isbn implements Serializable {

	private String isbn10;

	private String isbn13;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Isbn isbn = (Isbn) o;
		return Objects.equals(isbn10, isbn.isbn10) &&
				Objects.equals(isbn13, isbn.isbn13);
	}

	@Override
	public int hashCode() {
		return Objects.hash(isbn10, isbn13);
	}
}
Example 279. Natural id using multiple persistent attributes
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	@NaturalId
	private String productNumber;

	@NaturalId
	@ManyToOne(fetch = FetchType.LAZY)
	private Publisher publisher;

	//Getters and setters are omitted for brevity
}

@Entity(name = "Publisher")
public static class Publisher implements Serializable {

	@Id
	private Long id;

	private String name;

	//Getters and setters are omitted for brevity

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (o == null || getClass() != o.getClass()) {
			return false;
		}
		Publisher publisher = (Publisher) o;
		return Objects.equals(id, publisher.id) &&
				Objects.equals(name, publisher.name);
	}

	@Override
	public int hashCode() {
		return Objects.hash(id, name);
	}
}

3.10.2. Natural Id API

As stated before, Hibernate provides an API for loading entities by their associated natural id. This is represented by the org.hibernate.NaturalIdLoadAccess contract obtained via Session#byNaturalId.

If the entity does not define a natural id, trying to load an entity by its natural id will throw an exception.

Example 280. Using NaturalIdLoadAccess
Book book = entityManager
	.unwrap(Session.class)
	.byNaturalId(Book.class)
	.using("isbn", "978-9730228236")
	.load();
Book book = entityManager
	.unwrap(Session.class)
	.byNaturalId(Book.class)
	.using(
		"isbn",
		new Isbn(
			"973022823X",
			"978-9730228236"
		))
	.load();
Book book = entityManager
	.unwrap(Session.class)
	.byNaturalId(Book.class)
	.using("productNumber", "973022823X")
	.using("publisher", publisher)
	.load();

NaturalIdLoadAccess offers 2 distinct methods for obtaining the entity:

load()

obtains a reference to the entity, making sure that the entity state is initialized.

getReference()

obtains a reference to the entity. The state may or may not be initialized. If the entity is already associated with the current running Session, that reference (loaded or not) is returned. If the entity is not loaded in the current Session and the entity supports proxy generation, an uninitialized proxy is generated and returned, otherwise the entity is loaded from the database and returned.

NaturalIdLoadAccess allows loading an entity by natural id and at the same time applies a pessimistic lock. For additional details on locking, see the Locking chapter.

We will discuss the last method available on NaturalIdLoadAccess ( setSynchronizationEnabled() ) in Natural Id - Mutability and Caching.

Because the Book entities in the first two examples define "simple" natural ids, we can load them as follows:

Example 281. Loading by simple natural id
Book book = entityManager
	.unwrap(Session.class)
	.bySimpleNaturalId(Book.class)
	.load("978-9730228236");
Book book = entityManager
	.unwrap(Session.class)
	.bySimpleNaturalId(Book.class)
	.load(
		new Isbn(
			"973022823X",
			"978-9730228236"
		)
	);

Here we see the use of the org.hibernate.SimpleNaturalIdLoadAccess contract, obtained via Session#bySimpleNaturalId().

SimpleNaturalIdLoadAccess is similar to NaturalIdLoadAccess except that it does not define the using method. Instead, because these simple natural ids are defined based on just one attribute we can directly pass the corresponding natural id attribute value directly to the load() and getReference() methods.

If the entity does not define a natural id, or if the natural id is not of a "simple" type, an exception will be thrown there.

3.10.3. Natural Id - Mutability and Caching

A natural id may be mutable or immutable. By default the @NaturalId annotation marks an immutable natural id attribute. An immutable natural id is expected to never change its value.

If the value(s) of the natural id attribute(s) change, @NaturalId(mutable = true) should be used instead.

Example 282. Mutable natural id mapping
@Entity(name = "Author")
public static class Author {

	@Id
	private Long id;

	private String name;

	@NaturalId(mutable = true)
	private String email;

	//Getters and setters are omitted for brevity
}

Within the Session, Hibernate maintains a mapping from natural id values to entity identifiers (PK) values. If natural ids values changed, it is possible for this mapping to become out of date until a flush occurs.

To work around this condition, Hibernate will attempt to discover any such pending changes and adjust them when the load() or getReference() methods are executed. To be clear: this is only pertinent for mutable natural ids.

This discovery and adjustment have a performance impact. If you are certain that none of the mutable natural ids already associated with the current Session have changed, you can disable this checking by calling setSynchronizationEnabled(false) (the default is true). This will force Hibernate to circumvent the checking of mutable natural ids.

Example 283. Mutable natural id synchronization use-case
Author author = entityManager
	.unwrap(Session.class)
	.bySimpleNaturalId(Author.class)
	.load("john@acme.com");

author.setEmail("john.doe@acme.com");

assertNull(
	entityManager
		.unwrap(Session.class)
		.bySimpleNaturalId(Author.class)
		.setSynchronizationEnabled(false)
		.load("john.doe@acme.com")
);

assertSame(author,
	entityManager
		.unwrap(Session.class)
		.bySimpleNaturalId(Author.class)
		.setSynchronizationEnabled(true)
		.load("john.doe@acme.com")
);

Not only can this NaturalId-to-PK resolution be cached in the Session, but we can also have it cached in the second-level cache if second level caching is enabled.

Example 284. Natural id caching
@Entity(name = "Book")
@NaturalIdCache
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	@NaturalId
	private String isbn;

	//Getters and setters are omitted for brevity
}

3.11. Partitioning

In data management, it is sometimes necessary to split data of a table into various (physical) partitions, based on partition keys and a partitioning scheme.

Due to the nature of partitioning, it is vital for the database to know the partition key of a row for certain operations, like SQL update and delete statements. If a database doesn’t know the partition of a row that should be updated or deleted, then it must look for the row in all partitions, leading to poor performance.

The @PartitionKey annotation is a way to tell Hibernate about the column, such that it can include a column restriction as predicate into SQL update and delete statements for entity state changes.

3.11.1. Partition Key Mapping

Partition keys are defined in terms of one or more persistent attributes.

Example 285. Partition key using single basic attribute
@Entity(name = "User")
public static class User {

	@Id
	private Long id;

	private String firstname;

	private String lastname;

	@PartitionKey
	private String tenantKey;

	//Getters and setters are omitted for brevity
}

When updating or deleting an entity, Hibernate will include a partition key constraint similar to this

update user_tbl set firstname=?,lastname=?,tenantKey=? where id=? and tenantKey=?
delete from user_tbl where id=? and tenantKey=?

3.12. Soft Delete

An occasional requirement seen in the wild is to never physically remove rows from the database, but to instead perform a "soft delete" where a column is updated to indicate that the row is no longer active. Hibernate offers first-class support for this behavior through its @SoftDelete annotation.

The @SoftDelete annotation is new in 6.4.

It was possible to hack together support for soft deletes in previous versions using a combination of filters, @Where and custom delete event handling. However, that approach was tedious and did not work in all cases. @SoftDelete should be highly preferred.

Hibernate supports soft delete for both entities and collections.

Soft delete support is defined by 3 main parts -

  1. A strategy for interpreting the stored indicator values.

  2. The column which contains the indicator.

  3. A conversion from Boolean indicator value to the proper database type

3.12.1. Strategy - SoftDeleteType

Given truth values, there are 2 valid ways to interpret the values stored in the database. This interpretation is defined by the SoftDeleteType enumeration and can be configured per-usage using @SoftDelete(…​, strategy=ACTIVE) or @SoftDelete(…​, strategy=DELETED) -

ACTIVE

Tracks rows which are active. A true value in the database indicates that the row is active (non-deleted); a false value indicates inactive (deleted).

DELETED

Tracks rows which are deleted. A true value in the database indicates that the row is deleted; a false value indicates that the row is non-deleted.

3.12.2. Indicator column

The column where the indicator value is stored is defined using @SoftDelete#columnName attribute.

The default column name depends on the strategy being used -

ACTIVE

The default column name is active.

DELETED

The default column name is deleted.

See Basic entity soft-delete for an example of customizing the column name.

Depending on the conversion type, an appropriate check constraint may be applied to the column.

3.12.3. Indicator conversion

The conversion is defined using a Jakarta Persistence AttributeConverter. The domain-type is always boolean. The relational-type can be any type, as defined by the converter; generally BOOLEAN, BIT, INTEGER or CHAR.

An explicit conversion can be specified using @SoftDelete#converter. See Basic entity soft-delete for an example of specifying an explicit conversion. Explicit conversions can specify a custom converter or leverage Hibernate-provided converters for the 3 most common cases -

NumericBooleanConverter

Defines conversion using 0 for false and 1 for true

YesNoConverter

Defines conversion using 'N' for false and 'Y' for true

TrueFalseConverter

Defines conversion using 'F' for false and 'T' for true

If an explicit converter is not specified, Hibernate will follow the same resolution steps defined in Boolean to determine the proper database type -

boolean (and bit)

the underlying type is boolean / bit and no conversion is applied

numeric

the underlying type is integer and values are converted according to NumericBooleanConverter

character

the underlying type is char and values are converted according to TrueFalseConverter

The converter should simply convert the true and false, irrespective of the strategy used. Hibernate will handle applying the strategy.

3.12.4. Entity soft delete

Hibernate supports the soft delete of entities, with the indicator column defined on the primary table.

Example 286. Basic entity soft-delete
@Entity(name = "SimpleEntity")
@SoftDelete(columnName = "removed", converter = YesNoConverter.class)
public class SimpleEntity {
	// ...
}

For entity hierarchies, the soft delete applies to all inheritance types.

Example 287. Inherited entity soft-delete
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@SoftDelete(columnName = "removed", converter = YesNoConverter.class)
public abstract class JoinedRoot {
	// ...
}
@Entity
@Table(name = "joined_sub")
@PrimaryKeyJoinColumn(name = "joined_fk")
public class JoinedSub extends JoinedRoot {
	// ...
}

3.12.5. Collection soft delete

Soft delete may be applied to collection mapped with a "collection table", aka @ElementCollection and @ManyToMany. The soft delete applies to the collection table row.

Annotating a @OneToMany association with @SoftDelete will throw an exception.

In the case of @OneToMany and @ManyToMany, the mapped entity may itself be soft deletable which is handled transparently.

Example 288. Soft delete for @ElementCollection
@ElementCollection
@CollectionTable(name = "elements", joinColumns = @JoinColumn(name = "owner_fk"))
@Column(name = "txt")
@SoftDelete(converter = YesNoConverter.class)
private Collection<String> elements;

Given this @ElementCollection mapping, rows in the elements table will be soft deleted using an indicator column named deleted.

Example 289. Soft delete for @ManyToMany
@ManyToMany
@JoinTable(
		name = "m2m",
		joinColumns = @JoinColumn(name = "owner_fk"),
		inverseJoinColumns = @JoinColumn(name = "owned_fk")
)
@SoftDelete(columnName = "gone", converter = NumericBooleanConverter.class)
private Collection<CollectionOwned> manyToMany;

Given this @ManyToMany mapping, rows in the m2m table will be soft deleted using an indicator column named gone.

3.12.6. Package-level soft delete

The @SoftDelete annotation may also be placed at the package level, in which case it applies to all entities and collections defined within the package.

3.13. Dynamic Model

Jakarta Persistence only acknowledges the POJO entity model mapping so, if you are concerned about Jakarta Persistence provider portability, it’s best to stick to the strict POJO model. On the other hand, Hibernate can work with both POJO entities and dynamic entity models.

3.13.1. Dynamic mapping models

Persistent entities do not necessarily have to be represented as POJO/JavaBean classes. Hibernate also supports dynamic models (using Map of Maps at runtime). With this approach, you do not write persistent classes, only mapping files.

A given entity has just one entity mode within a given SessionFactory. This is a change from previous versions which allowed to define multiple entity modes for an entity and to select which to load. Entity modes can now be mixed within a domain model; a dynamic entity might reference a POJO entity and vice versa.

Example 290. Dynamic domain model Hibernate mapping
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class entity-name="Book">
        <id name="isbn" column="isbn" length="32" type="string"/>

        <property name="title" not-null="true" length="50" type="string"/>

        <property name="author" not-null="true" length="50" type="string"/>

    </class>
</hibernate-mapping>

After you defined your entity mapping, you need to instruct Hibernate to use the dynamic mapping mode:

Example 291. Dynamic domain model Hibernate mapping
settings.put("hibernate.default_entity_mode", "dynamic-map");

When you are going to save the following Book dynamic entity, Hibernate is going to generate the following SQL statement:

Example 292. Persist dynamic entity
Map<String, String> book = new HashMap<>();
book.put("isbn", "978-9730228236");
book.put("title", "High-Performance Java Persistence");
book.put("author", "Vlad Mihalcea");

entityManager
	.unwrap(Session.class)
	.persist("Book", book);
insert
into
    Book
    (title, author, isbn)
values
    (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [2] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [3] as [VARCHAR] - [978-9730228236]

The main advantage of dynamic models is the quick turnaround time for prototyping without the need for entity class implementation. The main downfall is that you lose compile-time type checking and will likely deal with many exceptions at runtime. However, as a result of the Hibernate mapping, the database schema can easily be normalized and sound, allowing to add a proper domain model implementation on top later on.

It is also interesting to note that dynamic models are great for certain integration use cases as well. Envers, for example, makes extensive use of dynamic models to represent the historical data.

3.14. Inheritance

Although relational database systems don’t provide support for inheritance, Hibernate provides several strategies to leverage this object-oriented trait onto domain model entities:

MappedSuperclass

Inheritance is implemented in the domain model only without reflecting it in the database schema. See MappedSuperclass.

Single table

The domain model class hierarchy is materialized into a single table which contains entities belonging to different class types. See Single table.

Joined table

The base class and all the subclasses have their own database tables and fetching a subclass entity requires a join with the parent table as well. See Joined table.

Table per class

Each subclass has its own table containing both the subclass and the base class properties. See Table per class.

3.14.1. MappedSuperclass

In the following domain model class hierarchy, a DebitAccount and a CreditAccount share the same Account base class.

Inheritance class diagram

When using MappedSuperclass, the inheritance is visible in the domain model only, and each database table contains both the base class and the subclass properties.

Example 293. @MappedSuperclass inheritance
@MappedSuperclass
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE DebitAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    overdraftFee NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

CREATE TABLE CreditAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    creditLimit NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

Because the @MappedSuperclass inheritance model is not mirrored at the database level, it’s not possible to use polymorphic queries referencing the @MappedSuperclass when fetching persistent objects by their base class.

3.14.2. Single table

The single table inheritance strategy maps all subclasses to only one database table. Each subclass declares its own persistent properties. Version and id properties are assumed to be inherited from the root class.

When omitting an explicit inheritance strategy (e.g. @Inheritance), Jakarta Persistence will choose the SINGLE_TABLE strategy by default.

Example 294. Single Table inheritance
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Account (
    DTYPE VARCHAR(31) NOT NULL ,
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    overdraftFee NUMERIC(19, 2) ,
    creditLimit NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

Each subclass in a hierarchy must define a unique discriminator value, which is used to differentiate between rows belonging to separate subclass types. If this is not specified, the DTYPE column is used as a discriminator, storing the associated subclass name.

Example 295. Single Table inheritance discriminator column
DebitAccount debitAccount = new DebitAccount();
debitAccount.setId(1L);
debitAccount.setOwner("John Doe");
debitAccount.setBalance(BigDecimal.valueOf(100));
debitAccount.setInterestRate(BigDecimal.valueOf(1.5d));
debitAccount.setOverdraftFee(BigDecimal.valueOf(25));

CreditAccount creditAccount = new CreditAccount();
creditAccount.setId(2L);
creditAccount.setOwner("John Doe");
creditAccount.setBalance(BigDecimal.valueOf(1000));
creditAccount.setInterestRate(BigDecimal.valueOf(1.9d));
creditAccount.setCreditLimit(BigDecimal.valueOf(5000));

entityManager.persist(debitAccount);
entityManager.persist(creditAccount);
INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (100, 1.5, 'John Doe', 25, 'DebitAccount', 1)

INSERT INTO Account (balance, interestRate, owner, creditLimit, DTYPE, id)
VALUES (1000, 1.9, 'John Doe', 5000, 'CreditAccount', 2)

When using polymorphic queries, only a single table is required to be scanned to fetch all associated subclass instances.

Example 296. Single Table polymorphic query
List<Account> accounts = entityManager
	.createQuery("select a from Account a")
	.getResultList();
SELECT  singletabl0_.id AS id2_0_ ,
        singletabl0_.balance AS balance3_0_ ,
        singletabl0_.interestRate AS interest4_0_ ,
        singletabl0_.owner AS owner5_0_ ,
        singletabl0_.overdraftFee AS overdraf6_0_ ,
        singletabl0_.creditLimit AS creditLi7_0_ ,
        singletabl0_.DTYPE AS DTYPE1_0_
FROM    Account singletabl0_

Among all other inheritance alternatives, the single table strategy performs the best since it requires access to one table only. Because all subclass columns are stored in a single table, it’s not possible to use NOT NULL constraints anymore, so integrity checks must be moved either into the data access layer or enforced through CHECK or TRIGGER constraints.

Discriminator

The discriminator column contains marker values that tell the persistence layer what subclass to instantiate for a particular row. Hibernate Core supports the following restricted set of types as discriminator column: String, char, int, byte, short, boolean(including yes_no, true_false).

Use the @DiscriminatorColumn to define the discriminator column as well as the discriminator type.

The enum DiscriminatorType used in jakarta.persistence.DiscriminatorColumn only contains the values STRING, CHAR and INTEGER which means that not all Hibernate supported types are available via the @DiscriminatorColumn annotation. You can also use @DiscriminatorFormula to express in SQL a virtual discriminator column. This is particularly useful when the discriminator value can be extracted from one or more columns of the table. Both @DiscriminatorColumn and @DiscriminatorFormula are to be set on the root entity (once per persisted hierarchy).

@org.hibernate.annotations.DiscriminatorOptions allows to optionally specify Hibernate-specific discriminator options which are not standardized in Jakarta Persistence. The available options are force and insert.

The force attribute is useful if the table contains rows with extra discriminator values that are not mapped to a persistent class. This could, for example, occur when working with a legacy database. If force is set to true, Hibernate will specify the allowed discriminator values in the SELECT query even when retrieving all instances of the root class.

The second option, insert, tells Hibernate whether or not to include the discriminator column in SQL INSERTs. Usually, the column should be part of the INSERT statement, but if your discriminator column is also part of a mapped composite identifier you have to set this option to false.

There used to be a @org.hibernate.annotations.ForceDiscriminator annotation which was deprecated in version 3.6 and later removed. Use @DiscriminatorOptions instead.

Discriminator formula

Assuming a legacy database schema where the discriminator is based on inspecting a certain column, we can take advantage of the Hibernate specific @DiscriminatorFormula annotation and map the inheritance model as follows:

Example 297. Single Table discriminator formula
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorFormula(
	"case when debitKey is not null " +
	"then 'Debit' " +
	"else (" +
	"   case when creditKey is not null " +
	"   then 'Credit' " +
	"   else 'Unknown' " +
	"   end) " +
	"end "
)
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
@DiscriminatorValue(value = "Debit")
public static class DebitAccount extends Account {

	private String debitKey;

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
@DiscriminatorValue(value = "Credit")
public static class CreditAccount extends Account {

	private String creditKey;

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Account (
    id int8 NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    debitKey VARCHAR(255) ,
    overdraftFee NUMERIC(19, 2) ,
    creditKey VARCHAR(255) ,
    creditLimit NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

The @DiscriminatorFormula defines a custom SQL clause that can be used to identify a certain subclass type. The @DiscriminatorValue defines the mapping between the result of the @DiscriminatorFormula and the inheritance subclass type.

Implicit discriminator values

Aside from the usual discriminator values assigned to each individual subclass type, the @DiscriminatorValue can take two additional values:

null

If the underlying discriminator column is null, the null discriminator mapping is going to be used.

not null

If the underlying discriminator column has a not-null value that is not explicitly mapped to any entity, the not-null discriminator mapping used.

To understand how these two values work, consider the following entity mapping:

Example 298. @DiscriminatorValue null and not-null entity mapping
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorValue("null")
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
@DiscriminatorValue("Debit")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
@DiscriminatorValue("Credit")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}

@Entity(name = "OtherAccount")
@DiscriminatorValue("not null")
public static class OtherAccount extends Account {

	private boolean active;

	//Getters and setters are omitted for brevity

}

The Account class has a @DiscriminatorValue( "null" ) mapping, meaning that any account row which does not contain any discriminator value will be mapped to an Account base class entity. The DebitAccount and CreditAccount entities use explicit discriminator values. The OtherAccount entity is used as a generic account type because it maps any database row whose discriminator column is not explicitly assigned to any other entity in the current inheritance tree.

To visualize how it works, consider the following example:

Example 299. @DiscriminatorValue null and not-null entity persistence
DebitAccount debitAccount = new DebitAccount();
debitAccount.setId(1L);
debitAccount.setOwner("John Doe");
debitAccount.setBalance(BigDecimal.valueOf(100));
debitAccount.setInterestRate(BigDecimal.valueOf(1.5d));
debitAccount.setOverdraftFee(BigDecimal.valueOf(25));

CreditAccount creditAccount = new CreditAccount();
creditAccount.setId(2L);
creditAccount.setOwner("John Doe");
creditAccount.setBalance(BigDecimal.valueOf(1000));
creditAccount.setInterestRate(BigDecimal.valueOf(1.9d));
creditAccount.setCreditLimit(BigDecimal.valueOf(5000));

Account account = new Account();
account.setId(3L);
account.setOwner("John Doe");
account.setBalance(BigDecimal.valueOf(1000));
account.setInterestRate(BigDecimal.valueOf(1.9d));

entityManager.persist(debitAccount);
entityManager.persist(creditAccount);
entityManager.persist(account);

entityManager.unwrap(Session.class).doWork(connection -> {
	try(Statement statement = connection.createStatement()) {
		statement.executeUpdate(
			"insert into Account (DTYPE, active, balance, interestRate, owner, id) " +
			"values ('Other', true, 25, 0.5, 'Vlad', 4)"
		);
	}
});

Map<Long, Account> accounts = entityManager.createQuery(
	"select a from Account a", Account.class)
.getResultList()
.stream()
.collect(Collectors.toMap(Account::getId, Function.identity()));

assertEquals(4, accounts.size());
assertEquals(DebitAccount.class, accounts.get(1L).getClass());
assertEquals(CreditAccount.class, accounts.get(2L).getClass());
assertEquals(Account.class, accounts.get(3L).getClass());
assertEquals(OtherAccount.class, accounts.get(4L).getClass());
INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (100, 1.5, 'John Doe', 25, 'Debit', 1)

INSERT INTO Account (balance, interestRate, owner, overdraftFee, DTYPE, id)
VALUES (1000, 1.9, 'John Doe', 5000, 'Credit', 2)

INSERT INTO Account (balance, interestRate, owner, id)
VALUES (1000, 1.9, 'John Doe', 3)

INSERT INTO Account (DTYPE, active, balance, interestRate, owner, id)
VALUES ('Other', true, 25, 0.5, 'Vlad', 4)

SELECT a.id as id2_0_,
       a.balance as balance3_0_,
       a.interestRate as interest4_0_,
       a.owner as owner5_0_,
       a.overdraftFee as overdraf6_0_,
       a.creditLimit as creditLi7_0_,
       a.active as active8_0_,
       a.DTYPE as DTYPE1_0_
FROM   Account a

As you can see, the Account entity row has a value of NULL in the DTYPE discriminator column, while the OtherAccount entity was saved with a DTYPE column value of other which has not explicit mapping.

3.14.3. Joined table

Each subclass can also be mapped to its own table. This is also called table-per-subclass mapping strategy. An inherited state is retrieved by joining with the table of the superclass.

A discriminator column is not required for this mapping strategy. Each subclass must, however, declare a table column holding the object identifier.

Example 300. Join Table
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Account (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE CreditAccount (
    creditLimit NUMERIC(19, 2) ,
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

CREATE TABLE DebitAccount (
    overdraftFee NUMERIC(19, 2) ,
    id BIGINT NOT NULL ,
    PRIMARY KEY ( id )
)

ALTER TABLE CreditAccount
ADD CONSTRAINT FKihw8h3j1k0w31cnyu7jcl7n7n
FOREIGN KEY (id) REFERENCES Account

ALTER TABLE DebitAccount
ADD CONSTRAINT FKia914478noepymc468kiaivqm
FOREIGN KEY (id) REFERENCES Account

The primary keys of the CreditAccount and DebitAccount tables are also foreign keys to the superclass table primary key and described by the @PrimaryKeyJoinColumns.

The table name still defaults to the non-qualified class name. Also, if @PrimaryKeyJoinColumn is not set, the primary key / foreign key columns are assumed to have the same names as the primary key columns of the primary table of the superclass.

Example 301. Join Table with @PrimaryKeyJoinColumn
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
@PrimaryKeyJoinColumn(name = "account_id")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
@PrimaryKeyJoinColumn(name = "account_id")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE CreditAccount (
    creditLimit NUMERIC(19, 2) ,
    account_id BIGINT NOT NULL ,
    PRIMARY KEY ( account_id )
)

CREATE TABLE DebitAccount (
    overdraftFee NUMERIC(19, 2) ,
    account_id BIGINT NOT NULL ,
    PRIMARY KEY ( account_id )
)

ALTER TABLE CreditAccount
ADD CONSTRAINT FK8ulmk1wgs5x7igo370jt0q005
FOREIGN KEY (account_id) REFERENCES Account

ALTER TABLE DebitAccount
ADD CONSTRAINT FK7wjufa570onoidv4omkkru06j
FOREIGN KEY (account_id) REFERENCES Account

When using polymorphic queries, the base class table must be joined with all subclass tables to fetch every associated subclass instance.

Example 302. Join Table polymorphic query
List<Account> accounts = entityManager
	.createQuery("select a from Account a")
	.getResultList();
SELECT jointablet0_.id AS id1_0_ ,
       jointablet0_.balance AS balance2_0_ ,
       jointablet0_.interestRate AS interest3_0_ ,
       jointablet0_.owner AS owner4_0_ ,
       jointablet0_1_.overdraftFee AS overdraf1_2_ ,
       jointablet0_2_.creditLimit AS creditLi1_1_ ,
       CASE WHEN jointablet0_1_.id IS NOT NULL THEN 1
            WHEN jointablet0_2_.id IS NOT NULL THEN 2
            WHEN jointablet0_.id IS NOT NULL THEN 0
       END AS clazz_
FROM   Account jointablet0_
       LEFT OUTER JOIN DebitAccount jointablet0_1_ ON jointablet0_.id = jointablet0_1_.id
       LEFT OUTER JOIN CreditAccount jointablet0_2_ ON jointablet0_.id = jointablet0_2_.id

The joined table inheritance polymorphic queries can use several JOINS which might affect performance when fetching a large number of entities.

3.14.4. Table per class

A third option is to map only the concrete classes of an inheritance hierarchy to tables. This is called the table-per-concrete-class strategy. Each table defines all persistent states of the class, including the inherited state.

In Hibernate, it is not necessary to explicitly map such inheritance hierarchies. You can map each class as a separate entity root. However, if you wish to use polymorphic associations (e.g. an association to the superclass of your hierarchy), you need to use the union subclass mapping.

Example 303. Table per class
@Entity(name = "Account")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public static class Account {

	@Id
	private Long id;

	private String owner;

	private BigDecimal balance;

	private BigDecimal interestRate;

	//Getters and setters are omitted for brevity

}

@Entity(name = "DebitAccount")
public static class DebitAccount extends Account {

	private BigDecimal overdraftFee;

	//Getters and setters are omitted for brevity

}

@Entity(name = "CreditAccount")
public static class CreditAccount extends Account {

	private BigDecimal creditLimit;

	//Getters and setters are omitted for brevity

}
CREATE TABLE Account (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    PRIMARY KEY ( id )
)

CREATE TABLE CreditAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    creditLimit NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

CREATE TABLE DebitAccount (
    id BIGINT NOT NULL ,
    balance NUMERIC(19, 2) ,
    interestRate NUMERIC(19, 2) ,
    owner VARCHAR(255) ,
    overdraftFee NUMERIC(19, 2) ,
    PRIMARY KEY ( id )
)

When using polymorphic queries, a UNION is required to fetch the base class table along with all subclass tables as well.

Example 304. Table per class polymorphic query
List<Account> accounts = entityManager
	.createQuery("select a from Account a")
	.getResultList();
SELECT tablepercl0_.id AS id1_0_ ,
       tablepercl0_.balance AS balance2_0_ ,
       tablepercl0_.interestRate AS interest3_0_ ,
       tablepercl0_.owner AS owner4_0_ ,
       tablepercl0_.overdraftFee AS overdraf1_2_ ,
       tablepercl0_.creditLimit AS creditLi1_1_ ,
       tablepercl0_.clazz_ AS clazz_
FROM (
    SELECT    id ,
             balance ,
             interestRate ,
             owner ,
             CAST(NULL AS INT) AS overdraftFee ,
             CAST(NULL AS INT) AS creditLimit ,
             0 AS clazz_
    FROM     Account
    UNION ALL
    SELECT   id ,
             balance ,
             interestRate ,
             owner ,
             overdraftFee ,
             CAST(NULL AS INT) AS creditLimit ,
             1 AS clazz_
    FROM     DebitAccount
    UNION ALL
    SELECT   id ,
             balance ,
             interestRate ,
             owner ,
             CAST(NULL AS INT) AS overdraftFee ,
             creditLimit ,
             2 AS clazz_
    FROM     CreditAccount
) tablepercl0_

Polymorphic queries require multiple UNION queries, so be aware of the performance implications of a large class hierarchy.

3.14.5. Implicit and explicit polymorphism

By default, when you query a base class entity, the polymorphic query will fetch all subclasses belonging to the base type.

However, you can even query interfaces or base classes that don’t belong to the Jakarta Persistence entity inheritance model.

For instance, considering the following DomainModelEntity interface:

Example 305. DomainModelEntity interface
public interface DomainModelEntity<ID> {

    ID getId();

    Integer getVersion();
}

If we have two entity mappings, a Book and a Blog, and the Blog entity is mapped with the @Polymorphism annotation and taking the PolymorphismType.EXPLICIT setting:

Example 306. @Polymorphism entity mapping
@Entity(name = "Event")
public static class Book implements DomainModelEntity<Long> {

	@Id
	private Long id;

	@Version
	private Integer version;

	private String title;

	private String author;

	//Getter and setters omitted for brevity
}

@Entity(name = "Blog")
@Polymorphism(type = PolymorphismType.EXPLICIT)
public static class Blog implements DomainModelEntity<Long> {

	@Id
	private Long id;

	@Version
	private Integer version;

	private String site;

	//Getter and setters omitted for brevity
}

If we have the following entity objects in our system:

Example 307. Domain Model entity objects
Book book = new Book();
book.setId(1L);
book.setAuthor("Vlad Mihalcea");
book.setTitle("High-Performance Java Persistence");
entityManager.persist(book);

Blog blog = new Blog();
blog.setId(1L);
blog.setSite("vladmihalcea.com");
entityManager.persist(blog);

We can now query against the DomainModelEntity interface, and Hibernate is going to fetch only the entities that are either mapped with @Polymorphism(type = PolymorphismType.IMPLICIT) or they are not annotated at all with the @Polymorphism annotation (implying the IMPLICIT behavior):

Example 308. Fetching Domain Model entities using non-mapped base class polymorphism
List<DomainModelEntity> accounts = entityManager
.createQuery(
	"select e " +
	"from org.hibernate.orm.test.inheritance.polymorphism.DomainModelEntity e")
.getResultList();

assertEquals(1, accounts.size());
assertTrue(accounts.get(0) instanceof Book);

Therefore, only the Book was fetched since the Blog entity was marked with the @Polymorphism(type = PolymorphismType.EXPLICIT) annotation, which instructs Hibernate to skip it when executing a polymorphic query against a non-mapped base class.

3.15. Mutability

Immutability can be specified for both entities and attributes.

Unfortunately mutability is an overloaded term. It can refer to either:

  • Whether the internal state of a value can be changed. In this sense, a java.lang.Date is considered mutable because its internal state can be changed by calling Date#setTime, whereas java.lang.String is considered immutable because its internal state cannot be changed. Hibernate uses this distinction for numerous internal optimizations related to dirty checking and making copies.

  • Whether the value is updateable in regard to the database. Hibernate can perform other optimizations based on this distinction.

3.15.1. @Immutable

The @Immutable annotation declares something immutable in the updateability sense. Mutable (updateable) is the implicit condition.

@Immutable is allowed on an entity, attribute, AttributeConverter and UserType. Unfortunately, it has slightly different impacts depending on where it is placed; see the linked sections for details.

3.15.2. Entity immutability

If a specific entity is immutable, it is good practice to mark it with the @Immutable annotation.

Example 309. Immutable entity
@Entity(name = "Event")
@Immutable
public static class Event {

	@Id
	private Long id;

	private Date createdOn;

	private String message;

	//Getters and setters are omitted for brevity

}

Internally, Hibernate is going to perform several optimizations, such as:

  • reducing memory footprint since there is no need to retain the loaded state for the dirty checking mechanism

  • speeding-up the Persistence Context flushing phase since immutable entities can skip the dirty checking process

Considering the following entity is persisted in the database:

Example 310. Persisting an immutable entity
Event event = new Event();
event.setId(1L);
event.setCreatedOn(new Date());
event.setMessage("Hibernate User Guide rocks!");

entityManager.persist(event);

When loading the entity and trying to change its state, Hibernate will skip any modification, therefore no SQL UPDATE statement is executed.

Example 311. The immutable entity ignores any update
Event event = entityManager.find(Event.class, 1L);
log.info("Change event message");
event.setMessage("Hibernate User Guide");
SELECT e.id AS id1_0_0_,
       e.createdOn AS createdO2_0_0_,
       e.message AS message3_0_0_
FROM   event e
WHERE  e.id = 1

-- Change event message

SELECT e.id AS id1_0_0_,
       e.createdOn AS createdO2_0_0_,
       e.message AS message3_0_0_
FROM   event e
WHERE  e.id = 1

@Mutability is not allowed on an entity.

3.15.3. Attribute mutability

The @Immutable annotation may also be used on attributes. The impact varies slightly depending on the exact kind of attribute.

@Mutability on an attribute applies the specified MutabilityPlan to the attribute for handling internal state changes in the values for the attribute.

Attribute immutability - basic

When applied to a basic attribute, @Immutable implies immutability in both the updateable and internal-state sense. E.g.

Example 312. Immutable basic attribute
@Immutable
private Date theDate;

Changes to the theDate attribute are ignored.

Example 313. Immutable basic attribute change
final TheEntity theEntity = session.find( TheEntity.class, 1 );
// this change will be ignored
theEntity.theDate.setTime( Instant.EPOCH.toEpochMilli() );
Attribute immutability - embeddable

To be continued..

Attribute immutability - plural

Plural attributes (@ElementCollection, @OneToMany`, @ManyToMany and @ManyToAny) may also be annotated with @Immutable.

TIP

While most immutable changes are simply discarded, modifying an immutable collection will cause an exception.

Example 314. Persisting an immutable collection
Batch batch = new Batch();
batch.setId(1L);
batch.setName("Change request");

Event event1 = new Event();
event1.setId(1L);
event1.setCreatedOn(new Date());
event1.setMessage("Update Hibernate User Guide");

Event event2 = new Event();
event2.setId(2L);
event2.setCreatedOn(new Date());
event2.setMessage("Update Hibernate Getting Started Guide");

batch.getEvents().add(event1);
batch.getEvents().add(event2);

entityManager.persist(batch);

The Batch entity is mutable. Only the events collection is immutable.

For instance, we can still modify the entity name:

Example 315. Changing the mutable entity
Batch batch = entityManager.find(Batch.class, 1L);
log.info("Change batch name");
batch.setName("Proposed change request");
SELECT b.id AS id1_0_0_,
       b.name AS name2_0_0_
FROM   Batch b
WHERE  b.id = 1

-- Change batch name

UPDATE batch
SET    name = 'Proposed change request'
WHERE  id = 1

However, when trying to modify the events collection:

Example 316. Immutable collections cannot be modified
try {
		Batch batch = entityManager.find( Batch.class, 1L );
		batch.getEvents().clear();
}
catch (Exception e) {
	log.error("Immutable collections cannot be modified");
}
jakarta.persistence.RollbackException: Error while committing the transaction

Caused by: jakarta.persistence.PersistenceException: org.hibernate.HibernateException:

Caused by: org.hibernate.HibernateException: changed an immutable collection instance: [
    org.hibernate.orm.test.mapping.mutability.attribute.PluralAttributeMutabilityTest$Batch.events#1
]
Attribute immutability - entity

To be continued..

3.15.4. AttributeConverter mutability

Declaring @Mutability on an AttributeConverter applies the specified MutabilityPlan to all value mappings (attribute, collection element, etc.) to which the converter is applied.

Declaring @Immutable on an AttributeConverter is shorthand for declaring @Mutability with an immutable MutabilityPlan.

3.15.5. UserType mutability

Similar to AttributeConverter both @Mutability and @Immutable may be declared on a UserType.

@Mutability applies the specified MutabilityPlan to all value mappings (attribute, collection element, etc.) to which the UserType is applied.

@Immutable applies an immutable MutabilityPlan to all value mappings (attribute, collection element, etc.) to which the UserType is applied.

3.15.6. @Mutability

MutabilityPlan is the contract used by Hibernate to abstract mutability concerns, in the sense of internal state changes.

A Java type has an inherent MutabilityPlan based on its JavaType#getMutabilityPlan.

The @Mutability annotation allows a specific MutabilityPlan to be used and is allowed on an attribute, AttributeConverter and UserType. When used on a AttributeConverter or UserType, the specified MutabilityPlan is effective for all basic values to which the AttributeConverter or UserType is applied.

To understand the impact of internal-state mutability, consider the following entity:

Example 317. Basic mutability model
@Entity
public class MutabilityBaselineEntity {
	@Id
	private Integer id;
	@Basic
	private String name;
	@Basic
	private Date activeTimestamp;
}

When dealing with an inherently immutable value, such as a String, there is only one way to update the value:

Example 318. Changing immutable value
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.setName( "new name" );

During flush, this change will make the entity "dirty" and the changes will be written (UPDATE) to the database.

When dealing with mutable values, however, Hibernate must be aware of both ways to change the value. First, like with the immutable value, we can set the new value:

Example 319. Changing mutable value - setting
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.setActiveTimestamp( now() );

We can also mutate the existing value:

Example 320. Changing mutable value - mutating
Session session = getSession();
MutabilityBaselineEntity entity = session.find( MutabilityBaselineEntity.class, 1 );
entity.getActiveTimestamp().setTime( now().getTime() );

This mutating example has the same effect as the setting example - they each will make the entity dirty.

3.16. Customizing the domain model

For cases where Hibernate does not provide a built-in way to configure the domain model mapping based on requirements, it provides a very broad and flexible way to adjust the mapping model through its "boot-time model" (defined in the org.hibernate.mapping package) using its @AttributeBinderType meta annotation and corresponding AttributeBinder contract.

An example:

Example 321. AttributeBinder example
/**
 * Custom annotation applying 'Y'/'N' storage semantics to a boolean.
 *
 * The important piece here is `@AttributeBinderType`
 */
@Target({METHOD,FIELD})
@Retention(RUNTIME)
@AttributeBinderType( binder = YesNoBinder.class )
public @interface YesNo {
}

/**
 * The actual binder responsible for configuring the model objects
 */
public class YesNoBinder implements AttributeBinder<YesNo> {
	@Override
	public void bind(
			YesNo annotation,
			MetadataBuildingContext buildingContext,
			PersistentClass persistentClass,
			Property property) {
		( (SimpleValue) property.getValue() ).setJpaAttributeConverterDescriptor(
				new InstanceBasedConverterDescriptor(
						YesNoConverter.INSTANCE,
						buildingContext.getBootstrapContext().getClassmateContext()
				)
		);
	}
}

The important thing to take away here is that both @YesNo and YesNoBinder are custom, user-written code. Hibernate has no inherent understanding of what a @YesNo does or is. It only understands that it has the @AttributeBinderType meta-annotation and knows how to apply that through the corresponding YesNoBinder.

Notice also that @AttributeBinderType provides a type-safe way to perform configuration because the AttributeBinder (YesNoBinder) is handed the custom annotation (@YesNo) to grab its configured attributes. @YesNo does not provide any attributes, but it easily could. Whatever YesNoBinder supports.

4. Bootstrap

The term bootstrapping refers to initializing and starting a software component. In Hibernate, we are specifically talking about the process of building a fully functional SessionFactory instance or EntityManagerFactory instance, for Jakarta Persistence. The process is very different for each.

During the bootstrap process, you might want to customize Hibernate behavior so make sure you check the Configuration Settings section as well.

4.1. Native Bootstrapping

This section discusses the process of bootstrapping a Hibernate SessionFactory. Specifically, it addresses the bootstrapping APIs. For a discussion of the legacy bootstrapping API, see Legacy Bootstrapping.

4.1.1. Building the ServiceRegistry

The first step in native bootstrapping is the building of a ServiceRegistry holding the services Hibernate will need during bootstrapping and at run time.

Actually, we are concerned with building 2 different ServiceRegistries. First is the org.hibernate.boot.registry.BootstrapServiceRegistry. The BootstrapServiceRegistry is intended to hold services that Hibernate needs at both bootstrap and run time. This boils down to 3 services:

org.hibernate.boot.registry.classloading.spi.ClassLoaderService

which controls how Hibernate interacts with ClassLoaders.

org.hibernate.integrator.spi.IntegratorService

which controls the management and discovery of org.hibernate.integrator.spi.Integrator instances.

org.hibernate.boot.registry.selector.spi.StrategySelector

which controls how Hibernate resolves implementations of various strategy contracts. This is a very powerful service, but a full discussion of it is beyond the scope of this guide.

If you are ok with the default behavior of Hibernate in regards to these BootstrapServiceRegistry services (which is quite often the case, especially in stand-alone environments), then you don’t need to explicitly build the BootstrapServiceRegistry.

If you wish to alter how the BootstrapServiceRegistry is built, that is controlled through the org.hibernate.boot.registry.BootstrapServiceRegistryBuilder:

Example 322. Controlling BootstrapServiceRegistry building
BootstrapServiceRegistryBuilder bootstrapRegistryBuilder =
    new BootstrapServiceRegistryBuilder();
// add a custom ClassLoader
bootstrapRegistryBuilder.applyClassLoader(customClassLoader);
// manually add an Integrator
bootstrapRegistryBuilder.applyIntegrator(customIntegrator);

BootstrapServiceRegistry bootstrapRegistry = bootstrapRegistryBuilder.build();

The services of the BootstrapServiceRegistry cannot be extended (added to) nor overridden (replaced).

The second ServiceRegistry is the org.hibernate.boot.registry.StandardServiceRegistry. You will almost always need to configure the StandardServiceRegistry, which is done through org.hibernate.boot.registry.StandardServiceRegistryBuilder:

Example 323. Building a BootstrapServiceRegistryBuilder
// An example using an implicitly built BootstrapServiceRegistry
StandardServiceRegistryBuilder standardRegistryBuilder =
    new StandardServiceRegistryBuilder();

// An example using an explicitly built BootstrapServiceRegistry
BootstrapServiceRegistry bootstrapRegistry =
    new BootstrapServiceRegistryBuilder().build();

StandardServiceRegistryBuilder standardRegistryBuilder =
    new StandardServiceRegistryBuilder(bootstrapRegistry);

A StandardServiceRegistry is also highly configurable via the StandardServiceRegistryBuilder API. See the StandardServiceRegistryBuilder Javadocs for more details.

Some specific methods of interest:

Example 324. Configuring a MetadataSources
ServiceRegistry standardRegistry =
        new StandardServiceRegistryBuilder().build();

MetadataSources sources = new MetadataSources(standardRegistry);

// alternatively, we can build the MetadataSources without passing
// a service registry, in which case it will build a default
// BootstrapServiceRegistry to use.  But the approach shown
// above is preferred
// MetadataSources sources = new MetadataSources();

// add a class using JPA/Hibernate annotations for mapping
sources.addAnnotatedClass(MyEntity.class);

// add the name of a class using JPA/Hibernate annotations for mapping.
// differs from above in that accessing the Class is deferred which is
// important if using runtime bytecode-enhancement
sources.addAnnotatedClassName("org.hibernate.example.Customer");

// Read package-level metadata.
sources.addPackage("hibernate.example");

// Read package-level metadata.
sources.addPackage(MyEntity.class.getPackage());

// Adds the named hbm.xml resource as a source: which performs the
// classpath lookup and parses the XML
sources.addResource("org/hibernate/example/Order.hbm.xml");

// Adds the named JPA orm.xml resource as a source: which performs the
// classpath lookup and parses the XML
sources.addResource("org/hibernate/example/Product.orm.xml");

// Read all mapping documents from a directory tree.
// Assumes that any file named *.hbm.xml is a mapping document.
sources.addDirectory(new File("."));

// Read mappings from a particular XML file
sources.addFile(new File("./mapping.xml"));

// Read all mappings from a jar file.
// Assumes that any file named *.hbm.xml is a mapping document.
sources.addJar(new File("./entities.jar"));

4.1.2. Event Listener registration

The main use cases for an org.hibernate.integrator.spi.Integrator right now are registering event listeners.

Example 325. Configuring an event listener
public class MyIntegrator implements Integrator {

    @Override
    public void integrate(
            Metadata metadata,
            BootstrapContext bootstrapContext,
            SessionFactoryImplementor sessionFactory) {

        // As you might expect, an EventListenerRegistry is the thing with which event
        // listeners are registered
        // It is a service so we look it up using the service registry
        final EventListenerRegistry eventListenerRegistry =
            bootstrapContext.getServiceRegistry().getService(EventListenerRegistry.class);

        // If you wish to have custom determination and handling of "duplicate" listeners,
        // you would have to add an implementation of the
        // org.hibernate.event.service.spi.DuplicationStrategy contract like this
        eventListenerRegistry.addDuplicationStrategy(new CustomDuplicationStrategy());

        // EventListenerRegistry defines 3 ways to register listeners:

        // 1) This form overrides any existing registrations with
        eventListenerRegistry.setListeners(EventType.AUTO_FLUSH,
                                            DefaultAutoFlushEventListener.class);

        // 2) This form adds the specified listener(s) to the beginning of the listener chain
        eventListenerRegistry.prependListeners(EventType.PERSIST,
                                                DefaultPersistEventListener.class);

        // 3) This form adds the specified listener(s) to the end of the listener chain
        eventListenerRegistry.appendListeners(EventType.MERGE,
                                               DefaultMergeEventListener.class);
    }

    @Override
    public void disintegrate(
            SessionFactoryImplementor sessionFactory,
            SessionFactoryServiceRegistry serviceRegistry) {

    }
}

4.1.3. Building the Metadata

The second step in native bootstrapping is the building of an org.hibernate.boot.Metadata object containing the parsed representations of an application domain model and its mapping to a database. The first thing we obviously need to build a parsed representation is the source information to be parsed (annotated classes, hbm.xml files, orm.xml files). This is the purpose of org.hibernate.boot.MetadataSources.

MetadataSources has many other methods as well. Explore its API and Javadocs for more information. Also, all methods on MetadataSources offer fluent-style call chaining::

Example 326. Configuring a MetadataSources with method chaining
ServiceRegistry standardRegistry =
        new StandardServiceRegistryBuilder().build();

MetadataSources sources = new MetadataSources(standardRegistry)
    .addAnnotatedClass(MyEntity.class)
    .addAnnotatedClassName("org.hibernate.example.Customer")
    .addResource("org/hibernate/example/Order.hbm.xml")
    .addResource("org/hibernate/example/Product.orm.xml");

Once we have the sources of mapping information defined, we need to build the Metadata object. If you are ok with the default behavior in building the Metadata then you can simply call the buildMetadata method of the MetadataSources.

Notice that a ServiceRegistry can be passed at a number of points in this bootstrapping process. The suggested approach is to build a StandardServiceRegistry yourself and pass that along to the MetadataSources constructor. From there, MetadataBuilder, Metadata, SessionFactoryBuilder, and SessionFactory will all pick up that same StandardServiceRegistry.

However, if you wish to adjust the process of building Metadata from MetadataSources, you will need to use the MetadataBuilder as obtained via MetadataSources#getMetadataBuilder. MetadataBuilder allows a lot of control over the Metadata building process. See its Javadocs for full details.

Example 327. Building Metadata via MetadataBuilder
ServiceRegistry standardRegistry =
    new StandardServiceRegistryBuilder().build();

MetadataSources sources = new MetadataSources(standardRegistry);

MetadataBuilder metadataBuilder = sources.getMetadataBuilder();

// Use the JPA-compliant implicit naming strategy
metadataBuilder.applyImplicitNamingStrategy(
    ImplicitNamingStrategyJpaCompliantImpl.INSTANCE);

// specify the schema name to use for tables, etc when none is explicitly specified
metadataBuilder.applyImplicitSchemaName("my_default_schema");

// specify a custom Attribute Converter
metadataBuilder.applyAttributeConverter(myAttributeConverter);

Metadata metadata = metadataBuilder.build();

4.1.4. Building the SessionFactory

The final step in native bootstrapping is to build the SessionFactory itself. Much like discussed above, if you are ok with the default behavior of building a SessionFactory from a Metadata reference, you can simply call the buildSessionFactory method on the Metadata object.

However, if you would like to adjust that building process, you will need to use SessionFactoryBuilder as obtained via Metadata#getSessionFactoryBuilder. Again, see its Javadocs for more details.

Example 328. Native Bootstrapping - Putting it all together
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
    .configure("org/hibernate/example/hibernate.cfg.xml")
    .build();

Metadata metadata = new MetadataSources(standardRegistry)
    .addAnnotatedClass(MyEntity.class)
    .addAnnotatedClassName("org.hibernate.example.Customer")
    .addResource("org/hibernate/example/Order.hbm.xml")
    .addResource("org/hibernate/example/Product.orm.xml")
    .getMetadataBuilder()
    .applyImplicitNamingStrategy(ImplicitNamingStrategyJpaCompliantImpl.INSTANCE)
    .build();

SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
    .applyBeanManager(getBeanManager())
    .build();

The bootstrapping API is quite flexible, but in most cases it makes the most sense to think of it as a 3 step process:

  1. Build the StandardServiceRegistry

  2. Build the Metadata

  3. Use those 2 to build the SessionFactory

Example 329. Building SessionFactory via SessionFactoryBuilder
StandardServiceRegistry standardRegistry = new StandardServiceRegistryBuilder()
        .configure("org/hibernate/example/hibernate.cfg.xml")
        .build();

Metadata metadata = new MetadataSources(standardRegistry)
    .addAnnotatedClass(MyEntity.class)
    .addAnnotatedClassName("org.hibernate.example.Customer")
    .addResource("org/hibernate/example/Order.hbm.xml")
    .addResource("org/hibernate/example/Product.orm.xml")
    .getMetadataBuilder()
    .applyImplicitNamingStrategy(ImplicitNamingStrategyJpaCompliantImpl.INSTANCE)
    .build();

SessionFactoryBuilder sessionFactoryBuilder = metadata.getSessionFactoryBuilder();

// Supply a SessionFactory-level Interceptor
sessionFactoryBuilder.applyInterceptor(new CustomSessionFactoryInterceptor());

// Add a custom observer
sessionFactoryBuilder.addSessionFactoryObservers(new CustomSessionFactoryObserver());

// Apply a CDI BeanManager (for JPA event listeners)
sessionFactoryBuilder.applyBeanManager(getBeanManager());

SessionFactory sessionFactory = sessionFactoryBuilder.build();

4.2. Jakarta Persistence Bootstrapping

Bootstrapping Hibernate as a Jakarta Persistence provider can be done in a Jakarta Persistence-spec compliant manner or using a proprietary bootstrapping approach. The standardized approach has some limitations in certain environments, but aside from those, it is highly recommended that you use Jakarta Persistence-standardized bootstrapping.

4.2.1. Jakarta Persistence-compliant bootstrapping

In Jakarta Persistence, we are ultimately interested in bootstrapping a jakarta.persistence.EntityManagerFactory instance. The Jakarta Persistence specification defines two primary standardized bootstrap approaches depending on how the application intends to access the jakarta.persistence.EntityManager instances from an EntityManagerFactory.

It uses the terms EE and SE for these two approaches, but those terms are very misleading in this context. What the Jakarta Persistence spec calls EE bootstrapping implies the existence of a container (EE, OSGi, etc), who’ll manage and inject the persistence context on behalf of the application. What it calls SE bootstrapping is everything else. We will use the terms container-bootstrapping and application-bootstrapping in this guide.

For compliant container-bootstrapping, the container will build an EntityManagerFactory for each persistent-unit defined in the META-INF/persistence.xml configuration file and make that available to the application for injection via the jakarta.persistence.PersistenceUnit annotation or via JNDI lookup.

Example 330. Injecting the default EntityManagerFactory
@PersistenceUnit
private EntityManagerFactory emf;

Or, in case you have multiple Persistence Units (e.g. multiple persistence.xml configuration files), you can inject a specific EntityManagerFactory by Unit name:

Example 331. Injecting a specific EntityManagerFactory
 @PersistenceUnit(
     unitName = "CRM"
)
 private EntityManagerFactory entityManagerFactory;

The META-INF/persistence.xml file looks as follows:

Example 332. META-INF/persistence.xml configuration file
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

    <persistence-unit name="CRM">
        <description>
            Persistence unit for Hibernate User Guide
        </description>

        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <class>org.hibernate.documentation.userguide.Document</class>

        <properties>
            <property name="jakarta.persistence.jdbc.driver"
                      value="org.h2.Driver" />

            <property name="jakarta.persistence.jdbc.url"
                      value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1" />

            <property name="jakarta.persistence.jdbc.user"
                      value="sa" />

            <property name="jakarta.persistence.jdbc.password"
                      value="" />

            <property name="hibernate.show_sql"
                      value="true" />

            <property name="hibernate.hbm2ddl.auto"
                      value="update" />
        </properties>

    </persistence-unit>

</persistence>

For compliant application-bootstrapping, rather than the container building the EntityManagerFactory for the application, the application builds the EntityManagerFactory itself using the jakarta.persistence.Persistence bootstrap class. The application creates an EntityManagerFactory by calling the createEntityManagerFactory method:

Example 333. Application bootstrapped EntityManagerFactory
// Create an EMF for our CRM persistence-unit.
EntityManagerFactory emf = Persistence.createEntityManagerFactory("CRM");

If you don’t want to provide a persistence.xml configuration file, Jakarta Persistence allows you to provide all the configuration options in a PersistenceUnitInfo implementation and call HibernatePersistenceProvider.html#createContainerEntityManagerFactory.

To inject the default Persistence Context, you can use the @PersistenceContext annotation.

Example 334. Inject the default EntityManager
@PersistenceContext
private EntityManager em;

To inject a specific Persistence Context, you can use the @PersistenceContext annotation, and you can even pass EntityManager-specific properties using the @PersistenceProperty annotation.

Example 335. Inject a configurable EntityManager
 @PersistenceContext(
     unitName = "CRM",
     properties = {
         @PersistenceProperty(
             name="org.hibernate.flushMode",
             value= "MANUAL"
        )
     }
)
 private EntityManager entityManager;

If you would like additional details on accessing and using EntityManager instances, sections 7.6 and 7.7 of the Jakarta Persistence specification cover container-managed and application-managed EntityManagers, respectively.

4.2.2. Externalizing XML mapping files

Jakarta Persistence offers two mapping options:

  • annotations

  • XML mappings

Although annotations are much more common, there are projects where XML mappings are preferred. You can even mix annotations and XML mappings so that you can override annotation mappings with XML configurations that can be easily changed without recompiling the project source code. This is possible because if there are two conflicting mappings, the XML mappings take precedence over its annotation counterpart.

The Jakarta Persistence specification requires the XML mappings to be located on the classpath:

An object/relational mapping XML file named orm.xml may be specified in the META-INF directory in the root of the persistence unit or in the META-INF directory of any jar file referenced by the persistence.xml.

Alternatively, or in addition, one or more mapping files may be referenced by the mapping-file elements of the persistence-unit element. These mapping files may be present anywhere on the classpath.

— Section 8.2.1.6.2 of the Jakarta Persistence

Therefore, the mapping files can reside in the application jar artifacts, or they can be stored in an external folder location with the cogitation that that location be included in the classpath.

Hibernate is more lenient in this regard so you can use any external location even outside of the application configured classpath.

Example 336. META-INF/persistence.xml configuration file for external XML mappings
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

    <persistence-unit name="CRM">
        <description>
            Persistence unit for Hibernate User Guide
        </description>

        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <mapping-file>file:///etc/opt/app/mappings/orm.xml</mapping-file>

        <properties>
            <property name="jakarta.persistence.jdbc.driver"
                      value="org.h2.Driver" />

            <property name="jakarta.persistence.jdbc.url"
                      value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1" />

            <property name="jakarta.persistence.jdbc.user"
                      value="sa" />

            <property name="jakarta.persistence.jdbc.password"
                      value="" />

            <property name="hibernate.show_sql"
                      value="true" />

            <property name="hibernate.hbm2ddl.auto"
                      value="update" />
        </properties>

    </persistence-unit>

</persistence>

In the persistence.xml configuration file above, the orm.xml XML file containing all Jakarta Persistence entity mappings is located in the /etc/opt/app/mappings/ folder.

4.2.3. Configuring the SessionFactory Metadata via the Jakarta Persistence bootstrap

As previously seen, the Hibernate native bootstrap mechanism allows you to customize a great variety of configurations which are passed via the Metadata object.

When using Hibernate as a Jakarta Persistence provider, the EntityManagerFactory is backed by a SessionFactory. For this reason, you might still want to use the Metadata object to pass various settings which cannot be supplied via the standard Hibernate configuration settings.

For this reason, you can use the MetadataBuilderContributor class as you can see in the following examples.

Example 337. Implementing a MetadataBuilderContributor
public class SqlFunctionMetadataBuilderContributor
        implements MetadataBuilderContributor {

    @Override
    public void contribute(MetadataBuilder metadataBuilder) {
        metadataBuilder.applySqlFunction(
            "instr", new StandardSQLFunction( "instr", StandardBasicTypes.INTEGER )
        );
    }
}

org.hibernate.orm.test.bootstrap.spi.metadatabuildercontributor

The above MetadataBuilderContributor is used to register a SqlFuction which is not defined by the currently running Hibernate Dialect, but which we need to reference in our JPQL queries.

By having access to the MetadataBuilder class that’s used by the underlying SessionFactory, the Jakarta Persistence bootstrap becomes just as flexible as the Hibernate native bootstrap mechanism.

You can then pass the custom MetadataBuilderContributor via the hibernate.metadata_builder_contributor configuration property as explained in the Configuration chapter.

5. Schema Generation

Hibernate allows you to generate the database from the entity mappings.

Although the automatic schema generation is very useful for testing and prototyping purposes, in a production environment, it’s much more flexible to manage the schema using incremental migration scripts.

Traditionally, the process of generating schema from entity mapping has been called HBM2DDL. To get a list of Hibernate-native and Jakarta Persistence-specific configuration properties consider reading the Configurations section.

Considering the following Domain Model:

Example 338. Schema generation Domain Model
@Entity(name = "Customer")
public class Customer {

	@Id
	private Integer id;

	private String name;

	@Basic(fetch = FetchType.LAZY)
	private UUID accountsPayableXrefId;

	@Lob
	@Basic(fetch = FetchType.LAZY)
	@LazyGroup("lobs")
	private Blob image;

	//Getters and setters are omitted for brevity

}

@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@OneToMany(mappedBy = "author")
	private List<Book> books = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	@NaturalId
	private String isbn;

	@ManyToOne
	private Person author;

	//Getters and setters are omitted for brevity

}

If the hibernate.hbm2ddl.auto configuration is set to create, Hibernate is going to generate the following database schema:

Example 339. Auto-generated database schema
create table Customer (
    id integer not null,
    accountsPayableXrefId binary,
    image blob,
    name varchar(255),
    primary key (id)
)

create table Book (
    id bigint not null,
    isbn varchar(255),
    title varchar(255),
    author_id bigint,
    primary key (id)
)

create table Person (
    id bigint not null,
    name varchar(255),
    primary key (id)
)

alter table Book
    add constraint UK_u31e1frmjp9mxf8k8tmp990i unique (isbn)

alter table Book
    add constraint FKrxrgiajod1le3gii8whx2doie
    foreign key (author_id)
    references Person

5.1. Importing script files

To customize the schema generation process, the hibernate.hbm2ddl.import_files configuration property must be used to provide other scripts files that Hibernate can use when the SessionFactory is started.

For instance, considering the following schema-generation.sql import file:

Example 340. Schema generation import file
create sequence book_sequence start with 1 increment by 1

If we configure Hibernate to import the script above:

Example 341. Enabling schema generation import file
<property
    name="hibernate.hbm2ddl.import_files"
    value="schema-generation.sql" />

Hibernate is going to execute the script file after the schema is automatically generated.

5.2. Database objects

Hibernate allows you to customize the schema generation process via the HBM database-object element.

Considering the following HBM mapping:

Example 342. Schema generation HBM database-object
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd" >

<hibernate-mapping>
    <database-object>
        <create>
            CREATE OR REPLACE FUNCTION sp_count_books(
                IN authorId bigint,
                OUT bookCount bigint)
                RETURNS bigint AS
            $BODY$
                BEGIN
                    SELECT COUNT(*) INTO bookCount
                    FROM book
                    WHERE author_id = authorId;
                END;
            $BODY$
            LANGUAGE plpgsql;
        </create>
        <drop></drop>
        <dialect-scope name="org.hibernate.dialect.PostgreSQLDialect" />
    </database-object>
</hibernate-mapping>

When the SessionFactory is bootstrapped, Hibernate is going to execute the database-object, therefore creating the sp_count_books function.

5.3. Database-level checks

Hibernate offers the @Check annotation so that you can specify an arbitrary SQL CHECK constraint which can be defined as follows:

Example 343. Database check entity mapping example
@Entity(name = "Book")
@Check(name = "ValidIsbn", constraints = "CASE WHEN isbn IS NOT NULL THEN LENGTH(isbn) = 13 ELSE true END")
@SecondaryTable(name = "BookEdition")
@Check(name = "PositiveEdition", constraints = "edition > 0")
public static class Book {

	@Id
	private Long id;

	private String title;

	@NaturalId
	private String isbn;

	private Double price;

	@Column(table = "BookEdition")
	private int edition = 1;

	@Formula("edition + 1")
	private int nextEdition = 2;

	@Column(table = "BookEdition")
	private LocalDate editionDate;

	//Getters and setters omitted for brevity

}

Now, if you try to add a Book entity with an isbn attribute whose length is not 13 characters, a ConstraintViolationException is going to be thrown.

Example 344. Database check failure example
Book book = new Book();
book.setId(1L);
book.setPrice(49.99d);
book.setTitle("High-Performance Java Persistence");
book.setIsbn("11-11-2016");

entityManager.persist(book);
INSERT  INTO Book (isbn, price, title, id)
VALUES  ('11-11-2016', 49.99, 'High-Performance Java Persistence', 1)

-- WARN SqlExceptionHelper:129 - SQL Error: 0, SQLState: 23514
-- ERROR SqlExceptionHelper:131 - ERROR: new row for relation "book" violates check constraint "book_isbn_check"

5.4. Default value for a database column

With Hibernate, you can specify a default value for a given database column using the @ColumnDefault annotation.

Example 345. @ColumnDefault mapping example
@Entity(name = "Person")
@DynamicInsert
public static class Person {

    @Id
    private Long id;

    @ColumnDefault("'N/A'")
    private String name;

    @ColumnDefault("-1")
    private Long clientId;

    //Getter and setters omitted for brevity

}
CREATE TABLE Person (
  id BIGINT NOT NULL,
  clientId BIGINT DEFAULT -1,
  name VARCHAR(255) DEFAULT 'N/A',
  PRIMARY KEY (id)
)

In the mapping above, both the name and clientId table columns have a DEFAULT value.

The Person entity above is annotated with the @DynamicInsert annotation so that the INSERT statement does not include any entity attribute which is null.

This way, when the name and or clientId attribute is null, the database will set them according to their declared default values.

Example 346. @ColumnDefault mapping example
doInJPA(this::entityManagerFactory, entityManager -> {
    Person person = new Person();
    person.setId(1L);
    entityManager.persist(person);
});
doInJPA(this::entityManagerFactory, entityManager -> {
    Person person = entityManager.find(Person.class, 1L);
    assertEquals("N/A", person.getName());
    assertEquals(Long.valueOf(-1L), person.getClientId());
});
INSERT INTO Person (id) VALUES (?)

If the column value should be generated not only when a row is inserted, but also when it’s updated, the @GeneratedColumn annotation should be used.

5.5. Columns unique constraint

The @UniqueConstraint annotation is used to specify a unique constraint to be included by the automated schema generator for the primary or secondary table associated with the current annotated entity.

Considering the following entity mapping, Hibernate generates the unique constraint DDL when creating the database schema:

Example 347. @UniqueConstraint mapping example
 @Entity
 @Table(
     name = "book",
     uniqueConstraints =  @UniqueConstraint(
         name = "uk_book_title_author",
         columnNames = {
             "title",
             "author_id"
         }
    )
)
 public static class Book {

     @Id
     @GeneratedValue
     private Long id;

     private String title;

     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(
         name = "author_id",
         foreignKey = @ForeignKey(name = "fk_book_author_id")
    )
     private Author author;

     //Getter and setters omitted for brevity
 }

 @Entity
 @Table(name = "author")
 public static class Author {

     @Id
     @GeneratedValue
     private Long id;

     @Column(name = "first_name")
     private String firstName;

     @Column(name = "last_name")
     private String lastName;

     //Getter and setters omitted for brevity
 }
create table author (
    id bigint not null,
    first_name varchar(255),
    last_name varchar(255),
    primary key (id)
)

create table book (
    id bigint not null,
    title varchar(255),
    author_id bigint,
    primary key (id)
)

alter table book
   add constraint uk_book_title_author
   unique (title, author_id)

alter table book
   add constraint fk_book_author_id
   foreign key (author_id)
   references author

With the uk_book_title_author unique constraint in place, it’s no longer possible to add two books with the same title and for the same author.

Example 348. @UniqueConstraintTest persist example
     Author _author = doInJPA(this::entityManagerFactory, entityManager -> {
         Author author = new Author();
         author.setFirstName("Vlad");
         author.setLastName("Mihalcea");
         entityManager.persist(author);

         Book book = new Book();
         book.setTitle("High-Performance Java Persistence");
         book.setAuthor(author);
         entityManager.persist(book);

         return author;
     });

     try {
         doInJPA(this::entityManagerFactory, entityManager -> {
	Book book = new Book();
	book.setTitle("High-Performance Java Persistence");
	book.setAuthor(_author);
	entityManager.persist(book);
});
     }
     catch (Exception expected) {
         assertNotNull(ExceptionUtil.findCause(expected, ConstraintViolationException.class));
     }
insert
into
    author
    (first_name, last_name, id)
values
    (?, ?, ?)

-- binding parameter [1] as [VARCHAR] - [Vlad]
-- binding parameter [2] as [VARCHAR] - [Mihalcea]
-- binding parameter [3] as [BIGINT]  - [1]

insert
into
    book
    (author_id, title, id)
values
    (?, ?, ?)

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT]  - [2]

insert
into
    book
    (author_id, title, id)
values
    (?, ?, ?)

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [BIGINT]  - [3]

-- SQL Error: 23505, SQLState: 23505
-- Unique index or primary key violation: "UK_BOOK_TITLE_AUTHOR_INDEX_1 ON PUBLIC.BOOK(TITLE, AUTHOR_ID) VALUES ( /* key:1 */ 3, 'High-Performance Java Persistence', 1)";

The second INSERT statement fails because of the unique constraint violation.

5.6. Columns index

The @Index annotation is used by the automated schema generation tool to create a database index.

Creating unique index containing all primary key columns will result in ordering primary key columns specified by columnList

Considering the following entity mapping. Hibernate generates the index when creating the database schema:

Example 349. @Index mapping example
 @Entity
 @Table(
     name = "author",
     indexes =  @Index(
         name = "idx_author_first_last_name",
         columnList = "first_name, last_name",
         unique = false
    )
)
 public static class Author {

     @Id
     @GeneratedValue
     private Long id;

     @Column(name = "first_name")
     private String firstName;

     @Column(name = "last_name")
     private String lastName;

     //Getter and setters omitted for brevity
 }
create table author (
    id bigint not null,
    first_name varchar(255),
    last_name varchar(255),
    primary key (id)
)

create index idx_author_first_last_name
    on author (first_name, last_name)

6. Persistence Context

Both the org.hibernate.Session API and jakarta.persistence.EntityManager API represent a context for dealing with persistent data. This concept is called a persistence context. Persistent data has a state in relation to both a persistence context and the underlying database.

transient

the entity has just been instantiated and is not associated with a persistence context. It has no persistent representation in the database and typically no identifier value has been assigned (unless the assigned generator was used).

managed or persistent

the entity has an associated identifier and is associated with a persistence context. It may or may not physically exist in the database yet.

detached

the entity has an associated identifier but is no longer associated with a persistence context (usually because the persistence context was closed or the instance was evicted from the context)

removed

the entity has an associated identifier and is associated with a persistence context, however, it is scheduled for removal from the database.

Much of the org.hibernate.Session and jakarta.persistence.EntityManager methods deal with moving entities among these states.

6.1. Accessing Hibernate APIs from Jakarta Persistence

Jakarta Persistence defines an incredibly useful method to allow applications access to the APIs of the underlying provider.

Example 350. Accessing Hibernate APIs from Jakarta Persistence
Session session = entityManager.unwrap(Session.class);
SessionImplementor sessionImplementor = entityManager.unwrap(SessionImplementor.class);

SessionFactory sessionFactory = entityManager.getEntityManagerFactory().unwrap(SessionFactory.class);

6.2. Bytecode Enhancement

Hibernate "grew up" not supporting bytecode enhancement at all. At that time, Hibernate only supported proxy-based alternative for lazy loading and always used diff-based dirty calculation. Hibernate 3.x saw the first attempts at bytecode enhancement support in Hibernate. We consider those initial attempts (up until 5.0) completely as an incubation. The support for bytecode enhancement in 5.0 onward is what we are discussing here.

See Bytecode Enhancement for discussion of performing enhancement.

6.2.1. Lazy attribute loading

Think of this as partial loading support. Essentially, you can tell Hibernate that only part(s) of an entity should be loaded upon fetching from the database and when the other part(s) should be loaded as well. Note that this is very much different from the proxy-based idea of lazy loading which is entity-centric where the entity’s state is loaded at once as needed. With bytecode enhancement, individual attributes or groups of attributes are loaded as needed.

Lazy attributes can be designated to be loaded together, and this is called a "lazy group". By default, all singular attributes are part of a single group, meaning that when one lazy singular attribute is accessed all lazy singular attributes are loaded. Lazy plural attributes, by default, are each a lazy group by themselves. This behavior is explicitly controllable through the @org.hibernate.annotations.LazyGroup annotation.

Example 351. @LazyGroup example
@Entity
public class Customer {

	@Id
	private Integer id;

	private String name;

	@Basic(fetch = FetchType.LAZY)
	private UUID accountsPayableXrefId;

	@Lob
	@Basic(fetch = FetchType.LAZY)
	@LazyGroup("lobs")
	private Blob image;

	//Getters and setters are omitted for brevity

}

In the above example, we have 2 lazy attributes: accountsPayableXrefId and image. Each is part of a different fetch group (accountsPayableXrefId is part of the default fetch group), which means that accessing accountsPayableXrefId will not force the loading of the image attribute, and vice-versa.

As a hopefully temporary legacy hold-over, it is currently required that all lazy singular associations (many-to-one and one-to-one) also include @LazyToOne(LazyToOneOption.NO_PROXY). The plan is to relax that requirement later.

6.2.2. In-line dirty tracking

Historically Hibernate only supported diff-based dirty calculation for determining which entities in a persistence context have changed. This essentially means that Hibernate would keep track of the last known state of an entity in regards to the database (typically the last read or write). Then, as part of flushing the persistence context, Hibernate would walk every entity associated with the persistence context and check its current state against that "last known database state". This is by far the most thorough approach to dirty checking because it accounts for data-types that can change their internal state (java.util.Date is the prime example of this). However, in a persistence context with a large number of associated entities, it can also be a performance-inhibiting approach.

If your application does not need to care about "internal state changing data-type" use cases, bytecode-enhanced dirty tracking might be a worthwhile alternative to consider, especially in terms of performance. In this approach Hibernate will manipulate the bytecode of your classes to add "dirty tracking" directly to the entity, allowing the entity itself to keep track of which of its attributes have changed. During the flush time, Hibernate asks your entity what has changed rather than having to perform the state-diff calculations.

6.2.3. Bidirectional association management

Hibernate strives to keep your application as close to "normal Java usage" (idiomatic Java) as possible. Consider a domain model with a normal Person/Book bidirectional association:

Example 352. Bidirectional association
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@OneToMany(mappedBy = "author")
	private List<Book> books = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	@NaturalId
	private String isbn;

	@ManyToOne
	private Person author;

	//Getters and setters are omitted for brevity

}
Example 353. Incorrect normal Java usage
Person person = new Person();
person.setName("John Doe");

Book book = new Book();
person.getBooks().add(book);
try {
	book.getAuthor().getName();
}
catch (NullPointerException expected) {
	// This blows up (NPE) in normal Java usage
}

This blows up in normal Java usage. The correct normal Java usage is:

Example 354. Correct normal Java usage
Person person = new Person();
person.setName("John Doe");

Book book = new Book();
person.getBooks().add(book);
book.setAuthor(person);

book.getAuthor().getName();

Bytecode-enhanced bi-directional association management makes that first example work by managing the "other side" of a bi-directional association whenever one side is manipulated.

6.2.4. Internal performance optimizations

Additionally, we use the enhancement process to add some additional code that allows us to optimize certain performance characteristics of the persistence context. These are hard to discuss without diving into a discussion of Hibernate internals.

6.3. Making entities persistent

Once you’ve created a new entity instance (using the standard new operator) it is in new state. You can make it persistent by associating it to either an org.hibernate.Session or a jakarta.persistence.EntityManager.

Example 355. Making an entity persistent with Jakarta Persistence
Person person = new Person();
person.setId(1L);
person.setName("John Doe");

entityManager.persist(person);
Example 356. Making an entity persistent with Hibernate API
Person person = new Person();
person.setId(1L);
person.setName("John Doe");

session.persist(person);

org.hibernate.Session also has a method named persist which follows the exact semantics defined in the Jakarta Persistence specification for the persist method. It is this org.hibernate.Session method to which the Hibernate jakarta.persistence.EntityManager implementation delegates.

If the DomesticCat entity type has a generated identifier, the value is associated with the instance when the save or persist is called. If the identifier is not automatically generated, the manually assigned (usually natural) key value has to be set on the instance before the save or persist methods are called.

6.4. Deleting (removing) entities

Entities can also be deleted.

Example 357. Deleting an entity with Jakarta Persistence
entityManager.remove(person);
Example 358. Deleting an entity with the Hibernate API
session.remove(person);

Hibernate itself can handle deleting entities in detached state. Jakarta Persistence, however, disallows this behavior.

The implication here is that the entity instance passed to the org.hibernate.Session delete method can be either in managed or detached state, while the entity instance passed to remove on jakarta.persistence.EntityManager must be in the managed state.

6.5. Obtain an entity reference without initializing its data

Sometimes referred to as lazy loading, the ability to obtain a reference to an entity without having to load its data is hugely important. The most common case being the need to create an association between an entity and another existing entity.

Example 359. Obtaining an entity reference without initializing its data with Jakarta Persistence
Book book = new Book();
book.setAuthor(entityManager.getReference(Person.class, personId));
Example 360. Obtaining an entity reference without initializing its data with Hibernate API
Book book = new Book();
book.setId(1L);
book.setIsbn("123-456-7890");
entityManager.persist(book);
book.setAuthor(session.getReference(Person.class, personId));

The above works on the assumption that the entity is defined to allow lazy loading, generally through use of runtime proxies. In both cases an exception will be thrown later if the given entity does not refer to actual database state when the application attempts to use the returned proxy in any way that requires access to its data.

Unless the entity class is declared final, the proxy extends the entity class. If the entity class is final, the proxy will implement an interface instead. See the @Proxy mapping section for more info.

6.6. Obtain an entity with its data initialized

It is also quite common to want to obtain an entity along with its data (e.g. like when we need to display it in the UI).

Example 361. Obtaining an entity reference with its data initialized with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
Example 362. Obtaining an entity reference with its data initialized with Hibernate API
Person person = session.get(Person.class, personId);
Example 363. Obtaining an entity reference with its data initialized using the byId() Hibernate API
Person person = session.byId(Person.class).load(personId);

In both cases null is returned if no matching database row was found.

It’s possible to return a Java 8 Optional as well:

Example 364. Obtaining an Optional entity reference with its data initialized using the byId() Hibernate API
Optional<Person> optionalPerson = session.byId(Person.class).loadOptional(personId);

6.7. Obtain multiple entities by their identifiers

If you want to load multiple entities by providing their identifiers, calling the EntityManager#find method multiple times is not only inconvenient, but also inefficient.

While the Jakarta Persistence standard does not support retrieving multiple entities at once, other than running a JPQL or Criteria API query, Hibernate offers this functionality via the byMultipleIds method of the Hibernate Session.

The byMultipleIds method returns a MultiIdentifierLoadAccess which you can use to customize the multi-load request.

The MultiIdentifierLoadAccess interface provides several methods which you can use to change the behavior of the multi-load call:

enableOrderedReturn(boolean enabled)

This setting controls whether the returned List is ordered and positional in relation to the incoming ids. If enabled (the default), the return List is ordered and positional relative to the incoming ids. In other words, a request to multiLoad([2,1,3]) will return [Entity#2, Entity#1, Entity#3].

An important distinction is made here in regards to the handling of unknown entities depending on this "ordered return" setting. If enabled, a null is inserted into the List at the proper position(s). If disabled, the nulls are not put into the return List.

In other words, consumers of the returned ordered List would need to be able to handle null elements.

enableSessionCheck(boolean enabled)

This setting, which is disabled by default, tells Hibernate to check the first-level cache (a.k.a Session or Persistence Context) first and, if the entity is found and already managed by the Hibernate Session, the cached entity will be added to the returned List, therefore skipping it from being fetched via the multi-load query.

enableReturnOfDeletedEntities(boolean enabled)

This setting instructs Hibernate if the multi-load operation is allowed to return entities that were deleted by the current Persistence Context. A deleted entity is one which has been passed to this Session.delete or Session.remove method, but the Session was not flushed yet, meaning that the associated row was not deleted in the database table.

The default behavior is to handle them as null in the return (see enableOrderedReturn). When enabled, the result set will contain deleted entities. When disabled (which is the default behavior), deleted entities are not included in the returning List.

with(LockOptions lockOptions)

This setting allows you to pass a given LockOptions mode to the multi-load query.

with(CacheMode cacheMode)

This setting allows you to pass a given CacheMode strategy so that we can load entities from the second-level cache, therefore skipping the cached entities from being fetched via the multi-load query.

withBatchSize(int batchSize)

This setting allows you to specify a batch size for loading the entities (e.g. how many at a time).

The default is to use a batch sizing strategy defined by the Dialect.getDefaultBatchLoadSizingStrategy() method.

Any greater-than-one value here will override that default behavior.

with(RootGraph<T> graph)

The RootGraph is a Hibernate extension to the Jakarta Persistence EntityGraph contract, and this method allows you to pass a specific RootGraph to the multi-load query so that it can fetch additional relationships of the current loading entity.

Now, assuming we have 3 Person entities in the database, we can load all of them with a single call as illustrated by the following example:

Example 365. Loading multiple entities using the byMultipleIds() Hibernate API
Session session = entityManager.unwrap( Session.class );

List<Person> persons = session
		.byMultipleIds( Person.class )
		.multiLoad( 1L, 2L, 3L );

assertEquals( 3, persons.size() );

List<Person> samePersons = session
		.byMultipleIds( Person.class )
		.enableSessionCheck( true )
		.multiLoad( 1L, 2L, 3L );

assertEquals( persons, samePersons );
SELECT p.id AS id1_0_0_,
       p.name AS name2_0_0_
FROM   Person p
WHERE  p.id IN ( 1, 2, 3 )

Notice that only one SQL SELECT statement was executed since the second call uses the enableSessionCheck method of the MultiIdentifierLoadAccess to instruct Hibernate to skip entities that are already loaded in the current Persistence Context.

If the entities are not available in the current Persistence Context but they could be loaded from the second-level cache, you can use the with(CacheMode) method of the MultiIdentifierLoadAccess object.

Example 366. Loading multiple entities from the second-level cache
SessionFactory sessionFactory = scope.getEntityManagerFactory().unwrap(SessionFactory.class);
Statistics statistics = sessionFactory.getStatistics();

sessionFactory.getCache().evictAll();
statistics.clear();
final SQLStatementInspector sqlStatementInspector = scope.getStatementInspector( SQLStatementInspector.class );
sqlStatementInspector.clear();

assertEquals(0, statistics.getQueryExecutionCount());

scope.inTransaction(
		entityManager -> {
			Session session = entityManager.unwrap(Session.class);

			List<Person> persons = session
					.byMultipleIds(Person.class)
					.multiLoad(1L, 2L, 3L);

			assertEquals(3, persons.size());
		}
);

assertEquals(0, statistics.getSecondLevelCacheHitCount());
assertEquals(3, statistics.getSecondLevelCachePutCount());
assertEquals(1, sqlStatementInspector.getSqlQueries().size());

scope.inTransaction(
		entityManager -> {
			Session session = entityManager.unwrap(Session.class);
			sqlStatementInspector.clear();

			List<Person> persons = session.byMultipleIds(Person.class)
				.with(CacheMode.NORMAL)
				.multiLoad(1L, 2L, 3L);

			assertEquals(3, persons.size());
		}
);

assertEquals(3, statistics.getSecondLevelCacheHitCount());
assertEquals(0, sqlStatementInspector.getSqlQueries().size());

In the example above, we first make sure that we clear the second-level cache to demonstrate that the multi-load query will put the returning entities into the second-level cache.

After executing the first byMultipleIds call, Hibernate is going to fetch the requested entities, and as illustrated by the getSecondLevelCachePutCount method call, 3 entities were indeed added to the shared cache.

Afterward, when executing the second byMultipleIds call for the same entities in a new Hibernate Session, we set the CacheMode.NORMAL second-level cache mode so that entities are going to be returned from the second-level cache.

The getSecondLevelCacheHitCount statistics method returns 3 this time, since the 3 entities were loaded from the second-level cache, and, as illustrated by sqlStatementInterceptor.getSqlQueries(), no multi-load SELECT statement was executed this time.

6.8. Obtain an entity by natural-id

In addition to allowing to load the entity by its identifier, Hibernate allows applications to load entities by the declared natural identifier.

Example 367. Natural-id mapping
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	@NaturalId
	private String isbn;

	@ManyToOne
	private Person author;

	//Getters and setters are omitted for brevity

}

We can also opt to fetch the entity or just retrieve a reference to it when using the natural identifier loading methods.

Example 368. Get entity reference by simple natural-id
Book book = session.bySimpleNaturalId(Book.class).getReference(isbn);
Example 369. Load entity by natural-id
Book book = session
	.byNaturalId(Book.class)
	.using("isbn", isbn)
	.load();

We can also use a Java 8 Optional to load an entity by its natural id:

Example 370. Load an Optional entity by natural-id
Optional<Book> optionalBook = session
	.byNaturalId(Book.class)
	.using("isbn", isbn)
	.loadOptional();

Hibernate offers a consistent API for accessing persistent data by identifier or by the natural-id. Each of these defines the same two data access methods:

getReference

Should be used in cases where the identifier is assumed to exist, where non-existence would be an actual error. Should never be used to test existence. That is because this method will prefer to create and return a proxy if the data is not already associated with the Session rather than hit the database. The quintessential use-case for using this method is to create foreign key based associations.

load

Will return the persistent data associated with the given identifier value or null if that identifier does not exist.

Each of these two methods defines an overloading variant accepting a org.hibernate.LockOptions argument. Locking is discussed in a separate chapter.

6.9. Filtering entities and associations

Hibernate offers two options if you want to filter entities or entity associations:

static (e.g. @SQLRestriction and @SQLJoinTableRestriction)

which are defined at mapping time and cannot change at runtime.

dynamic (e.g. @Filter and @FilterJoinTable)

which are applied and configured at runtime.

6.9.1. @SQLRestriction

Sometimes, you want to filter out entities or collections using custom SQL criteria. This can be achieved using the @SQLRestriction annotation, which can be applied to entities and collections.

Example 371. @SQLRestriction mapping usage
public enum AccountType {
	DEBIT,
	CREDIT
}

@Entity(name = "Client")
public static class Client {

	@Id
	private Long id;

	private String name;

	@SQLRestriction("account_type = 'DEBIT'")
	@OneToMany(mappedBy = "client")
	private List<Account> debitAccounts = new ArrayList<>();

	@SQLRestriction("account_type = 'CREDIT'")
	@OneToMany(mappedBy = "client")
	private List<Account> creditAccounts = new ArrayList<>();

	//Getters and setters omitted for brevity

}

@Entity(name = "Account")
@SQLRestriction("active = true")
public static class Account {

	@Id
	private Long id;

	@ManyToOne
	private Client client;

	@Column(name = "account_type")
	@Enumerated(EnumType.STRING)
	private AccountType type;

	private Double amount;

	private Double rate;

	private boolean active;

	//Getters and setters omitted for brevity

}

If the database contains the following entities:

Example 372. Persisting and fetching entities with a @SQLRestriction mapping
doInJPA(this::entityManagerFactory, entityManager -> {

	Client client = new Client();
	client.setId(1L);
	client.setName("John Doe");
	entityManager.persist(client);

	Account account1 = new Account();
	account1.setId(1L);
	account1.setType(AccountType.CREDIT);
	account1.setAmount(5000d);
	account1.setRate(1.25 / 100);
	account1.setActive(true);
	account1.setClient(client);
	client.getCreditAccounts().add(account1);
	entityManager.persist(account1);

	Account account2 = new Account();
	account2.setId(2L);
	account2.setType(AccountType.DEBIT);
	account2.setAmount(0d);
	account2.setRate(1.05 / 100);
	account2.setActive(false);
	account2.setClient(client);
	client.getDebitAccounts().add(account2);
	entityManager.persist(account2);

	Account account3 = new Account();
	account3.setType(AccountType.DEBIT);
	account3.setId(3L);
	account3.setAmount(250d);
	account3.setRate(1.05 / 100);
	account3.setActive(true);
	account3.setClient(client);
	client.getDebitAccounts().add(account3);
	entityManager.persist(account3);
});
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)

INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (true, 5000.0, 1, 0.0125, 'CREDIT', 1)

INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (false, 0.0, 1, 0.0105, 'DEBIT', 2)

INSERT INTO Account (active, amount, client_id, rate, account_type, id)
VALUES (true, 250.0, 1, 0.0105, 'DEBIT', 3)

When executing an Account entity query, Hibernate is going to filter out all records that are not active.

Example 373. Query entities mapped with @SQLRestriction
doInJPA(this::entityManagerFactory, entityManager -> {
	List<Account> accounts = entityManager.createQuery(
		"select a from Account a", Account.class)
	.getResultList();
	assertEquals(2, accounts.size());
});
SELECT
    a.id as id1_0_,
    a.active as active2_0_,
    a.amount as amount3_0_,
    a.client_id as client_i6_0_,
    a.rate as rate4_0_,
    a.account_type as account_5_0_
FROM
    Account a
WHERE ( a.active = true )

When fetching the debitAccounts or the creditAccounts collections, Hibernate is going to apply the @SQLRestriction clause filtering criteria to the associated child entities.

Example 374. Traversing collections mapped with @SQLRestriction
doInJPA(this::entityManagerFactory, entityManager -> {
	Client client = entityManager.find(Client.class, 1L);
	assertEquals(1, client.getCreditAccounts().size());
	assertEquals(1, client.getDebitAccounts().size());
});
SELECT
    c.client_id as client_i6_0_0_,
    c.id as id1_0_0_,
    c.id as id1_0_1_,
    c.active as active2_0_1_,
    c.amount as amount3_0_1_,
    c.client_id as client_i6_0_1_,
    c.rate as rate4_0_1_,
    c.account_type as account_5_0_1_
FROM
    Account c
WHERE ( c.active = true and c.account_type = 'CREDIT' ) AND c.client_id = 1

SELECT
    d.client_id as client_i6_0_0_,
    d.id as id1_0_0_,
    d.id as id1_0_1_,
    d.active as active2_0_1_,
    d.amount as amount3_0_1_,
    d.client_id as client_i6_0_1_,
    d.rate as rate4_0_1_,
    d.account_type as account_5_0_1_
FROM
    Account d
WHERE ( d.active = true and d.account_type = 'DEBIT' ) AND d.client_id = 1

6.9.2. @SQLJoinTableRestriction

Just like @SQLRestriction annotation, @SQLJoinTableRestriction is used to filter out collections using a joined table (e.g. @ManyToMany association).

Example 375. @SQLJoinTableRestriction mapping example
@Entity(name = "Book")
public static class Book {

	@Id
	private Long id;

	private String title;

	private String author;

	@ManyToMany
	@JoinTable(
		name = "Book_Reader",
		joinColumns = @JoinColumn(name = "book_id"),
		inverseJoinColumns = @JoinColumn(name = "reader_id")
	)
	@SQLJoinTableRestriction("created_on > DATEADD('DAY', -7, CURRENT_TIMESTAMP())")
	private List<Reader> currentWeekReaders = new ArrayList<>();

	//Getters and setters omitted for brevity

}

@Entity(name = "Reader")
public static class Reader {

	@Id
	private Long id;

	private String name;

	//Getters and setters omitted for brevity

}
create table Book (
    id bigint not null,
    author varchar(255),
    title varchar(255),
    primary key (id)
)

create table Book_Reader (
    book_id bigint not null,
    reader_id bigint not null
)

create table Reader (
    id bigint not null,
    name varchar(255),
    primary key (id)
)

alter table Book_Reader
    add constraint FKsscixgaa5f8lphs9bjdtpf9g
    foreign key (reader_id)
    references Reader

alter table Book_Reader
    add constraint FKoyrwu9tnwlukd1616qhck21ra
    foreign key (book_id)
    references Book

alter table Book_Reader
    add created_on timestamp
    default current_timestamp

In the example above, the current week Reader entities are included in the currentWeekReaders collection which uses the @SQLJoinTableRestriction annotation to filter the joined table rows according to the provided SQL clause.

Considering that the following two Book_Reader entries are added into our system:

Example 376. @SQLJoinTableRestriction test data
Book book = new Book();
book.setId(1L);
book.setTitle("High-Performance Java Persistence");
book.setAuthor("Vad Mihalcea");
entityManager.persist(book);

Reader reader1 = new Reader();
reader1.setId(1L);
reader1.setName("John Doe");
entityManager.persist(reader1);

Reader reader2 = new Reader();
reader2.setId(2L);
reader2.setName("John Doe Jr.");
entityManager.persist(reader2);

statement.executeUpdate(
	"INSERT INTO Book_Reader " +
	"	(book_id, reader_id) " +
	"VALUES " +
	"	(1, 1) "
);
statement.executeUpdate(
	"INSERT INTO Book_Reader " +
	"	(book_id, reader_id, created_on) " +
	"VALUES " +
	"	(1, 2, DATEADD('DAY', -10, CURRENT_TIMESTAMP())) "
);

When fetching the currentWeekReaders collection, Hibernate is going to find only one entry:

Example 377. @SQLJoinTableRestriction fetch example
Book book = entityManager.find(Book.class, 1L);
assertEquals(1, book.getCurrentWeekReaders().size());

6.9.3. @Filter

The @Filter annotation is another way to filter out entities or collections using custom SQL criteria. Unlike the @SQLRestriction annotation, @Filter allows you to parameterize the filter clause at runtime.

Now, considering we have the following Account entity:

Example 378. @Filter mapping entity-level usage
 @Entity(name = "Account")
 @Table(name = "account")
 @FilterDef(
     name="activeAccount",
     parameters = @ParamDef(
         name="active",
         type=Boolean.class
    )
)
 @Filter(
     name="activeAccount",
     condition="active_status = :active"
)
 public static class Account {

     @Id
     private Long id;

     @ManyToOne(fetch = FetchType.LAZY)
     private Client client;

     @Column(name = "account_type")
     @Enumerated(EnumType.STRING)
     private AccountType type;

     private Double amount;

     private Double rate;

     @Column(name = "active_status")
     private boolean active;

     //Getters and setters omitted for brevity
 }

Notice that the active property is mapped to the active_status column.

This mapping was done to show you that the @Filter condition uses a SQL condition and not a JPQL filtering predicate.

As already explained, we can also apply the @Filter annotation for collections as illustrated by the Client entity:

Example 379. @Filter mapping collection-level usage
@Entity(name = "Client")
@Table(name = "client")
public static class Client {

    @Id
    private Long id;

    private String name;

    private AccountType type;

    @OneToMany(
        mappedBy = "client",
        cascade = CascadeType.ALL
   )
    @Filter(
        name="activeAccount",
        condition="active_status = :active"
   )
    private List<Account> accounts = new ArrayList<>();

    //Getters and setters omitted for brevity

    public void addAccount(Account account) {
        account.setClient(this);
        this.accounts.add(account);
    }
}

If we persist a Client with three associated Account entities, Hibernate will execute the following SQL statements:

Example 380. Persisting and fetching entities with a @Filter mapping
 Client client = new Client()
 .setId(1L)
 .setName("John Doe")
 .setType(AccountType.DEBIT);

 client.addAccount(
     new Account()
     .setId(1L)
     .setType(AccountType.CREDIT)
     .setAmount(5000d)
     .setRate(1.25 / 100)
     .setActive(true)
);

 client.addAccount(
     new Account()
     .setId(2L)
     .setType(AccountType.DEBIT)
     .setAmount(0d)
     .setRate(1.05 / 100)
     .setActive(false)
);

 client.addAccount(
     new Account()
     .setType(AccountType.DEBIT)
     .setId(3L)
     .setAmount(250d)
     .setRate(1.05 / 100)
     .setActive(true)
);

 entityManager.persist(client);
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)

INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (true, 5000.0, 1, 0.0125, 'CREDIT', 1)

INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (false, 0.0, 1, 0.0105, 'DEBIT', 2)

INSERT INTO Account (active_status, amount, client_id, rate, account_type, id)
VALUES (true, 250.0, 1, 0.0105, 'DEBIT', 3)

By default, without explicitly enabling the filter, Hibernate is going to fetch all Account entities.

Example 381. Query entities mapped without activating the @Filter
List<Account> accounts = entityManager.createQuery(
    "select a from Account a", Account.class)
.getResultList();

assertEquals(3, accounts.size());
SELECT
    a.id as id1_0_,
    a.active_status as active2_0_,
    a.amount as amount3_0_,
    a.client_id as client_i6_0_,
    a.rate as rate4_0_,
    a.account_type as account_5_0_
FROM
    Account a

If the filter is enabled and the filter parameter value is provided, then Hibernate is going to apply the filtering criteria to the associated Account entities.

Example 382. Query entities mapped with @Filter
entityManager
    .unwrap(Session.class)
    .enableFilter("activeAccount")
    .setParameter("active", true);

List<Account> accounts = entityManager.createQuery(
    "select a from Account a", Account.class)
.getResultList();

assertEquals(2, accounts.size());
SELECT
    a.id as id1_0_,
    a.active_status as active2_0_,
    a.amount as amount3_0_,
    a.client_id as client_i6_0_,
    a.rate as rate4_0_,
    a.account_type as account_5_0_
FROM
    Account a
WHERE
    a.active_status = true

Filters apply to entity queries, but not to direct fetching.

Therefore, in the following example, the filter is not taken into consideration when fetching an entity from the Persistence Context.

Fetching entities mapped with @Filter
entityManager
    .unwrap(Session.class)
    .enableFilter("activeAccount")
    .setParameter("active", true);

Account account = entityManager.find(Account.class, 2L);

assertFalse( account.isActive() );
SELECT
    a.id as id1_0_0_,
    a.active_status as active2_0_0_,
    a.amount as amount3_0_0_,
    a.client_id as client_i6_0_0_,
    a.rate as rate4_0_0_,
    a.account_type as account_5_0_0_,
    c.id as id1_1_1_,
    c.name as name2_1_1_
FROM
    Account a
WHERE
    a.id = 2

As you can see from the example above, contrary to an entity query, the filter does not prevent the entity from being loaded.

Just like with entity queries, collections can be filtered as well, but only if the filter is explicitly enabled on the currently running Hibernate Session.

Example 383. Traversing collections without activating the @Filter
Client client = entityManager.find(Client.class, 1L);

assertEquals(3, client.getAccounts().size());
SELECT
    c.id as id1_1_0_,
    c.name as name2_1_0_
FROM
    Client c
WHERE
    c.id = 1

SELECT
    a.id as id1_0_,
    a.active_status as active2_0_,
    a.amount as amount3_0_,
    a.client_id as client_i6_0_,
    a.rate as rate4_0_,
    a.account_type as account_5_0_
FROM
    Account a
WHERE
    a.client_id = 1

When activating the @Filter and fetching the accounts collections, Hibernate is going to apply the filter condition to the associated collection entries.

Example 384. Traversing collections mapped with @Filter
entityManager
    .unwrap(Session.class)
    .enableFilter("activeAccount")
    .setParameter("active", true);

Client client = entityManager.find(Client.class, 1L);

assertEquals(2, client.getAccounts().size());
SELECT
    c.id as id1_1_0_,
    c.name as name2_1_0_
FROM
    Client c
WHERE
    c.id = 1

SELECT
    a.id as id1_0_,
    a.active_status as active2_0_,
    a.amount as amount3_0_,
    a.client_id as client_i6_0_,
    a.rate as rate4_0_,
    a.account_type as account_5_0_
FROM
    Account a
WHERE
    accounts0_.active_status = true
    and a.client_id = 1

The main advantage of @Filter over the @SQLRestriction clause is that the filtering criteria can be customized at runtime.

It’s not possible to combine the @Filter and @Cache collection annotations. This limitation is due to ensuring consistency and because the filtering information is not stored in the second-level cache.

If caching were allowed for a currently filtered collection, then the second-level cache would store only a subset of the whole collection. Afterward, every other Session will get the filtered collection from the cache, even if the Session-level filters have not been explicitly activated.

For this reason, the second-level collection cache is limited to storing whole collections, and not subsets.

6.9.4. @Filter with @SqlFragmentAlias

When using the @Filter annotation and working with entities that are mapped onto multiple database tables, you will need to use the @SqlFragmentAlias annotation if the @Filter defines a condition that uses predicates across multiple tables.

Example 385. @SqlFragmentAlias mapping usage
@Entity(name = "Account")
@Table(name = "account")
@Comment(on="account", value = "The account table")
@SecondaryTable(
	name = "account_details"
)
@Comment(on="account_details", value = "The account details secondary table")
@SQLDelete(
	sql = "UPDATE account_details SET deleted = true WHERE id = ? "
)
@FilterDef(
	name="activeAccount",
	parameters = @ParamDef(
		name="active",
		type=Boolean.class
	)
)
@Filter(
	name="activeAccount",
	condition="{a}.active = :active and {ad}.deleted = false",
	aliases = {
		@SqlFragmentAlias(alias = "a", table= "account"),
		@SqlFragmentAlias(alias = "ad", table= "account_details"),
	}
)
public static class Account {

	@Id
	private Long id;

	private Double amount;

	private Double rate;

	private boolean active;

	@Column(table = "account_details")
	private boolean deleted;

	//Getters and setters omitted for brevity

}

Now, when fetching the Account entities and activating the filter, Hibernate is going to apply the right table aliases to the filter predicates:

Example 386. Fetching a collection filtered with @SqlFragmentAlias
entityManager
	.unwrap(Session.class)
	.enableFilter("activeAccount")
	.setParameter("active", true);

List<Account> accounts = entityManager.createQuery(
	"select a from Account a", Account.class)
.getResultList();
select
    filtersqlf0_.id as id1_0_,
    filtersqlf0_.active as active2_0_,
    filtersqlf0_.amount as amount3_0_,
    filtersqlf0_.rate as rate4_0_,
    filtersqlf0_1_.deleted as deleted1_1_
from
    account filtersqlf0_
left outer join
    account_details filtersqlf0_1_
        on filtersqlf0_.id=filtersqlf0_1_.id
where
    filtersqlf0_.active = ?
    and filtersqlf0_1_.deleted = false

-- binding parameter [1] as [BOOLEAN] - [true]

6.9.5. @FilterJoinTable

When using the @Filter annotation with collections, the filtering is done against the child entries (entities or embeddables). However, if you have a link table between the parent entity and the child table, then you need to use the @FilterJoinTable to filter child entries according to some column contained in the join table.

The @FilterJoinTable annotation can be, therefore, applied to a unidirectional @OneToMany collection as illustrated in the following mapping:

Example 387. @FilterJoinTable mapping usage
 @Entity(name = "Client")
 @FilterDef(
     name="firstAccounts",
     parameters=@ParamDef(
         name="maxOrderId",
         type=int.class
    )
)
 public static class Client {

     @Id
     private Long id;

     private String name;

     @OneToMany(cascade = CascadeType.ALL)
     @OrderColumn(name = "order_id")
     @FilterJoinTable(
         name="firstAccounts",
         condition="order_id <= :maxOrderId"
    )
     private List<Account> accounts = new ArrayList<>();

     //Getters and setters omitted for brevity

     public void addAccount(Account account) {
         this.accounts.add(account);
     }
 }

 @Entity(name = "Account")
 public static class Account {

     @Id
     private Long id;

     @Column(name = "account_type")
     @Enumerated(EnumType.STRING)
     private AccountType type;

     private Double amount;

     private Double rate;

     //Getters and setters omitted for brevity
 }

The firstAccounts filter will allow us to get only the Account entities that have the order_id (which tells the position of every entry inside the accounts collection) less than a given number (e.g. maxOrderId).

Let’s assume our database contains the following entities:

Example 388. Persisting and fetching entities with a @FilterJoinTable mapping
 Client client = new Client()
 .setId(1L)
 .setName("John Doe");

 client.addAccount(
     new Account()
     .setId(1L)
     .setType(AccountType.CREDIT)
     .setAmount(5000d)
     .setRate(1.25 / 100)
);

 client.addAccount(
     new Account()
     .setId(2L)
     .setType(AccountType.DEBIT)
     .setAmount(0d)
     .setRate(1.05 / 100)
);

 client.addAccount(
     new Account()
     .setType(AccountType.DEBIT)
     .setId(3L)
     .setAmount(250d)
     .setRate(1.05 / 100)
);

 entityManager.persist(client);
INSERT INTO Client (name, id)
VALUES ('John Doe', 1)

INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (5000.0, 1, 0.0125, 'CREDIT', 1)

INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (0.0, 1, 0.0105, 'DEBIT', 2)

INSERT INTO Account (amount, client_id, rate, account_type, id)
VALUES (250.0, 1, 0.0105, 'DEBIT', 3)

INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 0, 1)

INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 0, 1)

INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 1, 2)

INSERT INTO Client_Account (Client_id, order_id, accounts_id)
VALUES (1, 2, 3)

The collections can be filtered only if the associated filter is enabled on the currently running Hibernate Session.

Example 389. Traversing collections mapped with @FilterJoinTable without enabling the filter
Client client = entityManager.find(Client.class, 1L);

assertEquals(3, client.getAccounts().size());
SELECT
    ca.Client_id as Client_i1_2_0_,
    ca.accounts_id as accounts2_2_0_,
    ca.order_id as order_id3_0_,
    a.id as id1_0_1_,
    a.amount as amount3_0_1_,
    a.rate as rate4_0_1_,
    a.account_type as account_5_0_1_
FROM
    Client_Account ca
INNER JOIN
    Account a
ON  ca.accounts_id=a.id
WHERE
    ca.Client_id = ?

-- binding parameter [1] as [BIGINT] - [1]

If we enable the filter and set the maxOrderId to 1 when fetching the accounts collections, Hibernate is going to apply the @FilterJoinTable clause filtering criteria, and we will get just 2 Account entities, with the order_id values of 0 and 1.

Example 390. Traversing collections mapped with @FilterJoinTable
Client client = entityManager.find(Client.class, 1L);

entityManager
    .unwrap(Session.class)
    .enableFilter("firstAccounts")
    .setParameter("maxOrderId", 1);

assertEquals(2, client.getAccounts().size());
SELECT
    ca.Client_id as Client_i1_2_0_,
    ca.accounts_id as accounts2_2_0_,
    ca.order_id as order_id3_0_,
    a.id as id1_0_1_,
    a.amount as amount3_0_1_,
    a.rate as rate4_0_1_,
    a.account_type as account_5_0_1_
FROM
    Client_Account ca
INNER JOIN
    Account a
ON  ca.accounts_id=a.id
WHERE
    ca.order_id <= ?
    AND ca.Client_id = ?

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [BIGINT] - [1]

6.10. Modifying managed/persistent state

Entities in managed/persistent state may be manipulated by the application, and any changes will be automatically detected and persisted when the persistence context is flushed. There is no need to call a particular method to make your modifications persistent.

Example 391. Modifying managed state with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
person.setName("John Doe");
entityManager.flush();
Example 392. Modifying managed state with Hibernate API
Person person = session.byId(Person.class).load(personId);
person.setName("John Doe");
session.flush();

By default, when you modify an entity, all columns but the identifier are being set during update.

Therefore, considering you have the following Product entity mapping:

Example 393. Product entity mapping
@Entity(name = "Product")
public static class Product {

	@Id
	private Long id;

	@Column
	private String name;

	@Column
	private String description;

	@Column(name = "price_cents")
	private Integer priceCents;

	@Column
	private Integer quantity;

	//Getters and setters are omitted for brevity

}

If you persist the following Product entity:

Example 394. Persisting a Product entity
Product book = new Product();
book.setId(1L);
book.setName("High-Performance Java Persistence");
book.setDescription("Get the most out of your persistence layer");
book.setPriceCents(29_99);
book.setQuantity(10_000);

entityManager.persist(book);

When you modify the Product entity, Hibernate generates the following SQL UPDATE statement:

Example 395. Modifying the Product entity
doInJPA(this::entityManagerFactory, entityManager -> {
	Product book = entityManager.find(Product.class, 1L);
	book.setPriceCents(24_99);
});
UPDATE
    Product
SET
    description = ?,
    name = ?,
    price_cents = ?,
    quantity = ?
WHERE
    id = ?

-- binding parameter [1] as [VARCHAR] - [Get the most out of your persistence layer]
-- binding parameter [2] as [VARCHAR] - [High-Performance Java Persistence]
-- binding parameter [3] as [INTEGER] - [2499]
-- binding parameter [4] as [INTEGER] - [10000]
-- binding parameter [5] as [BIGINT]  - [1]

The default UPDATE statement containing all columns has two advantages:

  • it allows you to better benefit from JDBC Statement caching.

  • it allows you to enable batch updates even if multiple entities modify different properties.

However, there is also one downside to including all columns in the SQL UPDATE statement. If you have multiple indexes, the database might update those redundantly even if you don’t actually modify all column values.

To fix this issue, you can use dynamic updates.

6.10.1. Dynamic updates

To enable dynamic updates, you need to annotate the entity with the @DynamicUpdate annotation:

Example 396. Product entity mapping
@Entity(name = "Product")
@DynamicUpdate
public static class Product {

	@Id
	private Long id;

	@Column
	private String name;

	@Column
	private String description;

	@Column(name = "price_cents")
	private Integer priceCents;

	@Column
	private Integer quantity;

	//Getters and setters are omitted for brevity

}

This time, when rerunning the previous test case, Hibernate generates the following SQL UPDATE statement:

Example 397. Modifying the Product entity with a dynamic update
UPDATE
    Product
SET
    price_cents = ?
WHERE
    id = ?

-- binding parameter [1] as [INTEGER] - [2499]
-- binding parameter [2] as [BIGINT]  - [1]

The dynamic update allows you to set just the columns that were modified in the associated entity.

6.11. Refresh entity state

You can reload an entity instance and its collections at any time.

Example 398. Refreshing entity state with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);

entityManager.createQuery("update Person set name = UPPER(name)").executeUpdate();

entityManager.refresh(person);
assertEquals("JOHN DOE", person.getName());
Example 399. Refreshing entity state with Hibernate API
Person person = session.byId(Person.class).load(personId);

session.doWork(connection -> {
	try(Statement statement = connection.createStatement()) {
		statement.executeUpdate("UPDATE Person SET name = UPPER(name)");
	}
});

session.refresh(person);
assertEquals("JOHN DOE", person.getName());

One case where this is useful is when it is known that the database state has changed since the data was read. Refreshing allows the current database state to be pulled into the entity instance and the persistence context.

Another case where this might be useful is when database triggers are used to initialize some of the properties of the entity.

Only the entity instance and its value type collections are refreshed unless you specify REFRESH as a cascade style of any associations. However, please note that Hibernate has the capability to handle this automatically through its notion of generated properties. See the discussion of non-identifier generated attributes.

Traditionally, Hibernate allowed detached entities to be refreshed. Unfortunately, Jakarta Persistence prohibits this practice and specifies that an IllegalArgumentException should be thrown instead.

For this reason, when bootstrapping the Hibernate SessionFactory using the native API, the legacy detached entity refresh behavior is going to be preserved. On the other hand, when bootstrapping Hibernate through the Jakarta Persistence EntityManagerFactory building process, detached entities are not allowed to be refreshed by default.

However, this default behavior can be overwritten through the hibernate.allow_refresh_detached_entity configuration property. If this property is explicitly set to true, then you can refresh detached entities even when using the Jakarta Persistence bootstraps mechanism, therefore bypassing the Jakarta Persistence specification restriction.

For more about the hibernate.allow_refresh_detached_entity configuration property, check out the Configurations section as well.

6.11.1. Refresh gotchas

The refresh entity state transition is meant to overwrite the entity attributes according to the info currently contained in the associated database record.

However, you have to be very careful when cascading the refresh action to any transient entity.

For instance, consider the following example:

Example 400. Refreshing entity state gotcha
try {
	Person person = entityManager.find(Person.class, personId);

	Book book = new Book();
	book.setId(100L);
	book.setTitle("Hibernate User Guide");
	book.setAuthor(person);
	person.getBooks().add(book);

	entityManager.refresh(person);
}
catch (EntityNotFoundException expected) {
	log.info("Beware when cascading the refresh associations to transient entities!");
}

In the aforementioned example, an EntityNotFoundException is thrown because the Book entity is still in a transient state. When the refresh action is cascaded from the Person entity, Hibernate will not be able to locate the Book entity in the database.

For this reason, you should be very careful when mixing the refresh action with transient child entity objects.

6.12. Working with detached data

Detachment is the process of working with data outside the scope of any persistence context. Data becomes detached in a number of ways. Once the persistence context is closed, all data that was associated with it becomes detached. Clearing the persistence context has the same effect. Evicting a particular entity from the persistence context makes it detached. And finally, serialization will make the deserialized form be detached (the original instance is still managed).

Detached data can still be manipulated, however, the persistence context will no longer automatically know about these modifications, and the application will need to intervene to make the changes persistent again.

6.12.1. Reattaching detached data

Reattachment is the process of taking an incoming entity instance that is in the detached state and re-associating it with the current persistence context.

Jakarta Persistence does not support reattaching detached data. This is only available through Hibernate org.hibernate.Session.

Example 401. Reattaching a detached entity using lock
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");

session.lock(person, LockMode.NONE);
Example 402. Reattaching a detached entity using saveOrUpdate
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");

session.merge(person);

The method name update is a bit misleading here. It does not mean that an SQL UPDATE is immediately performed. It does, however, mean that an SQL UPDATE will be performed when the persistence context is flushed since Hibernate does not know its previous state against which to compare for changes. If the entity is mapped with select-before-update, Hibernate will pull the current state from the database and see if an update is needed.

Provided the entity is detached, update and saveOrUpdate operate exactly the same.

6.12.2. Merging detached data

Merging is the process of taking an incoming entity instance that is in the detached state and copying its data over onto a new managed instance.

Although not exactly per se, the following example is a good visualization of the merge operation internals.

Example 403. Visualizing merge
public Person merge(Person detached) {
	Person newReference = session.byId(Person.class).load(detached.getId());
	newReference.setName(detached.getName());
	return newReference;
}
Example 404. Merging a detached entity with Jakarta Persistence
Person person = entityManager.find(Person.class, personId);
//Clear the EntityManager so the person entity becomes detached
entityManager.clear();
person.setName("Mr. John Doe");

person = entityManager.merge(person);
Example 405. Merging a detached entity with Hibernate API
Person person = session.byId(Person.class).load(personId);
//Clear the Session so the person entity becomes detached
session.clear();
person.setName("Mr. John Doe");

person = (Person) session.merge(person);
Merging gotchas

For example, Hibernate throws IllegalStateException when merging a parent entity which has references to 2 detached child entities child1 and child2 (obtained from different sessions), and child1 and child2 represent the same persistent entity, Child.

A new configuration property, hibernate.event.merge.entity_copy_observer, controls how Hibernate will respond when multiple representations of the same persistent entity ("entity copy") is detected while merging.

The possible values are:

disallow (the default)

throws IllegalStateException if an entity copy is detected

allow

performs the merge operation on each entity copy that is detected

log

(provided for testing only) performs the merge operation on each entity copy that is detected and logs information about the entity copies. This setting requires DEBUG logging be enabled for org.hibernate.event.internal.EntityCopyAllowedLoggedObserver

In addition, the application may customize the behavior by providing an implementation of org.hibernate.event.spi.EntityCopyObserver and setting hibernate.event.merge.entity_copy_observer to the class name. When this property is set to allow or log, Hibernate will merge each entity copy detected while cascading the merge operation. In the process of merging each entity copy, Hibernate will cascade the merge operation from each entity copy to its associations with cascade=CascadeType.MERGE or CascadeType.ALL. The entity state resulting from merging an entity copy will be overwritten when another entity copy is merged.

Because cascade order is undefined, the order in which the entity copies are merged is undefined. As a result, if property values in the entity copies are not consistent, the resulting entity state will be indeterminate, and data will be lost from all entity copies except for the last one merged. Therefore, the last writer wins.

If an entity copy cascades the merge operation to an association that is (or contains) a new entity, that new entity will be merged (i.e., persisted and the merge operation will be cascaded to its associations according to its mapping), even if that same association is ultimately overwritten when Hibernate merges a different representation having a different value for its association.

If the association is mapped with orphanRemoval = true, the new entity will not be deleted because the semantics of orphanRemoval do not apply if the entity being orphaned is a new entity.

There are known issues when representations of the same persistent entity have different values for a collection. See HHH-9239 and HHH-9240 for more details. These issues can cause data loss or corruption.

By setting hibernate.event.merge.entity_copy_observer configuration property to allow or log, Hibernate will allow entity copies of any type of entity to be merged.

The only way to exclude particular entity classes or associations that contain critical data is to provide a custom implementation of org.hibernate.event.spi.EntityCopyObserver with the desired behavior, and setting hibernate.event.merge.entity_copy_observer to the class name.

Hibernate provides limited DEBUG logging capabilities that can help determine the entity classes for which entity copies were found. By setting hibernate.event.merge.entity_copy_observer to log and enabling DEBUG logging for org.hibernate.event.internal.EntityCopyAllowedLoggedObserver, the following will be logged each time an application calls EntityManager.merge( entity ) or
Session.merge( entity ):

  • number of times multiple representations of the same persistent entity was detected summarized by entity name;

  • details by entity name and ID, including output from calling toString() on each representation being merged as well as the merge result.

The log should be reviewed to determine if multiple representations of entities containing critical data are detected. If so, the application should be modified so there is only one representation, and a custom implementation of org.hibernate.event.spi.EntityCopyObserver should be provided to disallow entity copies for entities with critical data.

Using optimistic locking is recommended to detect if different representations are from different versions of the same persistent entity. If they are not from the same version, Hibernate will throw either the Jakarta Persistence OptimisticEntityLockException or the native StaleObjectStateException depending on your bootstrapping strategy.

6.13. Checking persistent state

An application can verify the state of entities and collections in relation to the persistence context.

Example 406. Verifying managed state with Jakarta Persistence
boolean contained = entityManager.contains(person);
Example 407. Verifying managed state with Hibernate API
boolean contained = session.contains(person);
Example 408. Verifying laziness with Jakarta Persistence
PersistenceUnitUtil persistenceUnitUtil = entityManager.getEntityManagerFactory().getPersistenceUnitUtil();

boolean personInitialized = persistenceUnitUtil.isLoaded(person);

boolean personBooksInitialized = persistenceUnitUtil.isLoaded(person.getBooks());

boolean personNameInitialized = persistenceUnitUtil.isLoaded(person, "name");
Example 409. Verifying laziness with Hibernate API
boolean personInitialized = Hibernate.isInitialized(person);

boolean personBooksInitialized = Hibernate.isInitialized(person.getBooks());

boolean personNameInitialized = Hibernate.isPropertyInitialized(person, "name");

In Jakarta Persistence there is an alternative means to check laziness using the following jakarta.persistence.PersistenceUtil pattern (which is recommended wherever possible).

Example 410. Alternative Jakarta Persistence means to verify laziness
PersistenceUtil persistenceUnitUtil = Persistence.getPersistenceUtil();

boolean personInitialized = persistenceUnitUtil.isLoaded(person);

boolean personBooksInitialized = persistenceUnitUtil.isLoaded(person.getBooks());

boolean personNameInitialized = persistenceUnitUtil.isLoaded(person, "name");

6.14. Evicting entities

When the flush() method is called, the state of the entity is synchronized with the database. If you do not want this synchronization to occur, or if you are processing a huge number of objects and need to manage memory efficiently, the evict() method can be used to remove the object and its collections from the first-level cache.

Example 411. Detaching an entity from the EntityManager
for(Person person : entityManager.createQuery("select p from Person p", Person.class)
		.getResultList()) {
	dtos.add(toDTO(person));
	entityManager.detach(person);
}
Example 412. Evicting an entity from the Hibernate Session
Session session = entityManager.unwrap(Session.class);
for(Person person : (List<Person>) session.createSelectionQuery("select p from Person p").list()) {
	dtos.add(toDTO(person));
	session.evict(person);
}

To detach all entities from the current persistence context, both the EntityManager and the Hibernate Session define a clear() method.

Example 413. Clearing the persistence context
entityManager.clear();

session.clear();

To verify if an entity instance is currently attached to the running persistence context, both the EntityManager and the Hibernate Session define a contains(Object entity) method.

Example 414. Verify if an entity is contained in a persistence context
entityManager.contains(person);

session.contains(person);

6.15. Cascading entity state transitions

Jakarta Persistence allows you to propagate the state transition from a parent entity to a child. For this purpose, the Jakarta Persistence jakarta.persistence.CascadeType defines various cascade types:

ALL

cascades all entity state transitions.

PERSIST

cascades the entity persist operation.

MERGE

cascades the entity merge operation.

REMOVE

cascades the entity remove operation.

REFRESH

cascades the entity refresh operation.

DETACH

cascades the entity detach operation.

Additionally, the CascadeType.ALL will propagate any Hibernate-specific operation, which is defined by the org.hibernate.annotations.CascadeType enum:

SAVE_UPDATE

cascades the entity saveOrUpdate operation.

REPLICATE

cascades the entity replicate operation.

LOCK

cascades the entity lock operation.

The following examples will explain some of the aforementioned cascade operations using the following entities:

@Entity
public class Person {

    @Id
    private Long id;

    private String name;

    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
    private List<Phone> phones = new ArrayList<>();

    //Getters and setters are omitted for brevity

    public void addPhone(Phone phone) {
        this.phones.add(phone);
        phone.setOwner(this);
    }
}


@Entity
public class Phone {

    @Id
    private Long id;

    @Column(name = "`number`")
    private String number;

    @ManyToOne(fetch = FetchType.LAZY)
    private Person owner;

    //Getters and setters are omitted for brevity
}

6.15.1. CascadeType.PERSIST

The CascadeType.PERSIST allows us to persist a child entity along with the parent one.

Example 415. CascadeType.PERSIST example
Person person = new Person();
person.setId(1L);
person.setName("John Doe");

Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("123-456-7890");

person.addPhone(phone);

entityManager.persist(person);
INSERT INTO Person ( name, id )
VALUES ( 'John Doe', 1 )

INSERT INTO Phone ( `number`, person_id, id )
VALUE ( '123-456-7890', 1, 1 )

Even if just the Person parent entity was persisted, Hibernate has managed to cascade the persist operation to the associated Phone child entity as well.

6.15.2. CascadeType.MERGE

The CascadeType.MERGE allows us to merge a child entity along with the parent one.

Example 416. CascadeType.MERGE example
Phone phone = entityManager.find(Phone.class, 1L);
Person person = phone.getOwner();

person.setName("John Doe Jr.");
phone.setNumber("987-654-3210");

entityManager.clear();

entityManager.merge(person);
SELECT
    p.id as id1_0_1_,
    p.name as name2_0_1_,
    ph.owner_id as owner_id3_1_3_,
    ph.id as id1_1_3_,
    ph.id as id1_1_0_,
    ph."number" as number2_1_0_,
    ph.owner_id as owner_id3_1_0_
FROM
    Person p
LEFT OUTER JOIN
    Phone ph
        on p.id=ph.owner_id
WHERE
    p.id = 1

During merge, the current state of the entity is copied onto the entity version that was just fetched from the database. That’s the reason why Hibernate executed the SELECT statement which fetched both the Person entity along with its children.

6.15.3. CascadeType.REMOVE

The CascadeType.REMOVE allows us to remove a child entity along with the parent one. Traditionally, Hibernate called this operation delete, that’s why the org.hibernate.annotations.CascadeType provides a DELETE cascade option. However, CascadeType.REMOVE and org.hibernate.annotations.CascadeType.DELETE are identical.

Example 417. CascadeType.REMOVE example
Person person = entityManager.find(Person.class, 1L);

entityManager.remove(person);
DELETE FROM Phone WHERE id = 1

DELETE FROM Person WHERE id = 1

6.15.4. CascadeType.DETACH

CascadeType.DETACH is used to propagate the detach operation from a parent entity to a child.

Example 418. CascadeType.DETACH example
Person person = entityManager.find(Person.class, 1L);
assertEquals(1, person.getPhones().size());
Phone phone = person.getPhones().get(0);

assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));

entityManager.detach(person);

assertFalse(entityManager.contains(person));
assertFalse(entityManager.contains(phone));

6.15.5. CascadeType.LOCK

Although unintuitively, CascadeType.LOCK does not propagate a lock request from a parent entity to its children. Such a use case requires the use of the PessimisticLockScope.EXTENDED value of the jakarta.persistence.lock.scope property.

However, CascadeType.LOCK allows us to reattach a parent entity along with its children to the currently running Persistence Context.

Example 419. CascadeType.LOCK example
Person person = entityManager.find(Person.class, 1L);
assertEquals(1, person.getPhones().size());
Phone phone = person.getPhones().get(0);

assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));

entityManager.detach(person);

assertFalse(entityManager.contains(person));
assertFalse(entityManager.contains(phone));

entityManager.unwrap(Session.class)
		.lock(person, new LockOptions(LockMode.NONE));

assertTrue(entityManager.contains(person));
assertTrue(entityManager.contains(phone));

6.15.6. CascadeType.REFRESH

The CascadeType.REFRESH is used to propagate the refresh operation from a parent entity to a child. The refresh operation will discard the current entity state, and it will override it using the one loaded from the database.

Example 420. CascadeType.REFRESH example
Person person = entityManager.find(Person.class, 1L);
Phone phone = person.getPhones().get(0);

person.setName("John Doe Jr.");
phone.setNumber("987-654-3210");

entityManager.refresh(person);

assertEquals("John Doe", person.getName());
assertEquals("123-456-7890", phone.getNumber());
SELECT
    p.id as id1_0_1_,
    p.name as name2_0_1_,
    ph.owner_id as owner_id3_1_3_,
    ph.id as id1_1_3_,
    ph.id as id1_1_0_,
    ph."number" as number2_1_0_,
    ph.owner_id as owner_id3_1_0_
FROM
    Person p
LEFT OUTER JOIN
    Phone ph
        ON p.id=ph.owner_id
WHERE
    p.id = 1

In the aforementioned example, you can see that both the Person and Phone entities are refreshed even if we only called this operation on the parent entity only.

6.15.7. CascadeType.REPLICATE

The CascadeType.REPLICATE is to replicate both the parent and the child entities. The replicate operation allows you to synchronize entities coming from different sources of data.

Example 421. CascadeType.REPLICATE example
Person person = new Person();
person.setId(1L);
person.setName("John Doe Sr.");

Phone phone = new Phone();
phone.setId(1L);
phone.setNumber("(01) 123-456-7890");
person.addPhone(phone);

entityManager.unwrap(Session.class).replicate(person, ReplicationMode.OVERWRITE);
SELECT
    id
FROM
    Person
WHERE
    id = 1

SELECT
    id
FROM
    Phone
WHERE
    id = 1

UPDATE
    Person
SET
    name = 'John Doe Sr.'
WHERE
    id = 1

UPDATE
    Phone
SET
    "number" = '(01) 123-456-7890',
    owner_id = 1
WHERE
    id = 1

As illustrated by the SQL statements being generated, both the Person and Phone entities are replicated to the underlying database rows.

6.15.8. @OnDelete cascade

While the previous cascade types propagate entity state transitions, the @OnDelete cascade is a DDL-level FK feature which allows you to remove a child record whenever the parent row is deleted.

So, when annotating the @ManyToOne association with @OnDelete( action = OnDeleteAction.CASCADE ), the automatic schema generator will apply the ON DELETE CASCADE SQL directive to the Foreign Key declaration, as illustrated by the following example.

Example 422. @OnDelete @ManyToOne mapping
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	//Getters and setters are omitted for brevity

}
@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	@Column(name = "`number`")
	private String number;

	@ManyToOne(fetch = LAZY)
	@OnDelete(action = CASCADE)
	private Person owner;

	//Getters and setters are omitted for brevity

}
create table Person (
    id bigint not null,
    name varchar(255),
    primary key (id)
)

create table Phone (
    id bigint not null,
    "number" varchar(255),
    owner_id bigint,
    primary key (id)
)

alter table Phone
    add constraint FK82m836qc1ss2niru7eogfndhl
    foreign key (owner_id)
    references Person
    on delete cascade

Now, you can just remove the Person entity, and the associated Phone entities are going to be deleted automatically via the Foreign Key cascade.

Example 423. @OnDelete @ManyToOne delete example
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
delete from Person where id = ?

-- binding parameter [1] as [BIGINT] - [1]

The @OnDelete annotation can also be placed on a collection, as illustrated in the following example.

Example 424. @OnDelete @OneToMany mapping
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String name;

	@OneToMany(mappedBy = "owner", cascade = CascadeType.ALL)
	@OnDelete(action = OnDeleteAction.CASCADE)
	private List<Phone> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}
@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	@Column(name = "`number`")
	private String number;

	@ManyToOne(fetch = FetchType.LAZY)
	private Person owner;

	//Getters and setters are omitted for brevity

}

Now, when removing the Person entity, all the associated Phone child entities are deleted via the Foreign Key cascade even if the @OneToMany collection was using the CascadeType.ALL attribute.

Example 425. @OnDelete @ManyToOne delete example
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);
delete from Person where id = ?

-- binding parameter [1] as [BIGINT] - [1]

Without the @OnDelete annotation, the @OneToMany association relies on the cascade attribute to propagate the remove entity state transition from the parent entity to its children. However, when the @OnDelete annotation is in place, Hibernate prevents the child entity DELETE statement from being executed while flushing the Persistence Context.

This way, only the parent entity gets deleted, and all the associated child records are removed by the database engine, instead of being deleted explicitly via DELETE statements.

6.16. Exception handling

If the Jakarta Persistence EntityManager or the Hibernate-specific Session throws an exception, including any JDBC SQLException, you have to immediately rollback the database transaction and close the current EntityManager or Session.

Certain methods of the Jakarta Persistence EntityManager or the Hibernate Session will not leave the Persistence Context in a consistent state. As a rule of thumb, no exception thrown by Hibernate can be treated as recoverable. Ensure that the Session will be closed by calling the close() method in a finally block.

Rolling back the database transaction does not put your business objects back into the state they were at the start of the transaction. This means that the database state and the business objects will be out of sync. Usually, this is not a problem because exceptions are not recoverable and you will have to start over after rollback anyway.

The Jakarta Persistence PersistenceException or the HibernateException wraps most of the errors that can occur in a Hibernate persistence layer.

Both the PersistenceException and the HibernateException are runtime exceptions because, in our opinion, we should not force the application developer to catch an unrecoverable exception at a low layer. In most systems, unchecked and fatal exceptions are handled in one of the first frames of the method call stack (i.e., in higher layers) and either an error message is presented to the application user or some other appropriate action is taken. Note that Hibernate might also throw other unchecked exceptions that are not a HibernateException. These are not recoverable either, and appropriate action should be taken.

Hibernate wraps the JDBC SQLException, thrown while interacting with the database, in a JDBCException. In fact, Hibernate will attempt to convert the exception into a more meaningful subclass of JDBCException. The underlying SQLException is always available via JDBCException.getSQLException(). Hibernate converts the SQLException into an appropriate JDBCException subclass using the SQLExceptionConverter attached to the current SessionFactory.

By default, the SQLExceptionConverter is defined by the configured Hibernate Dialect via the buildSQLExceptionConversionDelegate method which is overridden by several database-specific Dialects.

The standard JDBCException subtypes are:

ConstraintViolationException

indicates some form of integrity constraint violation.

DataException

indicates that evaluation of the valid SQL statement against the given data resulted in some illegal operation, mismatched types, truncation or incorrect cardinality.

GenericJDBCException

a generic exception which did not fall into any of the other categories.

JDBCConnectionException

indicates an error with the underlying JDBC communication.

LockAcquisitionException

indicates an error acquiring a lock level necessary to perform the requested operation.

LockTimeoutException

indicates that the lock acquisition request has timed out.

PessimisticLockException

indicates that a lock acquisition request has failed.

QueryTimeoutException

indicates that the current executing query has timed out.

SQLGrammarException

indicates a grammar or syntax problem with the issued SQL.

Starting with Hibernate 5.2, the Hibernate Session extends the Jakarta Persistence EntityManager. For this reason, when a SessionFactory is built via Hibernate’s native bootstrapping, the HibernateException or SQLException can be wrapped in a Jakarta Persistence PersistenceException when thrown by Session methods that implement EntityManager methods (e.g., Session.merge(Object object), Session.flush()).

If your SessionFactory is built via Hibernate’s native bootstrapping, and you don’t want the Hibernate exceptions to be wrapped in the Jakarta Persistence PersistenceException, you need to set the hibernate.native_exception_handling_51_compliance configuration property to true. See the hibernate.native_exception_handling_51_compliance configuration property for more details.

7. Flushing

Flushing is the process of synchronizing the state of the persistence context with the underlying database. The EntityManager and the Hibernate Session expose a set of methods, through which the application developer can change the persistent state of an entity.

The persistence context acts as a transactional write-behind cache, queuing any entity state change. Like any write-behind cache, changes are first applied in-memory and synchronized with the database during the flush time. The flush operation takes every entity state change and translates it to an INSERT, UPDATE or DELETE statement.

Because DML statements are grouped together, Hibernate can apply batching transparently. See the Batching chapter for more information.

The flushing strategy is given by the flushMode of the current running Hibernate Session. Although Jakarta Persistence defines only two flushing strategies (AUTO and COMMIT), Hibernate has a much broader spectrum of flush types:

ALWAYS

Flushes the Session before every query.

AUTO

This is the default mode, and it flushes the Session only if necessary.

COMMIT

The Session tries to delay the flush until the current Transaction is committed, although it might flush prematurely too.

MANUAL

The Session flushing is delegated to the application, which must call Session.flush() explicitly in order to apply the persistence context changes.

7.1. AUTO flush

By default, Hibernate uses the AUTO flush mode which triggers a flush in the following circumstances:

  • prior to committing a Transaction

  • prior to executing a JPQL/HQL query that overlaps with the queued entity actions

  • before executing any native SQL query that has no registered synchronization

7.1.1. AUTO flush on commit

In the following example, an entity is persisted, and then the transaction is committed.

Example 426. Automatic flushing on commit
entityManager = entityManagerFactory().createEntityManager();
txn = entityManager.getTransaction();
txn.begin();

Person person = new Person("John Doe");
entityManager.persist(person);
log.info("Entity is in persisted state");

txn.commit();
--INFO: Entity is in persisted state
INSERT INTO Person (name, id) VALUES ('John Doe', 1)

Hibernate logs the message prior to inserting the entity because the flush only occurred during transaction commit.

This is valid for the SEQUENCE and TABLE identifier generators. The IDENTITY generator must execute the insert right after calling persist(). For more details, see the discussion of generators in Identifier generators.

7.1.2. AUTO flush on JPQL/HQL query

A flush may also be triggered when executing an entity query.

Example 427. Automatic flushing on JPQL/HQL
Person person = new Person("John Doe");
entityManager.persist(person);
entityManager.createQuery("select p from Advertisement p").getResultList();
entityManager.createQuery("select p from Person p").getResultList();
SELECT a.id AS id1_0_ ,
       a.title AS title2_0_
FROM   Advertisement a

INSERT INTO Person (name, id) VALUES ('John Doe', 1)

SELECT p.id AS id1_1_ ,
       p.name AS name2_1_
FROM   Person p

The reason why the Advertisement entity query didn’t trigger a flush is that there’s no overlapping between the Advertisement and the Person tables:

Example 428. Automatic flushing on JPQL/HQL entities
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	//Getters and setters are omitted for brevity

}

@Entity(name = "Advertisement")
public static class Advertisement {

	@Id
	@GeneratedValue
	private Long id;

	private String title;

	//Getters and setters are omitted for brevity

}

When querying for a Person entity, the flush is triggered prior to executing the entity query.

Example 429. Automatic flushing on JPQL/HQL
Person person = new Person("John Doe");
entityManager.persist(person);
entityManager.createQuery("select p from Person p").getResultList();
INSERT INTO Person (name, id) VALUES ('John Doe', 1)

SELECT p.id AS id1_1_ ,
       p.name AS name2_1_
FROM   Person p

This time, the flush was triggered by a JPQL query because the pending entity persisting action overlaps with the query being executed.

7.1.3. AUTO flush on native SQL query

When executing a native SQL query, a flush is always triggered when using the EntityManager API.

Example 430. Automatic flushing on native SQL using EntityManager
assertTrue(((Number) entityManager
		.createNativeQuery("select count(*) from Person")
		.getSingleResult()).intValue() == 0);

Person person = new Person("John Doe");
entityManager.persist(person);

assertTrue(((Number) entityManager
		.createNativeQuery("select count(*) from Person")
		.getSingleResult()).intValue() == 1);

If you bootstrap Hibernate natively, and not through Jakarta Persistence, by default, the Session API will trigger a flush automatically when executing a native query.

Example 431. Automatic flushing on native SQL using Session
assertTrue(((Number) session
		.createNativeQuery("select count(*) from Person", Integer.class)
		.getSingleResult()).intValue() == 0);

Person person = new Person("John Doe");
session.persist(person);

assertTrue(((Number) session
		.createNativeQuery("select count(*) from Person", Integer.class)
		.uniqueResult()).intValue() == 0);

To flush the Session, the query must use a synchronization:

Example 432. Automatic flushing on native SQL with Session synchronization
assertTrue(((Number) entityManager
		.createNativeQuery("select count(*) from Person")
		.getSingleResult()).intValue() == 0);

Person person = new Person("John Doe");
entityManager.persist(person);
Session session = entityManager.unwrap(Session.class);

assertTrue(((Number) session
		.createNativeQuery("select count(*) from Person", Integer.class)
		.addSynchronizedEntityClass(Person.class)
		.uniqueResult()).intValue() == 1);

7.2. COMMIT flush

Jakarta Persistence also defines a COMMIT flush mode, which is described as follows:

If FlushModeType.COMMIT is set, the effect of updates made to entities in the persistence context upon queries is unspecified.

— Section 3.10.8 of the Java Persistence 2.1 Specification

When executing a JPQL query, the persistence context is only flushed when the current running transaction is committed.

Example 433. COMMIT flushing on JPQL
Person person = new Person("John Doe");
entityManager.persist(person);

entityManager.createQuery("select p from Advertisement p")
    .setFlushMode(FlushModeType.COMMIT)
    .getResultList();

entityManager.createQuery("select p from Person p")
    .setFlushMode(FlushModeType.COMMIT)
    .getResultList();
SELECT a.id AS id1_0_ ,
       a.title AS title2_0_
FROM   Advertisement a

SELECT p.id AS id1_1_ ,
       p.name AS name2_1_
FROM   Person p

INSERT INTO Person (name, id) VALUES ('John Doe', 1)

Because the Jakarta Persistence doesn’t impose a strict rule on delaying flushing, when executing a native SQL query, the persistence context is going to be flushed.

Example 434. COMMIT flushing on native SQL
Person person = new Person("John Doe");
entityManager.persist(person);

assertTrue(((Number) entityManager
    .createNativeQuery("select count(*) from Person")
    .getSingleResult()).intValue() == 1);
INSERT INTO Person (name, id) VALUES ('John Doe', 1)

SELECT COUNT(*) FROM Person

7.3. ALWAYS flush

The ALWAYS is only available with the native Session API.

The ALWAYS flush mode triggers a persistence context flush even when executing a native SQL query against the Session API.

Example 435. COMMIT flushing on native SQL
Person person = new Person("John Doe");
entityManager.persist(person);

Session session = entityManager.unwrap(Session.class);
assertTrue(((Number) session
        .createNativeQuery("select count(*) from Person", Integer.class)
        .setHibernateFlushMode(FlushMode.ALWAYS)
        .uniqueResult()).intValue() == 1);
INSERT INTO Person (name, id) VALUES ('John Doe', 1)

SELECT COUNT(*) FROM Person

7.4. MANUAL flush

Both the EntityManager and the Hibernate Session define a flush() method that, when called, triggers a manual flush. Hibernate also provides a MANUAL flush mode so the persistence context can only be flushed manually.

Example 436. MANUAL flushing
Person person = new Person("John Doe");
entityManager.persist(person);

Session session = entityManager.unwrap(Session.class);
session.setHibernateFlushMode(FlushMode.MANUAL);

assertTrue(((Number) entityManager
    .createQuery("select count(id) from Person")
    .getSingleResult()).intValue() == 0);

assertTrue(((Number) session
    .createNativeQuery("select count(*) from Person", Integer.class)
    .uniqueResult()).intValue() == 0);
SELECT COUNT(p.id) AS col_0_0_
FROM   Person p

SELECT COUNT(*)
FROM   Person

The INSERT statement was not executed because there was no manual flush() call.

The MANUAL flush mode is useful when using multi-request logical transactions, and only the last request should flush the persistence context.

7.5. Flush operation order

From a database perspective, a row state can be altered using either an INSERT, an UPDATE or a DELETE statement. Because entity state changes are automatically converted to SQL statements, it’s important to know which entity actions are associated with a given SQL statement.

INSERT

The INSERT statement is generated either by the EntityInsertAction or EntityIdentityInsertAction. These actions are scheduled by the persist operation, either explicitly or through cascading the PersistEvent from a parent to a child entity.

DELETE

The DELETE statement is generated by the EntityDeleteAction or OrphanRemovalAction.

UPDATE

The UPDATE statement is generated by EntityUpdateAction during flushing if the managed entity has been marked modified. The dirty checking mechanism is responsible for determining if a managed entity has been modified since it was first loaded.

Hibernate does not execute the SQL statements in the order of their associated entity state operations.

To visualize how this works, consider the following example:

Example 437. Flush operation order
Person person = entityManager.find(Person.class, 1L);
entityManager.remove(person);

Person newPerson = new Person();
newPerson.setId(2L);
newPerson.setName("John Doe");
entityManager.persist(newPerson);
INSERT INTO Person (name, id)
VALUES ('John Doe', 2L)

DELETE FROM Person WHERE id = 1

Even if we removed the first entity and then persist a new one, Hibernate is going to execute the DELETE statement after the INSERT.

The order in which SQL statements are executed is given by the ActionQueue and not by the order in which entity state operations have been previously defined.

The ActionQueue executes all operations in the following order:

  1. OrphanRemovalAction

  2. EntityInsertAction or EntityIdentityInsertAction

  3. EntityUpdateAction

  4. QueuedOperationCollectionAction

  5. CollectionRemoveAction

  6. CollectionUpdateAction

  7. CollectionRecreateAction

  8. EntityDeleteAction

8. Database Access

8.1. ConnectionProvider

As an ORM tool, probably the single most important thing you need to tell Hibernate is how to connect to your database so that it may connect on behalf of your application. This is ultimately the function of the org.hibernate.engine.jdbc.connections.spi.ConnectionProvider interface. Hibernate provides some out of the box implementations of this interface. ConnectionProvider is also an extension point so you can also use custom implementations from third parties or written yourself. The ConnectionProvider to use is defined by the hibernate.connection.provider_class setting. See the org.hibernate.cfg.AvailableSettings#CONNECTION_PROVIDER

Generally speaking, applications should not have to configure a ConnectionProvider explicitly if using one of the Hibernate-provided implementations. Hibernate will internally determine which ConnectionProvider to use based on the following algorithm:

  1. If hibernate.connection.provider_class is set, it takes precedence

  2. else if hibernate.connection.datasource is set → Using DataSources

  3. else if any setting prefixed by hibernate.c3p0. is set → Using c3p0

  4. else if any setting prefixed by hibernate.proxool. is set → Using Proxool

  5. else if any setting prefixed by hibernate.hikari. is set → Using HikariCP

  6. else if any setting prefixed by hibernate.vibur. is set → Using Vibur DBCP

  7. else if any setting prefixed by hibernate.agroal. is set → Using Agroal

  8. else if hibernate.connection.url is set → Using Hibernate’s built-in (and unsupported) pooling

  9. else → User-provided Connections

8.2. Using DataSources

Hibernate can integrate with a javax.sql.DataSource for obtaining JDBC Connections. Applications would tell Hibernate about the DataSource via the (required) hibernate.connection.datasource setting which can either specify a JNDI name or would reference the actual DataSource instance. For cases where a JNDI name is given, be sure to read JNDI.

For Jakarta Persistence applications, note that hibernate.connection.datasource corresponds to jakarta.persistence.jtaDataSource or jakarta.persistence.nonJtaDataSource.

The DataSource ConnectionProvider also (optionally) accepts the hibernate.connection.username and hibernate.connection.password. If specified, the DataSource#getConnection(String username, String password) will be used. Otherwise, the no-arg form is used.

8.3. Driver Configuration

hibernate.connection.driver_class

The name of the JDBC Driver class to use

hibernate.connection.url

The JDBC connection url

hibernate.connection.*

All such setting names (except the predefined ones) will have the hibernate.connection. prefix stripped. The remaining name and the original value will be passed to the driver as a JDBC connection property

Not all properties apply to all situations. For example, if you are providing a data source, hibernate.connection.driver_class setting will not be used.

8.4. Using c3p0

To use the c3p0 integration, the application must include the hibernate-c3p0 module jar (as well as its dependencies) on the classpath.

Hibernate also provides support for applications to use c3p0 connection pooling. When c3p0 support is enabled, a number of c3p0-specific configuration settings are recognized in addition to the general ones described in Driver Configuration.

Transaction isolation of the Connections is managed by the ConnectionProvider itself. See ConnectionProvider support for transaction isolation setting.

hibernate.c3p0.min_size or c3p0.minPoolSize

The minimum size of the c3p0 pool. See c3p0 minPoolSize

hibernate.c3p0.max_size or c3p0.maxPoolSize

The maximum size of the c3p0 pool. See c3p0 maxPoolSize

hibernate.c3p0.timeout or c3p0.maxIdleTime

The Connection idle time. See c3p0 maxIdleTime

hibernate.c3p0.max_statements or c3p0.maxStatements

Controls the c3p0 PreparedStatement cache size (if using). See c3p0 maxStatements

hibernate.c3p0.acquire_increment or c3p0.acquireIncrement

Number of connections c3p0 should acquire at a time when the pool is exhausted. See c3p0 acquireIncrement

hibernate.c3p0.idle_test_period or c3p0.idleConnectionTestPeriod

Idle time before a c3p0 pooled connection is validated. See c3p0 idleConnectionTestPeriod

hibernate.c3p0.initialPoolSize

The initial c3p0 pool size. If not specified, default is to use the min pool size. See c3p0 initialPoolSize

Any other settings prefixed with hibernate.c3p0.

Will have the hibernate. portion stripped and be passed to c3p0.

Any other settings prefixed with c3p0.

Get passed to c3p0 as is. See c3p0 configuration

8.5. Using Proxool

To use the Proxool integration, the application must include the hibernate-proxool module jar (as well as its dependencies) on the classpath.

Hibernate also provides support for applications to use Proxool connection pooling.

Transaction isolation of the Connections is managed by the ConnectionProvider itself. See ConnectionProvider support for transaction isolation setting.

8.5.1. Using existing Proxool pools

Controlled by the hibernate.proxool.existing_pool setting. If set to true, this ConnectionProvider will use an already existing Proxool pool by alias as indicated by the hibernate.proxool.pool_alias setting.

8.5.2. Configuring Proxool via XML

The hibernate.proxool.xml setting names a Proxool configuration XML file to be loaded as a classpath resource and loaded by Proxool’s JAXPConfigurator. See proxool configuration. hibernate.proxool.pool_alias must be set to indicate which pool to use.

8.5.3. Configuring Proxool via Properties

The hibernate.proxool.properties setting names a Proxool configuration properties file to be loaded as a classpath resource and loaded by Proxool’s PropertyConfigurator. See proxool configuration. hibernate.proxool.pool_alias must be set to indicate which pool to use.

8.6. Using HikariCP

To use the HikariCP this integration, the application must include the hibernate-hikari module jar (as well as its dependencies) on the classpath.

Hibernate also provides support for applications to use HikariCP connection pool.

Set all of your Hikari settings in Hibernate prefixed by hibernate.hikari. and this ConnectionProvider will pick them up and pass them along to Hikari. Additionally, this ConnectionProvider will pick up the following Hibernate-specific properties and map them to the corresponding Hikari ones (any hibernate.hikari. prefixed ones have precedence):

hibernate.connection.driver_class

Mapped to Hikari’s driverClassName setting

hibernate.connection.url

Mapped to Hikari’s jdbcUrl setting

hibernate.connection.username

Mapped to Hikari’s username setting

hibernate.connection.password

Mapped to Hikari’s password setting

hibernate.connection.isolation

Mapped to Hikari’s transactionIsolation setting. See ConnectionProvider support for transaction isolation setting. Note that Hikari only supports JDBC standard isolation levels (apparently).

hibernate.connection.autocommit

Mapped to Hikari’s autoCommit setting

8.7. Using Vibur DBCP

To use the Vibur DBCP integration, the application must include the hibernate-vibur module jar (as well as its dependencies) on the classpath.

Hibernate also provides support for applications to use Vibur DBCP connection pool.

Set all of your Vibur settings in Hibernate prefixed by hibernate.vibur. and this ConnectionProvider will pick them up and pass them along to Vibur DBCP. Additionally, this ConnectionProvider will pick up the following Hibernate-specific properties and map them to the corresponding Vibur ones (any hibernate.vibur. prefixed ones have precedence):

hibernate.connection.driver_class

Mapped to Vibur’s driverClassName setting

hibernate.connection.url

Mapped to Vibur’s jdbcUrl setting

hibernate.connection.username

Mapped to Vibur’s username setting

hibernate.connection.password

Mapped to Vibur’s password setting

hibernate.connection.isolation

Mapped to Vibur’s defaultTransactionIsolationValue setting. See ConnectionProvider support for transaction isolation setting.

hibernate.connection.autocommit

Mapped to Vibur’s defaultAutoCommit setting

8.8. Using Agroal

To use the Agroal integration, the application must include the hibernate-agroal module jar (as well as its dependencies) on the classpath.

Hibernate also provides support for applications to use Agroal connection pool.

Set all of your Agroal settings in Hibernate prefixed by hibernate.agroal. and this ConnectionProvider will pick them up and pass them along to Agroal connection pool. Additionally, this ConnectionProvider will pick up the following Hibernate-specific properties and map them to the corresponding Agroal ones (any hibernate.agroal. prefixed ones have precedence):

hibernate.connection.driver_class

Mapped to Agroal’s driverClassName setting

hibernate.connection.url

Mapped to Agroal’s jdbcUrl setting

hibernate.connection.username

Mapped to Agroal’s principal setting

hibernate.connection.password

Mapped to Agroal’s credential setting

hibernate.connection.isolation

Mapped to Agroal’s jdbcTransactionIsolation setting. See ConnectionProvider support for transaction isolation setting.

hibernate.connection.autocommit

Mapped to Agroal’s autoCommit setting

8.9. Using Hibernate’s built-in (and unsupported) pooling

The built-in connection pool is not supported for use in a production system.

This section is here just for completeness.

8.10. User-provided Connections

It is possible to use Hibernate by simply passing a Connection to use to the Session when the Session is opened. This usage is discouraged and not discussed here.

8.11. ConnectionProvider support for transaction isolation setting

All the provided ConnectionProvider implementations, apart from DataSourceConnectionProvider, support consistent setting of transaction isolation for all Connections obtained from the underlying pool. The value for hibernate.connection.isolation can be specified in one of 3 formats:

  • the integer value accepted at the JDBC level.

  • the name of the java.sql.Connection constant field representing the isolation you would like to use. For example, TRANSACTION_REPEATABLE_READ for java.sql.Connection#TRANSACTION_REPEATABLE_READ. Note that this is only supported for JDBC standard isolation levels, not for isolation levels specific to a particular JDBC driver.

  • a short-name version of the java.sql.Connection constant field without the TRANSACTION_ prefix. For example, REPEATABLE_READ for java.sql.Connection#TRANSACTION_REPEATABLE_READ. Again, this is only supported for JDBC standard isolation levels, not for isolation levels specific to a particular JDBC driver.

8.12. Connection handling

The connection handling mode is defined by the PhysicalConnectionHandlingMode enumeration which provides the following strategies:

IMMEDIATE_ACQUISITION_AND_HOLD

The Connection will be acquired as soon as the Session is opened and held until the Session is closed.

DELAYED_ACQUISITION_AND_HOLD

The Connection will be acquired as soon as it is needed and then held until the Session is closed.

DELAYED_ACQUISITION_AND_RELEASE_AFTER_STATEMENT

The Connection will be acquired as soon as it is needed and will be released after each statement is executed.

DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION

The Connection will be acquired as soon as it is needed and will be released after each transaction is completed.

If you don’t want to use the default connection handling mode, you can specify a connection handling mode via the hibernate.connection.handling_mode configuration property. For more details, check out the Database connection properties section.

8.12.1. Transaction type and connection handling

By default, the connection handling mode is given by the underlying transaction coordinator. There are two types of transactions: RESOURCE_LOCAL (which involves a single database Connection and the transaction is controlled via the commit and rollback Connection methods) and JTA (which may involve multiple resources including database connections, JMS queues, etc).

RESOURCE_LOCAL transaction connection handling

For RESOURCE_LOCAL transactions, the connection handling mode is DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION meaning that the database connection is acquired when needed and released after the current running transaction is either committed or rolled back.

However, because Hibernate needs to make sure that the default autocommit mode is disabled on the JDBC Connection when starting a new transaction, the Connection is acquired and the autocommit mode is set to false.

If you are using a connection pool DataSource that already disabled the autocommit mode for every pooled Connection, you should set the hibernate.connection.provider_disables_autocommit to true and the database connection acquisition will be, indeed, delayed until Hibernate needs to execute the first SQL statement.

JTA transaction connection handling

For JTA transactions, the connection handling mode is DELAYED_ACQUISITION_AND_RELEASE_AFTER_STATEMENT meaning that the database connection is acquired when needed and released after each statement execution.

The reason for releasing the database connection after statement execution is because some Java EE application servers report a connection leak when a method call goes from one EJB to another. However, even if the JDBC Connection is released to the pool, the Connection is still allocated to the current executing Thread, hence when executing a subsequent statement in the current running transaction, the same Connection object reference will be obtained from the pool.

If the Java EE application server or JTA transaction manager supports switching from one EJB to another while the transaction gets propagated from the outer EJB to the inner one, and no connection leak false positive is being reported, then you should consider switching to DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION via the hibernate.connection.handling_mode configuration property.

8.12.2. User-provided connections

If the current Session was created using the SessionBuilder and a JDBC Connection was provided via the SessionBuilder#connection method, then the user-provided Connection is going to be used, and the connection handling mode will be IMMEDIATE_ACQUISITION_AND_HOLD.

Therefore for user-provided connection, the connection is acquired right away and held until the current Session is closed, without being influenced by the Jakarta Persistence or Hibernate transaction context.

8.13. Database Dialect

Although SQL is now relatively standardized—much more so than in the past—it’s still the case that each database vendor implements a different dialect of SQL that, while overlapping significantly with ANSI SQL, forms neither a subset, nor a superset, of the standard.

Hibernate abstracts over variations between dialects of SQL via the class org.hibernate.dialect.Dialect.

  • There’s a subclass of Dialect for each supported relational database in the package org.hibernate.dialect.

  • Additional community-supported Dialects are available in the separate module hibernate-community-dialects.

In Hibernate 6, it’s no longer necessary to explicitly specify a dialect using the configuration property hibernate.dialect, and so setting that property is now discouraged. (An exception is the case of custom user-written Dialects.)

9. Transactions

It is important to understand that the term transaction has many different yet related meanings in regards to persistence and Object/Relational Mapping. In most use-cases these definitions align, but that is not always the case.

  • It might refer to the physical transaction with the database.

  • It might refer to the logical notion of a transaction as related to a persistence context.

  • It might refer to the application notion of a Unit-of-Work, as defined by the archetypal pattern.

This documentation largely treats the physical and logic notions of a transaction as one-in-the-same.

9.1. Physical Transactions

Hibernate uses the JDBC API for persistence. In the world of Java, there are two well-defined mechanisms for dealing with transactions in JDBC: JDBC itself and JTA. Hibernate supports both mechanisms for integrating with transactions and allowing applications to manage physical transactions.

The transaction handling per Session is handled by the org.hibernate.resource.transaction.spi.TransactionCoordinator contract, which are built by the org.hibernate.resource.transaction.spi.TransactionCoordinatorBuilder service. TransactionCoordinatorBuilder represents a strategy for dealing with transactions whereas TransactionCoordinator represents one instance of that strategy related to a Session. Which TransactionCoordinatorBuilder implementation to use is defined by the hibernate.transaction.coordinator_class setting.

jdbc (the default for non-Jakarta Persistence applications)

Manages transactions via calls to java.sql.Connection

jta

Manages transactions via JTA. See Java EE bootstrapping

If a Jakarta Persistence application does not provide a setting for hibernate.transaction.coordinator_class, Hibernate will automatically build the proper transaction coordinator based on the transaction type for the persistence unit.

If a non-Jakarta Persistence application does not provide a setting for hibernate.transaction.coordinator_class, Hibernate will use jdbc as the default. This default will cause problems if the application actually uses JTA-based transactions. A non-Jakarta Persistence application that uses JTA-based transactions should explicitly set hibernate.transaction.coordinator_class=jta or provide a custom org.hibernate.resource.transaction.TransactionCoordinatorBuilder that builds a org.hibernate.resource.transaction.TransactionCoordinator that properly coordinates with JTA-based transactions.

For details on implementing a custom TransactionCoordinatorBuilder, or simply better understanding how it works, see the Integration Guide .

Hibernate uses JDBC connections and JTA resources directly, without adding any additional locking behavior. Hibernate does not lock objects in memory. The behavior defined by the isolation level of your database transactions does not change when you use Hibernate. The Hibernate Session acts as a transaction-scoped cache providing repeatable reads for lookup by identifier and queries that result in loading entities.

To reduce lock contention in the database, the physical database transaction needs to be as short as possible.

Long-running database transactions prevent your application from scaling to a highly-concurrent load. Do not hold a database transaction open during end-user-level work, but open it after the end-user-level work is finished.

This concept is referred to as transactional write-behind.

9.2. JTA configuration

Interaction with a JTA system is consolidated behind a single contract named org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform which exposes access to the javax.transaction.TransactionManager and javax.transaction.UserTransaction for that system as well as exposing the ability to register javax.transaction.Synchronization instances, check transaction status, etc.

Generally, JtaPlatform will need access to JNDI to resolve the JTA TransactionManager, UserTransaction, etc. See JNDI chapter for details on configuring access to JNDI.

Hibernate tries to discover the JtaPlatform it should use through the use of another service named org.hibernate.engine.transaction.jta.platform.spi.JtaPlatformResolver. If that resolution does not work, or if you wish to provide a custom implementation you will need to specify the hibernate.transaction.jta.platform setting. Hibernate provides many implementations of the JtaPlatform contract, all with short names:

Atomikos

JtaPlatform for Atomikos.

Borland

JtaPlatform for the Borland Enterprise Server.

Bitronix

JtaPlatform for Bitronix.

JBossAS

JtaPlatform for Arjuna/JBossTransactions/Narayana when used within the JBoss/WildFly Application Server.

JBossTS

JtaPlatform for Arjuna/JBossTransactions/Narayana when used standalone.

JOnAS

JtaPlatform for JOTM when used within JOnAS.

JOTM

JtaPlatform for JOTM when used standalone.

JRun4

JtaPlatform for the JRun 4 Application Server.

OC4J

JtaPlatform for Oracle’s OC4J container.

Orion

JtaPlatform for the Orion Application Server.

Resin

JtaPlatform for the Resin Application Server.

SapNetWeaver

JtaPlatform for the SAP NetWeaver Application Server.

SunOne

JtaPlatform for the SunOne Application Server.

Weblogic

JtaPlatform for the Weblogic Application Server.

WebSphere

JtaPlatform for older versions of the WebSphere Application Server.

WebSphereExtended

JtaPlatform for newer versions of the WebSphere Application Server.

9.3. Hibernate Transaction API

Hibernate provides an API for helping to isolate applications from the differences in the underlying physical transaction system in use. Based on the configured TransactionCoordinatorBuilder, Hibernate will simply do the right thing when this transaction API is used by the application. This allows your applications and components to be more portable to move around into different environments.

To use this API, you would obtain the org.hibernate.Transaction from the Session. Transaction allows for all the normal operations you’d expect: begin, commit and rollback, and it even exposes some cool methods like:

markRollbackOnly

that works in both JTA and JDBC.

getTimeout and setTimeout

that again work in both JTA and JDBC.

registerSynchronization

that allows you to register JTA Synchronizations even in non-JTA environments. In fact, in both JTA and JDBC environments, these Synchronizations are kept locally by Hibernate. In JTA environments, Hibernate will only ever register one single Synchronization with the TransactionManager to avoid ordering problems.

Additionally, it exposes a getStatus method that returns an org.hibernate.resource.transaction.spi.TransactionStatus enum. This method checks with the underlying transaction system if needed, so care should be taken to minimize its use; it can have a big performance impact in certain JTA setups.

Let’s take a look at using the Transaction API in the various environments.

Example 438. Using Transaction API in JDBC
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
		// "jdbc" is the default, but for explicitness
		.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jdbc")
		.build();

Metadata metadata = new MetadataSources(serviceRegistry)
		.addAnnotatedClass(Customer.class)
		.getMetadataBuilder()
		.build();

SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
		.build();

Session session = sessionFactory.openSession();
try {
	// calls Connection#setAutoCommit(false) to
	// signal start of transaction
	session.getTransaction().begin();

	session.createMutationQuery("UPDATE customer set NAME = 'Sir. '||NAME")
			.executeUpdate();

	// calls Connection#commit(), if an error
	// happens we attempt a rollback
	session.getTransaction().commit();
}
catch (Exception e) {
	// we may need to rollback depending on
	// where the exception happened
	if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
			|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
		session.getTransaction().rollback();
	}
	// handle the underlying error
}
finally {
	session.close();
	sessionFactory.close();
}
Example 439. Using Transaction API in JTA (CMT)
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
		// "jdbc" is the default, but for explicitness
		.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jta")
		.build();

Metadata metadata = new MetadataSources(serviceRegistry)
		.addAnnotatedClass(Customer.class)
		.getMetadataBuilder()
		.build();

SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
		.build();

// Note: depending on the JtaPlatform used and some optional settings,
// the underlying transactions here will be controlled through either
// the JTA TransactionManager or UserTransaction

Session session = sessionFactory.openSession();
try {
	// Since we are in CMT, a JTA transaction would
	// already have been started.  This call essentially
	// no-ops
	session.getTransaction().begin();

	Number customerCount = (Number) session.createSelectionQuery("select count(c) from Customer c").uniqueResult();

	// Since we did not start the transaction (CMT),
	// we also will not end it.  This call essentially
	// no-ops in terms of transaction handling.
	session.getTransaction().commit();
}
catch (Exception e) {
	// again, the rollback call here would no-op (aside from
	// marking the underlying CMT transaction for rollback only).
	if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
			|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
		session.getTransaction().rollback();
	}
	// handle the underlying error
}
finally {
	session.close();
	sessionFactory.close();
}
Example 440. Using Transaction API in JTA (BMT)
StandardServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
		// "jdbc" is the default, but for explicitness
		.applySetting(AvailableSettings.TRANSACTION_COORDINATOR_STRATEGY, "jta")
		.build();

Metadata metadata = new MetadataSources(serviceRegistry)
		.addAnnotatedClass(Customer.class)
		.getMetadataBuilder()
		.build();

SessionFactory sessionFactory = metadata.getSessionFactoryBuilder()
		.build();

// Note: depending on the JtaPlatform used and some optional settings,
// the underlying transactions here will be controlled through either
// the JTA TransactionManager or UserTransaction

Session session = sessionFactory.openSession();
try {
	// Assuming a JTA transaction is not already active,
	// this call the TM/UT begin method.  If a JTA
	// transaction is already active, we remember that
	// the Transaction associated with the Session did
	// not "initiate" the JTA transaction and will later
	// nop-op the commit and rollback calls...
	session.getTransaction().begin();

	session.persist(new Customer());
	Customer customer = (Customer) session.createSelectionQuery("select c from Customer c").uniqueResult();

	// calls TM/UT commit method, assuming we are initiator.
	session.getTransaction().commit();
}
catch (Exception e) {
	// we may need to rollback depending on
	// where the exception happened
	if (session.getTransaction().getStatus() == TransactionStatus.ACTIVE
			|| session.getTransaction().getStatus() == TransactionStatus.MARKED_ROLLBACK) {
		// calls TM/UT commit method, assuming we are initiator;
		// otherwise marks the JTA transaction for rollback only
		session.getTransaction().rollback();
	}
	// handle the underlying error
}
finally {
	session.close();
	sessionFactory.close();
}

In the CMT case, we really could have omitted all of the Transaction calls. But the point of the examples was to show that the Transaction API really does insulate your code from the underlying transaction mechanism. In fact, if you strip away the comments and the single configuration setting supplied at bootstrap, the code is exactly the same in all 3 examples. In other words, we could develop that code and drop it, as-is, in any of the 3 transaction environments.

The Transaction API tries hard to make the experience consistent across all environments. To that end, it generally defers to the JTA specification when there are differences (for example automatically trying rollback on a failed commit).

9.4. Contextual sessions

Most applications using Hibernate need some form of contextual session, where a given session is in effect throughout the scope of a given context. However, across applications the definition of what constitutes a context is typically different; different contexts define different scopes to the notion of current. Applications using Hibernate prior to version 3.0 tended to utilize either home-grown ThreadLocal-based contextual sessions, helper classes such as HibernateUtil, or utilized third-party frameworks, such as Spring or Pico, which provided proxy/interception-based contextual sessions.

Starting with version 3.0.1, Hibernate added the SessionFactory.getCurrentSession() method. Initially, this assumed usage of JTA transactions, where the JTA transaction defined both the scope and context of a current session. Given the maturity of the numerous stand-alone JTA TransactionManager implementations, most, if not all, applications should be using JTA transaction management, whether or not they are deployed into a J2EE container. Based on that, the JTA-based contextual sessions are all you need to use.

However, as of version 3.1, the processing behind SessionFactory.getCurrentSession() is now pluggable. To that end, a new extension interface, org.hibernate.context.spi.CurrentSessionContext, and a new configuration parameter, hibernate.current_session_context_class, have been added to allow pluggability of the scope and context of defining current sessions.

See the Javadocs for the org.hibernate.context.spi.CurrentSessionContext interface for a detailed discussion of its contract. It defines a single method, currentSession(), by which the implementation is responsible for tracking the current contextual session. Out-of-the-box, Hibernate comes with three implementations of this interface:

org.hibernate.context.internal.JTASessionContext

current sessions are tracked and scoped by a JTA transaction. The processing here is exactly the same as in the older JTA-only approach.

org.hibernate.context.internal.ThreadLocalSessionContext

current sessions are tracked by thread of execution. See the Javadocs for more details.

org.hibernate.context.internal.ManagedSessionContext

current sessions are tracked by thread of execution. However, you are responsible to bind and unbind a Session instance with static methods on this class; it does not open, flush, or close a Session.

Typically, the value of this parameter would just name the implementation class to use. For the three out-of-the-box implementations, however, there are three corresponding short names: jta, thread, and managed.

The first two implementations provide a one session - one database transaction programming model. This is also known and used as session-per-request. The beginning and end of a Hibernate session is defined by the duration of a database transaction. If you use programmatic transaction demarcation in plain Java SE without JTA, you are advised to use the Hibernate Transaction API to hide the underlying transaction system from your code. If you use JTA, you can utilize the JTA interfaces to demarcate transactions. If you execute in an EJB container that supports CMT, transaction boundaries are defined declaratively and you do not need any transaction or session demarcation operations in your code.

The hibernate.current_session_context_class configuration parameter defines which org.hibernate.context.spi.CurrentSessionContext implementation should be used. For backward compatibility, if this configuration parameter is not set but a org.hibernate.engine.transaction.jta.platform.spi.JtaPlatform is configured, Hibernate will use the org.hibernate.context.internal.JTASessionContext.

9.5. Transactional patterns (and anti-patterns)

9.5.1. Session-per-operation anti-pattern

This is an anti-pattern of opening and closing a Session for each database call in a single thread. It is also an anti-pattern in terms of database transactions. Group your database calls into a planned sequence. In the same way, do not auto-commit after every SQL statement in your application. Hibernate disables or expects the application server to disable, auto-commit mode immediately. Database transactions are never optional. All communication with a database must be encapsulated by a transaction. Avoid auto-commit behavior for reading data because many small transactions are unlikely to perform better than one clearly-defined unit of work, and are more difficult to maintain and extend.

Using auto-commit does not circumvent database transactions.

Instead, when in auto-commit mode, JDBC drivers simply perform each call in an implicit transaction call. It is as if your application called commit after each and every JDBC call.

9.5.2. Session-per-request pattern

This is the most common transaction pattern. The term request here relates to the concept of a system that reacts to a series of requests from a client/user. Web applications are a prime example of this type of system, though certainly not the only one. At the beginning of handling such a request, the application opens a Hibernate Session, starts a transaction, performs all data related work, ends the transaction and closes the Session. The crux of the pattern is the one-to-one relationship between the transaction and the Session.

Within this pattern, there is a common technique of defining a current session to simplify the need of passing this Session around to all the application components that may need access to it. Hibernate provides support for this technique through the getCurrentSession method of the SessionFactory. The concept of a current session has to have a scope that defines the bounds in which the notion of current is valid. This is the purpose of the org.hibernate.context.spi.CurrentSessionContext contract.

There are 2 reliable defining scopes:

  • First is a JTA transaction because it allows a callback hook to know when it is ending, which gives Hibernate a chance to close the Session and clean up. This is represented by the org.hibernate.context.internal.JTASessionContext implementation of the org.hibernate.context.spi.CurrentSessionContext contract. Using this implementation, a Session will be opened the first time getCurrentSession is called within that transaction.

  • Secondly is this application request cycle itself. This is best represented with the org.hibernate.context.internal.ManagedSessionContext implementation of the org.hibernate.context.spi.CurrentSessionContext contract. Here an external component is responsible for managing the lifecycle and scoping of a current session. At the start of such a scope, ManagedSessionContext#bind() method is called passing in the Session. In the end, its unbind() method is called. Some common examples of such external components include:

    • javax.servlet.Filter implementation

    • AOP interceptor with a pointcut on the service methods

    • A proxy/interception container

The getCurrentSession() method has one downside in a JTA environment. If you use it, after_statement connection release mode is also used by default. Due to a limitation of the JTA specification, Hibernate cannot automatically clean up any unclosed ScrollableResults or Iterator instances returned by scroll() or iterate(). Release the underlying database cursor by calling ScrollableResults#close() or Hibernate.close(Iterator) explicitly from a finally block.

9.5.3. Conversations (application-level transactions)

The session-per-request pattern is not the only valid way of designing units of work. Many business processes require a whole series of interactions with the user that are interleaved with database accesses. In web and enterprise applications, it is not acceptable for a database transaction to span a user interaction. Consider the following example:

The first screen of a dialog opens. The data seen by the user is loaded in a particular Session and database transaction. The user is free to modify the objects.

The user uses a UI element to save their work after five minutes of editing. The modifications are made persistent. The user also expects to have exclusive access to the data during the edit session.

Even though we have multiple databases access here, from the point of view of the user, this series of steps represents a single unit of work. There are many ways to implement this in your application.

A first naive implementation might keep the Session and database transaction open while the user is editing, using database-level locks to prevent other users from modifying the same data and to guarantee isolation and atomicity. This is an anti-pattern because lock contention is a bottleneck which will prevent scalability in the future.

Several database transactions are used to implement the conversation. In this case, maintaining isolation of business processes becomes the partial responsibility of the application tier. A single conversation usually spans several database transactions. These multiple database accesses can only be atomic as a whole if only one of these database transactions (typically the last one) stores the updated data. All others only read data. A common way to receive this data is through a wizard-style dialog spanning several request/response cycles. Hibernate includes some features which make this easy to implement.

Automatic Versioning

Hibernate can perform automatic optimistic concurrency control for you. It can automatically detect (at the end of the conversation) if a concurrent modification occurred during user think time.

Detached Objects

If you decide to use the session-per-request pattern, all loaded instances will be in the detached state during user think time. Hibernate allows you to reattach the objects and persist the modifications. The pattern is called session-per-request-with-detached-objects. Automatic versioning is used to isolate concurrent modifications.

Extended Session

The Hibernate Session can be disconnected from the underlying JDBC connection after the database transaction has been committed and reconnected when a new client request occurs. This pattern is known as session-per-conversation and makes even reattachment unnecessary. Automatic versioning is used to isolate concurrent modifications, and the Session will not be allowed to flush automatically, only explicitly.

Session-per-request-with-detached-objects and session-per-conversation each have advantages and disadvantages.

9.5.4. Session-per-application anti-pattern

The session-per-application is also considered an anti-pattern. The Hibernate Session, like the Jakarta Persistence EntityManager, is not a thread-safe object and it is intended to be confined to a single thread at once. If the Session is shared among multiple threads, there will be race conditions as well as visibility issues, so beware of this.

An exception thrown by Hibernate means you have to rollback your database transaction and close the Session immediately. If your Session is bound to the application, you have to stop the application. Rolling back the database transaction does not put your business objects back into the state they were at the start of the transaction. This means that the database state and the business objects will be out of sync. Usually, this is not a problem because exceptions are not recoverable and you will have to start over after rollback anyway.

For more details, check out the exception handling section in Persistence Context chapter.

The Session caches every object that is in a persistent state (watched and checked for dirty state by Hibernate). If you keep it open for a long time or simply load too much data, it will grow endlessly until you get an OutOfMemoryException. One solution is to call clear() and evict() to manage the Session cache, but you should consider a Stored Procedure if you need mass data operations. Some solutions are shown in the Batching chapter. Keeping a Session open for the duration of a user session also means a higher probability of stale data.

10. JNDI

Hibernate does optionally interact with JNDI on the application’s behalf. Generally, it does this when the application:

  • has asked the SessionFactory be bound to JNDI

  • has specified a DataSource to use by JNDI name

  • is using JTA transactions and the JtaPlatform needs to do JNDI lookups for TransactionManager, UserTransaction, etc

All of these JNDI calls route through a single service whose role is org.hibernate.engine.jndi.spi.JndiService. The standard JndiService accepts a number of configuration settings:

Any other settings prefixed with hibernate.jndi. will be collected and passed along to the JNDI provider.

The standard JndiService assumes that all JNDI calls are relative to the same InitialContext. If your application uses multiple naming servers for whatever reason, you will need a custom JndiService implementation to handle those details.

11. Locking

In a relational database, locking refers to actions taken to prevent data from changing between the time it is read and the time is used.

Your locking strategy can be either optimistic or pessimistic.

Optimistic

Optimistic locking assumes that multiple transactions can complete without affecting each other, and that therefore transactions can proceed without locking the data resources that they affect. Before committing, each transaction verifies that no other transaction has modified its data. If the check reveals conflicting modifications, the committing transaction rolls back.

Pessimistic

Pessimistic locking assumes that concurrent transactions will conflict with each other, and requires resources to be locked after they are read and only unlocked after the application has finished using the data.

Hibernate provides mechanisms for implementing both types of locking in your applications.

11.1. Optimistic

When your application uses long transactions or conversations that span several database transactions, you can store versioning data so that if the same entity is updated by two conversations, the last to commit changes is informed of the conflict, and does not override the other conversation’s work. This approach guarantees some isolation, but scales well and works particularly well in read-often-write-sometimes situations.

Hibernate provides two different mechanisms for storing versioning information, a dedicated version number or a timestamp.

A version or timestamp property can never be null for a detached instance. Hibernate detects any instance with a null version or timestamp as transient, regardless of other unsaved-value strategies that you specify. Declaring a nullable version or timestamp property is an easy way to avoid problems with transitive reattachment in Hibernate, especially useful if you use assigned identifiers or composite keys.

11.1.1. Mapping optimistic locking

Jakarta Persistence defines support for optimistic locking based on either a version (sequential numeric) or timestamp strategy. To enable this style of optimistic locking simply add the jakarta.persistence.Version to the persistent attribute that defines the optimistic locking value. According to Jakarta Persistence, the valid types for these attributes are limited to:

  • int or Integer

  • short or Short

  • long or Long

  • java.sql.Timestamp

However, Hibernate allows you to use even Java 8 Date/Time types, such as Instant.

Example 441. @Version annotation mapping
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`name`")
	private String name;

	@Version
	private long version;

	//Getters and setters are omitted for brevity

}
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`name`")
	private String name;

	@Version
	private Timestamp version;

	//Getters and setters are omitted for brevity

}
@Entity(name = "Person")
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	@Column(name = "`name`")
	private String name;

	@Version
	private Instant version;

	//Getters and setters are omitted for brevity

}
Dedicated version number

The version number mechanism for optimistic locking is provided through a @Version annotation.

Example 442. @Version annotation
@Version
private long version;

Here, the version property is mapped to the version column, and the entity manager uses it to detect conflicting updates, and prevent the loss of updates that would otherwise be overwritten by a last-commit-wins strategy.

The version column can be any kind of type, as long as you define and implement the appropriate UserVersionType.

Your application is forbidden from altering the version number set by Hibernate. To artificially increase the version number, see the documentation for properties LockModeType.OPTIMISTIC_FORCE_INCREMENT or LockModeType.PESSIMISTIC_FORCE_INCREMENT check in the Hibernate Entity Manager reference documentation.

If the version number is generated by the database, such as a trigger, use the annotation @org.hibernate.annotations.Generated(GenerationTime.ALWAYS) on the version attribute.

Timestamp

Timestamps are a less reliable way of optimistic locking than version numbers but can be used by applications for other purposes as well. Timestamping is automatically used if you the @Version annotation on a Date or Calendar property type.

Example 443. Using timestamps for optimistic locking
@Version
private Date version;

The timestamp can also be generated by the database, instead of by the VM, using the @CurrentTimestamp annotation, or even @Generated(value = ALWAYS, sql = "current_timestamp").

Example 444. Database-generated version timestamp mapping
@Entity(name = "Person")
public static class Person {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	@Version @CurrentTimestamp
	private LocalDateTime version;

Now, when persisting a Person entity, Hibernate calls the database-specific current timestamp retrieval function:

Example 445. Database-generated version timestamp example
Person person = new Person();
person.setId(1L);
person.setFirstName("John");
person.setLastName("Doe");
assertNull(person.getVersion());

entityManager.persist(person);
assertNotNull(person.getVersion());
CALL current_timestamp()

INSERT INTO
    Person
    (firstName, lastName, version, id)
VALUES
    (?, ?, ?, ?)

-- binding parameter [1] as [VARCHAR]   - [John]
-- binding parameter [2] as [VARCHAR]   - [Doe]
-- binding parameter [3] as [TIMESTAMP] - [2017-05-18 12:03:03.808]
-- binding parameter [4] as [BIGINT]    - [1]
Excluding attributes

By default, every entity attribute modification is going to trigger a version incrementation. If there is an entity property which should not bump up the entity version, then you need to annotate it with the Hibernate @OptimisticLock annotation, as illustrated in the following example.

Example 446. @OptimisticLock mapping example
@Entity(name = "Phone")
public static class Phone {

	@Id
	private Long id;

	@Column(name = "`number`")
	private String number;

	@OptimisticLock(excluded = true)
	private long callCount;

	@Version
	private Long version;

	//Getters and setters are omitted for brevity

	public void incrementCallCount() {
		this.callCount++;
	}
}

This way, if one thread modifies the Phone number while a second thread increments the callCount attribute, the two concurrent transactions are not going to conflict as illustrated by the following example.

Example 447. @OptimisticLock exlude attribute example
doInJPA(this::entityManagerFactory, entityManager -> {
	Phone phone = entityManager.find(Phone.class, 1L);
	phone.setNumber("+123-456-7890");

	doInJPA(this::entityManagerFactory, _entityManager -> {
		Phone _phone = _entityManager.find(Phone.class, 1L);
		_phone.incrementCallCount();

		log.info("Bob changes the Phone call count");
	});

	log.info("Alice changes the Phone number");
});
-- Bob changes the Phone call count

update
    Phone
set
    callCount = 1,
    "number" = '123-456-7890',
    version = 0
where
    id = 1
    and version = 0

-- Alice changes the Phone number

update
    Phone
set
    callCount = 0,
    "number" = '+123-456-7890',
    version = 1
where
    id = 1
    and version = 0

When Bob changes the Phone entity callCount, the entity version is not bumped up. That’s why Alice’s UPDATE succeeds since the entity version is still 0, even if Bob has changed the record since Alice loaded it.

Although there is no conflict between Bob and Alice, Alice’s UPDATE overrides Bob’s change to the callCount attribute.

For this reason, you should only use this feature if you can accommodate lost updates on the excluded entity properties.

Versionless optimistic locking

Although the default @Version property optimistic locking mechanism is sufficient in many situations, sometimes, you need rely on the actual database row column values to prevent lost updates.

Hibernate supports a form of optimistic locking that does not require a dedicated "version attribute". This is also useful for use with modeling legacy schemas.

The idea is that you can get Hibernate to perform "version checks" using either all of the entity’s attributes or just the attributes that have changed. This is achieved through the use of the @OptimisticLocking annotation which defines a single attribute of type org.hibernate.annotations.OptimisticLockType.

There are 4 available OptimisticLockTypes:

NONE

optimistic locking is disabled even if there is a @Version annotation present

VERSION (the default)

performs optimistic locking based on a @Version as described above

ALL

performs optimistic locking based on all fields as part of an expanded WHERE clause restriction for the UPDATE/DELETE SQL statements

DIRTY

performs optimistic locking based on dirty fields as part of an expanded WHERE clause restriction for the UPDATE/DELETE SQL statements

Versionless optimistic locking using OptimisticLockType.ALL
Example 448. OptimisticLockType.ALL mapping example
@Entity(name = "Person")
@OptimisticLocking(type = OptimisticLockType.ALL)
@DynamicUpdate
public static class Person {

	@Id
	private Long id;

	@Column(name = "`name`")
	private String name;

	private String country;

	private String city;

	@Column(name = "created_on")
	private Timestamp createdOn;

	//Getters and setters are omitted for brevity
}

When you need to modify the Person entity above:

Example 449. OptimisticLockType.ALL update example
Person person = entityManager.find(Person.class, 1L);
person.setCity("Washington D.C.");
UPDATE
    Person
SET
    city=?
WHERE
    id=?
    AND city=?
    AND country=?
    AND created_on=?
    AND "name"=?

-- binding parameter [1] as [VARCHAR] - [Washington D.C.]
-- binding parameter [2] as [BIGINT] - [1]
-- binding parameter [3] as [VARCHAR] - [New York]
-- binding parameter [4] as [VARCHAR] - [US]
-- binding parameter [5] as [TIMESTAMP] - [2016-11-16 16:05:12.876]
-- binding parameter [6] as [VARCHAR] - [John Doe]

As you can see, all the columns of the associated database row are used in the WHERE clause. If any column has changed after the row was loaded, there won’t be any match, and a StaleStateException or an OptimisticEntityLockException is going to be thrown.

When using OptimisticLockType.ALL, you should also use @DynamicUpdate because the UPDATE statement must take into consideration all the entity property values.

Versionless optimistic locking using OptimisticLockType.DIRTY

The OptimisticLockType.DIRTY differs from OptimisticLockType.ALL in that it only takes into consideration the entity properties that have changed since the entity was loaded in the currently running Persistence Context.

Example 450. OptimisticLockType.DIRTY mapping example
@Entity(name = "Person")
@OptimisticLocking(type = OptimisticLockType.DIRTY)
@DynamicUpdate
public static class Person {

	@Id
	private Long id;

	@Column(name = "`name`")
	private String name;

	private String country;

	private String city;

	@Column(name = "created_on")
	private Timestamp createdOn;

	//Getters and setters are omitted for brevity
}

When you need to modify the Person entity above:

Example 451. OptimisticLockType.DIRTY update example
Person person = entityManager.find(Person.class, 1L);
person.setCity("Washington D.C.");
UPDATE
    Person
SET
    city=?
WHERE
    id=?
    and city=?

-- binding parameter [1] as [VARCHAR] - [Washington D.C.]
-- binding parameter [2] as [BIGINT] - [1]
-- binding parameter [3] as [VARCHAR] - [New York]

This time, only the database column that has changed was used in the WHERE clause.

The main advantage of OptimisticLockType.DIRTY over OptimisticLockType.ALL and the default OptimisticLockType.VERSION used implicitly along with the @Version mapping, is that it allows you to minimize the risk of OptimisticEntityLockException across non-overlapping entity property changes.

When using OptimisticLockType.DIRTY, you should also use @DynamicUpdate because the UPDATE statement must take into consideration all the dirty entity property values, and also the @SelectBeforeUpdate annotation so that detached entities are properly handled by the Session#update(entity) operation.

11.2. Pessimistic

Typically, you only need to specify an isolation level for the JDBC connections and let the database handle locking issues. If you do need to obtain exclusive pessimistic locks or re-obtain locks at the start of a new transaction, Hibernate gives you the tools you need.

Hibernate always uses the locking mechanism of the database, and never lock objects in memory.

11.3. LockMode and LockModeType

Long before Java Persistence 1.0, Hibernate already defined various explicit locking strategies through its LockMode enumeration. Jakarta Persistence comes with its own LockModeType enumeration which defines similar strategies as the Hibernate-native LockMode.

LockModeType LockMode Description

NONE

NONE

The absence of a lock. All objects switch to this lock mode at the end of a Transaction. Objects associated with the session via a call to update() or saveOrUpdate() also start out in this lock mode.

READ and OPTIMISTIC

READ

The entity version is checked towards the end of the currently running transaction.

WRITE and OPTIMISTIC_FORCE_INCREMENT

WRITE

The entity version is incremented automatically even if the entity has not changed.

PESSIMISTIC_FORCE_INCREMENT

PESSIMISTIC_FORCE_INCREMENT

The entity is locked pessimistically and its version is incremented automatically even if the entity has not changed.

PESSIMISTIC_READ

PESSIMISTIC_READ

The entity is locked pessimistically using a shared lock if the database supports such a feature. Otherwise, an explicit lock is used.

PESSIMISTIC_WRITE

PESSIMISTIC_WRITE, UPGRADE

The entity is locked using an explicit lock.

PESSIMISTIC_WRITE with a jakarta.persistence.lock.timeout setting of 0

UPGRADE_NOWAIT

The lock acquisition request fails fast if the row s already locked.

PESSIMISTIC_WRITE with a jakarta.persistence.lock.timeout setting of -2

UPGRADE_SKIPLOCKED

The lock acquisition request skips the already locked rows. It uses a SELECT …​ FOR UPDATE SKIP LOCKED in Oracle and PostgreSQL 9.5, or SELECT …​ with (rowlock, updlock, readpast) in SQL Server.

The explicit user request mentioned above occurs as a consequence of any of the following actions:

  • a call to Session.load(), specifying a LockMode.

  • a call to Session.lock().

  • a call to Query.setLockMode().

If you call Session.load() with option UPGRADE, UPGRADE_NOWAIT or UPGRADE_SKIPLOCKED, and the requested object is not already loaded by the session, the object is loaded using SELECT …​ FOR UPDATE.

If you call load() for an object that is already loaded with a less restrictive lock than the one you request, Hibernate calls lock() for that object.

Session.lock() performs a version number check if the specified lock mode is READ, UPGRADE, UPGRADE_NOWAIT or UPGRADE_SKIPLOCKED. In the case of UPGRADE, UPGRADE_NOWAIT or UPGRADE_SKIPLOCKED, the SELECT …​ FOR UPDATE syntax is used.

If the requested lock mode is not supported by the database, Hibernate uses an appropriate alternate mode instead of throwing an exception. This ensures that applications are portable.

11.4. Jakarta Persistence locking query hints

Jakarta Persistence defined two locking-related query hints:

jakarta.persistence.lock.timeout

it gives the number of milliseconds a lock acquisition request will wait before throwing an exception

jakarta.persistence.lock.scope

defines the scope of the lock acquisition request. The scope can either be NORMAL (default value) or EXTENDED. The EXTENDED scope will cause a lock acquisition request to be passed to other owned table structured (e.g. @Inheritance(strategy=InheritanceType.JOINED), @ElementCollection)

Example 452. jakarta.persistence.lock.timeout example
entityManager.find(
	Person.class, id, LockModeType.PESSIMISTIC_WRITE,
	Collections.singletonMap("jakarta.persistence.lock.timeout", 200)
);
SELECT explicitlo0_.id     AS id1_0_0_,
       explicitlo0_."name" AS name2_0_0_
FROM   person explicitlo0_
WHERE  explicitlo0_.id = 1
FOR UPDATE wait 2

Not all JDBC database drivers support setting a timeout value for a locking request. If not supported, the Hibernate dialect ignores this query hint.

The jakarta.persistence.lock.scope is not yet supported as specified by the Jakarta Persistence standard.

11.5. Session.lock()

The following example shows how to obtain a shared database lock.

Example 453. session.lock() example
Person person = entityManager.find(Person.class, id);
Session session = entityManager.unwrap(Session.class);
LockOptions lockOptions = new LockOptions(LockMode.PESSIMISTIC_READ, LockOptions.NO_WAIT);
session.lock(person, lockOptions);
SELECT p1_0.id,
       p1_0."name"
FROM   Person p1_0
WHERE  p1_0.id = 1

SELECT id
FROM   Person
WHERE  id = 1
FOR    UPDATE

11.6. Follow-on-locking

When using Oracle, the FOR UPDATE exclusive locking clause cannot be used with:

  • DISTINCT

  • GROUP BY

  • UNION

  • inlined views (derived tables), therefore, affecting the legacy Oracle pagination mechanism as well.

For this reason, Hibernate uses secondary selects to lock the previously fetched entities.

Example 454. Follow-on-locking example
List<Person> persons = entityManager.createQuery(
	"select DISTINCT p from Person p", Person.class)
.setLockMode(LockModeType.PESSIMISTIC_WRITE)
.getResultList();
SELECT DISTINCT p.id as id1_0_, p."name" as name2_0_
FROM Person p

SELECT id
FROM Person
WHERE id = 1 FOR UPDATE

SELECT id
FROM Person
WHERE id = 2 FOR UPDATE

To avoid the N+1 query problem, a separate query can be used to apply the lock using the associated entity identifiers.

Example 455. Secondary query entity locking
List<Person> persons = entityManager.createQuery(
	"select DISTINCT p from Person p", Person.class)
.getResultList();

entityManager.createQuery(
	"select p.id from Person p where p in :persons")
.setLockMode(LockModeType.PESSIMISTIC_WRITE)
.setParameter("persons", persons)
.getResultList();
SELECT DISTINCT p.id as id1_0_, p."name" as name2_0_
FROM Person p

SELECT p.id as col_0_0_
FROM Person p
WHERE p.id IN ( 1 , 2 )
FOR UPDATE

The lock request was moved from the original query to a secondary one which takes the previously fetched entities to lock their associated database records.

Prior to Hibernate 5.2.1, the follow-on-locking mechanism was applied uniformly to any locking query executing on Oracle. Since 5.2.1, the Oracle Dialect tries to figure out if the current query demands the follow-on-locking mechanism.

Even more important is that you can overrule the default follow-on-locking detection logic and explicitly enable or disable it on a per query basis.

Example 456. Disabling the follow-on-locking mechanism explicitly
List<Person> persons = entityManager.createQuery(
	"select p from Person p", Person.class)
.setMaxResults(10)
.unwrap(Query.class)
.setLockOptions(
	new LockOptions(LockMode.PESSIMISTIC_WRITE)
		.setFollowOnLocking(false))
.getResultList();
SELECT *
FROM (
    SELECT p.id as id1_0_, p."name" as name2_0_
    FROM Person p
)
WHERE rownum <= 10
FOR UPDATE

The follow-on-locking mechanism should be explicitly enabled only if the currently executing query fails because the FOR UPDATE clause cannot be applied, meaning that the Dialect resolving mechanism needs to be further improved.

12. Fetching

Fetching, essentially, is the process of grabbing data from the database and making it available to the application. Tuning how an application does fetching is one of the biggest factors in determining how an application will perform. Fetching too much data, in terms of width (values/columns) and/or depth (results/rows), adds unnecessary overhead in terms of both JDBC communication and ResultSet processing. Fetching too little data might cause additional fetching to be needed. Tuning how an application fetches data presents a great opportunity to influence the overall application performance.

12.1. The basics

The concept of fetching breaks down into two different questions.

  • When should the data be fetched? Now? Later?

  • How should the data be fetched?

"Now" is generally termed eager or immediate while "later" is generally termed lazy or delayed.

There are a number of scopes for defining fetching:

static

Static definition of fetching strategies is done in the mappings. The statically-defined fetch strategies are used in the absence of any dynamically defined strategies.

SELECT

Performs a separate SQL select to load the data. This can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed). This is the strategy generally termed N+1.

JOIN

Inherently an EAGER style of fetching. The data to be fetched is obtained through the use of an SQL outer join.

BATCH

Performs a separate SQL select to load a number of related data items using an IN-restriction as part of the SQL WHERE-clause based on a batch size. Again, this can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed).

SUBSELECT

Performs a separate SQL select to load associated data based on the SQL restriction used to load the owner. Again, this can either be EAGER (the second select is issued immediately) or LAZY (the second select is delayed until the data is needed).

dynamic (sometimes referred to as runtime)

The dynamic definition is really use-case centric. There are multiple ways to define dynamic fetching:

fetch profiles

defined in mappings, but can be enabled/disabled on the Session.

HQL / JPQL

both Hibernate and Jakarta Persistence Criteria queries have the ability to specify fetching, specific to said query.

entity graphs

using Jakarta Persistence EntityGraphs

fetch profile and entity graph are mutually exclusive. When both are present, entity graph would take effect and fetch profile would be ignored.

12.2. Direct fetching vs. entity queries

To see the difference between direct fetching and entity queries in regard to eagerly fetched associations, consider the following entities:

Example 457. Domain model
@Entity(name = "Department")
public static class Department {

	@Id
	private Long id;

	//Getters and setters omitted for brevity
}

@Entity(name = "Employee")
public static class Employee {

	@Id
	private Long id;

	@NaturalId
	private String username;

	@ManyToOne(fetch = FetchType.EAGER)
	private Department department;

	//Getters and setters omitted for brevity
}

The Employee entity has a @ManyToOne association to a Department which is fetched eagerly.

When issuing a direct entity fetch, Hibernate executed the following SQL query:

Example 458. Direct fetching example
Employee employee = entityManager.find(Employee.class, 1L);
select
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_,
    d.id as id1_0_1_
from
    Employee e
left outer join
    Department d
        on e.department_id=d.id
where
    e.id = 1

The LEFT OUTER JOIN clause is added to the generated SQL query because this association is required to be fetched eagerly.

On the other hand, if you are using an entity query that does not contain a JOIN FETCH directive to the Department association:

Example 459. Entity query fetching example
Employee employee = entityManager.createQuery(
		"select e " +
		"from Employee e " +
		"where e.id = :id", Employee.class)
.setParameter("id", 1L)
.getSingleResult();
select
    e.id as id1_1_,
    e.department_id as departme3_1_,
    e.username as username2_1_
from
    Employee e
where
    e.id = 1

select
    d.id as id1_0_0_
from
    Department d
where
    d.id = 1

Hibernate uses a secondary select instead. This is because the entity query fetch policy cannot be overridden, so Hibernate requires a secondary select to ensure that the EAGER association is fetched prior to returning the result to the user.

If you forget to JOIN FETCH all EAGER associations, Hibernate is going to issue a secondary select for each and every one of those which, in turn, can lead to N + 1 query issue.

For this reason, you should prefer LAZY associations.

12.3. Applying fetch strategies

Let’s consider these topics as it relates to a sample domain model and a few use cases.

Example 460. Sample domain model
	@Entity(name = "Department")
	public static class Department {

		@Id
		private Long id;

		@OneToMany(mappedBy = "department")
		private List<Employee> employees = new ArrayList<>();

		//Getters and setters omitted for brevity
	}

	@Entity(name = "Employee")
	public static class Employee {

		@Id
		private Long id;

		@NaturalId
		private String username;

		@Column(name = "pswd")
		@ColumnTransformer(
			read = "decrypt('AES', '00', pswd )",
			write = "encrypt('AES', '00', ?)"
		)
// For H2 2.0.202+ one must use the varbinary DDL type
//		@Column(name = "pswd", columnDefinition = "varbinary")
//		@ColumnTransformer(
//			read = "trim(trailing u&'\\0000' from cast(decrypt('AES', '00', pswd ) as character varying))",
//			write = "encrypt('AES', '00', ?)"
//		)
		private String password;

		private int accessLevel;

		@ManyToOne(fetch = FetchType.LAZY)
		private Department department;

		@ManyToMany(mappedBy = "employees")
		private List<Project> projects = new ArrayList<>();

		//Getters and setters omitted for brevity
	}

	@Entity(name = "Project")
	public class Project {

		@Id
		private Long id;

		@ManyToMany
		private List<Employee> employees = new ArrayList<>();

		//Getters and setters omitted for brevity
	}

The Hibernate recommendation is to statically mark all associations lazy and to use dynamic fetching strategies for eagerness.

This is unfortunately at odds with the Jakarta Persistence specification which defines that all one-to-one and many-to-one associations should be eagerly fetched by default.

Hibernate, as a Jakarta Persistence provider, honors that default.

12.4. No fetching

For the first use case, consider the application login process for an Employee. Let’s assume that login only requires access to the Employee information, not Project nor Department information.

Example 461. No fetching example
Employee employee = entityManager.createQuery(
	"select e " +
	"from Employee e " +
	"where " +
	"	e.username = :username and " +
	"	e.password = :password",
	Employee.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();

In this example, the application gets the Employee data. However, because all associations from Employee are declared as LAZY (Jakarta Persistence defines the default for collections as LAZY) no other data is fetched.

If the login process does not need access to the Employee information specifically, another fetching optimization here would be to limit the width of the query results.

Example 462. No fetching (scalar) example
Integer accessLevel = entityManager.createQuery(
	"select e.accessLevel " +
	"from Employee e " +
	"where " +
	"	e.username = :username and " +
	"	e.password = :password",
	Integer.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();

12.5. Dynamic fetching via queries

For the second use case, consider a screen displaying the Projects for an Employee. Certainly access to the Employee is needed, as is the collection of Projects for that Employee. Information about Departments, other Employees or other Projects is not needed.

Example 463. Dynamic JPQL fetching example
Employee employee = entityManager.createQuery(
	"select e " +
	"from Employee e " +
	"left join fetch e.projects " +
	"where " +
	"	e.username = :username and " +
	"	e.password = :password",
	Employee.class)
.setParameter("username", username)
.setParameter("password", password)
.getSingleResult();
Example 464. Dynamic query fetching example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<Employee> query = builder.createQuery(Employee.class);
Root<Employee> root = query.from(Employee.class);
root.fetch("projects", JoinType.LEFT);
query.select(root).where(
	builder.and(
		builder.equal(root.get("username"), username),
		builder.equal(root.get("password"), password)
	)
);
Employee employee = entityManager.createQuery(query).getSingleResult();

In this example we have an Employee and their Projects loaded in a single query shown both as an HQL query and a Jakarta Persistence Criteria query. In both cases, this resolves to exactly one database query to get all that information.

12.6. Dynamic fetching via Jakarta Persistence entity graph

Jakarta Persistence also supports a feature called EntityGraphs to provide the application developer has more control over fetch plans. It has two modes to choose from:

fetch graph

In this case, all attributes specified in the entity graph will be treated as FetchType.EAGER, and all attributes not specified will ALWAYS be treated as FetchType.LAZY.

load graph

In this case, all attributes specified in the entity graph will be treated as FetchType.EAGER, but attributes not specified use their static mapping specification.

Below is a fetch graph dynamic fetching example:

Example 465. Fetch graph example
@Entity(name = "Employee")
@NamedEntityGraph(name = "employee.projects",
	attributeNodes = @NamedAttributeNode("projects")
)
Employee employee = entityManager.find(
	Employee.class,
	userId,
	Collections.singletonMap(
		"jakarta.persistence.fetchgraph",
		entityManager.getEntityGraph("employee.projects")
	)
);

When executing a JPQL query, if an EAGER association is omitted, Hibernate will issue a secondary select for every association needed to be fetched eagerly, which can lead to N+1 query issues.

For this reason, it’s better to use LAZY associations, and only fetch them eagerly on a per-query basis.

An EntityGraph is the root of a "load plan" and must correspond to an EntityType.

12.6.1. Jakarta Persistence (key) subgraphs

A sub-graph is used to control the fetching of sub-attributes of the AttributeNode it is applied to. It is generally defined via the @NamedSubgraph annotation.

If we have a Project parent entity which has an employees child associations, and we’d like to fetch the department for the Employee child association.

Example 466. Fetch graph with a subgraph mapping
@Entity(name = "Project")
@NamedEntityGraph(name = "project.employees",
	attributeNodes = @NamedAttributeNode(
		value = "employees",
		subgraph = "project.employees.department"
	),
	subgraphs = @NamedSubgraph(
		name = "project.employees.department",
		attributeNodes = @NamedAttributeNode("department")
	)
)
public static class Project {

	@Id
	private Long id;

	@ManyToMany
	private List<Employee> employees = new ArrayList<>();

	//Getters and setters omitted for brevity
}

When fetching this entity graph, Hibernate generates the following SQL query:

Example 467. Fetch graph with a subgraph mapping
Project project = doInJPA(this::entityManagerFactory, entityManager -> {
	return entityManager.find(
		Project.class,
		1L,
		Collections.singletonMap(
			"jakarta.persistence.fetchgraph",
			entityManager.getEntityGraph("project.employees")
		)
	);
});
select
    p.id as id1_2_0_, e.id as id1_1_1_, d.id as id1_0_2_,
    e.accessLevel as accessLe2_1_1_,
    e.department_id as departme5_1_1_,
    decrypt( 'AES', '00', e.pswd  ) as pswd3_1_1_,
    e.username as username4_1_1_,
    p_e.projects_id as projects1_3_0__,
    p_e.employees_id as employee2_3_0__
from
    Project p
inner join
    Project_Employee p_e
        on p.id=p_e.projects_id
inner join
    Employee e
        on p_e.employees_id=e.id
inner join
    Department d
        on e.department_id=d.id
where
    p.id = ?

-- binding parameter [1] as [BIGINT] - [1]

Specifying a sub-graph is only valid for an attribute (or its "key") whose type is a ManagedType. So while an EntityGraph must correspond to an EntityType, a Subgraph is legal for any ManagedType. An attribute’s key is defined as either:

  • For a singular attribute, the attribute’s type must be an IdentifiableType and that IdentifiableType must have a composite identifier. The "key sub-graph" is applied to the identifier type. The non-key sub-graph applies to the attribute’s value, which must be a ManagedType.

  • For a plural attribute, the attribute must be a Map and the Map’s key value must be a ManagedType. The "key sub-graph" is applied to the Map’s key type. In this case, the non-key sub-graph applies to the plural attribute’s value/element.

12.6.2. Jakarta Persistence SubGraph sub-typing

SubGraphs can also be sub-type specific. Given an attribute whose value is an inheritance hierarchy, we can refer to attributes of a specific sub-type using the forms of sub-graph definition that accept the sub-type Class.

12.6.3. Creating and applying Jakarta Persistence graphs from text representations

Hibernate allows the creation of Jakarta Persistence fetch/load graphs by parsing a textual representation of the graph. Generally speaking, the textual representation of a graph is a comma-separated list of attribute names, optionally including any sub-graph specifications. org.hibernate.graph.GraphParser is the starting point for such parsing operations.

Parsing a textual representation of a graph is not (yet) a part of the Jakarta Persistence specification. So the syntax described here is specific to Hibernate. We do hope to eventually make this syntax part of the Jakarta Persistence specification proper.

Example 468. Parsing a simple graph
final EntityGraph<Project> graph = GraphParser.parse(
		Project.class,
		"employees(department)",
		entityManager
);

This example actually functions exactly as Fetch graph with a subgraph mapping, just using a parsed graph rather than a named graph.

The syntax also supports defining "key sub-graphs". To specify a key sub-graph, .key is added to the end of the attribute name.

Example 469. Parsing an entity key graph
final EntityGraph<Movie> graph = GraphParser.parse(
		Movie.class,
		"cast.key(name)",
		entityManager
);
Example 470. Parsing a map key graph
final EntityGraph<Ticket> graph = GraphParser.parse(
		Ticket.class,
		"showing.key(movie(cast))",
		entityManager
);

Parsing can also handle sub-type specific sub-graphs. For example, given an entity hierarchy of LegalEntity ← (Corporation | Person | NonProfit) and an attribute named responsibleParty whose type is the LegalEntity base type we might have:

responsibleParty(Corporation: ceo)

We can even duplicate the attribute names to apply different sub-type sub-graphs:

responsibleParty(taxIdNumber), responsibleParty(Corporation: ceo), responsibleParty(NonProfit: sector)

The duplicated attribute names are handled according to the Jakarta Persistence specification which says that duplicate specification of the attribute node results in the originally registered AttributeNode to be re-used effectively merging the 2 AttributeNode specifications together. In other words, the above specification creates a single AttributeNode with 3 distinct SubGraphs. It is functionally the same as calling:

Class<Invoice> invoiceClass = ...;
jakarta.persistence.EntityGraph<Invoice> invoiceGraph = entityManager.createEntityGraph( invoiceClass );
invoiceGraph.addAttributeNode( "responsibleParty" );
invoiceGraph.addSubgraph( "responsibleParty" ).addAttributeNode( "taxIdNumber" );
invoiceGraph.addSubgraph( "responsibleParty", Corporation.class ).addAttributeNode( "ceo" );
invoiceGraph.addSubgraph( "responsibleParty", NonProfit.class ).addAttributeNode( "sector" );

12.6.4. Combining multiple Jakarta Persistence entity graphs into one

Multiple entity graphs can be combined into a single "super graph" that acts as a union. Graph from the previous example can also be built by combining separate aspect graphs into one, such as:

Example 471. Combining multiple graphs into one
final EntityGraph<Project> a = GraphParser.parse(
		Project.class, "employees(username)", entityManager
);

final EntityGraph<Project> b = GraphParser.parse(
		Project.class, "employees(password, accessLevel)", entityManager
);

final EntityGraph<Project> c = GraphParser.parse(
		Project.class, "employees(department(employees(username)))", entityManager
);

final EntityGraph<Project> all = EntityGraphs.merge(entityManager, Project.class, a, b, c);

12.7. Dynamic fetching via Hibernate profiles

Suppose we wanted to leverage loading by natural-id to obtain the Employee information in the "projects for and employee" use-case. Loading by natural-id uses the statically defined fetching strategies, but does not expose a means to define load-specific fetching. So we would leverage a fetch profile.

Example 472. Fetch profile example
@Entity(name = "Employee")
@FetchProfile(
	name = "employee.projects",
	fetchOverrides = {
		@FetchProfile.FetchOverride(
			entity = Employee.class,
			association = "projects",
			mode = FetchMode.JOIN
		)
	}
)
session.enableFetchProfile("employee.projects");
Employee employee = session.bySimpleNaturalId(Employee.class).load(username);

Here the Employee is obtained by natural-id lookup and the Employee’s Project data is fetched eagerly. If the Employee data is resolved from cache, the Project data is resolved on its own. However, if the Employee data is not resolved in cache, the Employee and Project data is resolved in one SQL query via join as we saw above.

12.8. Batch fetching

Hibernate offers the @BatchSize annotation, which can be used when fetching uninitialized entity proxies.

Considering the following entity mapping:

Example 473. @BatchSize mapping example
@Entity(name = "Department")
public static class Department {

	@Id
	private Long id;

	@OneToMany(mappedBy = "department")
	//@BatchSize(size = 5)
	private List<Employee> employees = new ArrayList<>();

	//Getters and setters omitted for brevity

}

@Entity(name = "Employee")
public static class Employee {

	@Id
	private Long id;

	@NaturalId
	private String name;

	@ManyToOne(fetch = FetchType.LAZY)
	private Department department;

	//Getters and setters omitted for brevity
}

Considering that we have previously fetched several Department entities, and now we need to initialize the employees entity collection for each particular Department, the @BatchSize annotations allows us to load multiple Employee entities in a single database roundtrip.

Example 474. @BatchSize fetching example
List<Department> departments = entityManager.createQuery(
	"select d " +
	"from Department d " +
	"inner join d.employees e " +
	"where e.name like 'John%'", Department.class)
.getResultList();

for (Department department : departments) {
	log.infof(
		"Department %d has {} employees",
		department.getId(),
		department.getEmployees().size()
	);
}
SELECT
    d.id as id1_0_
FROM
    Department d
INNER JOIN
    Employee employees1_
    ON d.id=employees1_.department_id

SELECT
    e.department_id as departme3_1_1_,
    e.id as id1_1_1_,
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.name as name2_1_0_
FROM
    Employee e
WHERE
    e.department_id IN (
        0, 2, 3, 4, 5
    )

SELECT
    e.department_id as departme3_1_1_,
    e.id as id1_1_1_,
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.name as name2_1_0_
FROM
    Employee e
WHERE
    e.department_id IN (
        6, 7, 8, 9, 1
    )

As you can see in the example above, there are only two SQL statements used to fetch the Employee entities associated with multiple Department entities.

Without @BatchSize, you’d run into a N + 1 query issue, so, instead of 2 SQL statements, there would be 10 queries needed for fetching the Employee child entities.

However, although @BatchSize is better than running into an N + 1 query issue, most of the time, a DTO projection or a JOIN FETCH is a much better alternative since it allows you to fetch all the required data with a single query.

When LockModeType is different from NONE Hibernate will not execute a batch fetching so uninitialized entity proxies will not be initialized.

This because the lock mode is different from the one of the proxies in the batch fetch queue.

12.9. The @Fetch annotation mapping

Besides the FetchType.LAZY or FetchType.EAGER Jakarta Persistence annotations, you can also use the Hibernate-specific @Fetch annotation that accepts one of the following FetchModes:

SELECT

The association is going to be fetched using a secondary select for each individual entity, collection, or join load. This mode can be used for either FetchType.EAGER or FetchType.LAZY.

JOIN

Use an outer join to load the related entities, collections or joins when using direct fetching. This mode can only be used for FetchType.EAGER.

SUBSELECT

Available for collections only. When accessing a non-initialized collection, this fetch mode will trigger loading all elements of all collections of the same role for all owners associated with the persistence context using a single secondary select.

12.10. FetchMode.SELECT

To demonstrate how FetchMode.SELECT works, consider the following entity mapping:

Example 475. FetchMode.SELECT mapping example
@Entity(name = "Department")
public static class Department {

	@Id
	private Long id;

	@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
	@Fetch(FetchMode.SELECT)
	private List<Employee> employees = new ArrayList<>();

	//Getters and setters omitted for brevity

}

@Entity(name = "Employee")
public static class Employee {

	@Id
	@GeneratedValue
	private Long id;

	@NaturalId
	private String username;

	@ManyToOne(fetch = FetchType.LAZY)
	private Department department;

	//Getters and setters omitted for brevity

}

Considering there are multiple Department entities, each one having multiple Employee entities, when executing the following test case, Hibernate fetches every uninitialized Employee collection using a secondary SELECT statement upon accessing the child collection for the first time:

Example 476. FetchMode.SELECT mapping example
List<Department> departments = entityManager.createQuery(
	"select d from Department d", Department.class)
.getResultList();

log.infof("Fetched %d Departments", departments.size());

for (Department department : departments) {
	assertEquals(3, department.getEmployees().size());
}
SELECT
    d.id as id1_0_
FROM
    Department d

-- Fetched 2 Departments

SELECT
    e.department_id as departme3_1_0_,
    e.id as id1_1_0_,
    e.id as id1_1_1_,
    e.department_id as departme3_1_1_,
    e.username as username2_1_1_
FROM
    Employee e
WHERE
    e.department_id = 1

SELECT
    e.department_id as departme3_1_0_,
    e.id as id1_1_0_,
    e.id as id1_1_1_,
    e.department_id as departme3_1_1_,
    e.username as username2_1_1_
FROM
    Employee e
WHERE
    e.department_id = 2

The more Department entities are fetched by the first query, the more secondary SELECT statements are executed to initialize the employees collections. Therefore, FetchMode.SELECT can lead to N + 1 query issue.

12.11. FetchMode.SUBSELECT

To demonstrate how FetchMode.SUBSELECT works, we are going to modify the FetchMode.SELECT mapping example to use FetchMode.SUBSELECT:

Example 477. FetchMode.SUBSELECT mapping example
@OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
@Fetch(FetchMode.SUBSELECT)
private List<Employee> employees = new ArrayList<>();

Now, we are going to fetch all Department entities that match a given filtering predicate and then navigate their employees collections.

Hibernate is going to avoid the N + 1 query issue by generating a single SQL statement to initialize all employees collections for all Department entities that were previously fetched. Instead of passing all entity identifiers, Hibernate simply reruns the previous query that fetched the Department entities.

Example 478. FetchMode.SUBSELECT mapping example
List<Department> departments = entityManager.createQuery(
	"select d " +
	"from Department d " +
	"where d.name like :token", Department.class)
.setParameter("token", "Department%")
.getResultList();

log.infof("Fetched %d Departments", departments.size());

for (Department department : departments) {
	assertEquals(3, department.getEmployees().size());
}
SELECT
    d.id as id1_0_
FROM
    Department d
where
    d.name like 'Department%'

-- Fetched 2 Departments

SELECT
    e.department_id as departme3_1_1_,
    e.id as id1_1_1_,
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_
FROM
    Employee e
WHERE
    e.department_id in (
        SELECT
            fetchmodes0_.id
        FROM
            Department fetchmodes0_
        WHERE
            d.name like 'Department%'
    )

12.12. FetchMode.JOIN

To demonstrate how FetchMode.JOIN works, we are going to modify the FetchMode.SELECT mapping example to use FetchMode.JOIN instead:

Example 479. FetchMode.JOIN mapping example
@OneToMany(mappedBy = "department")
@Fetch(FetchMode.JOIN)
private List<Employee> employees = new ArrayList<>();

Now, we are going to fetch one Department and navigate its employees collections.

The reason why we are not using a JPQL query to fetch multiple Department entities is because the FetchMode.JOIN strategy would be overridden by the query fetching directive.

To fetch multiple relationships with a JPQL query, the JOIN FETCH directive must be used instead.

Therefore, FetchMode.JOIN is useful for when entities are fetched directly, via their identifier or natural-id.

Also, the FetchMode.JOIN acts as a FetchType.EAGER strategy. Even if we mark the association as FetchType.LAZY, the FetchMode.JOIN will load the association eagerly.

Hibernate is going to avoid the secondary query by issuing an OUTER JOIN for the employees collection.

Example 480. FetchMode.JOIN mapping example
Department department = entityManager.find(Department.class, 1L);

log.infof("Fetched department: %s", department.getId());

assertEquals(3, department.getEmployees().size());
SELECT
    d.id as id1_0_0_,
    e.department_id as departme3_1_1_,
    e.id as id1_1_1_,
    e.id as id1_1_2_,
    e.department_id as departme3_1_2_,
    e.username as username2_1_2_
FROM
    Department d
LEFT OUTER JOIN
    Employee e
        on d.id = e.department_id
WHERE
    d.id = 1

-- Fetched department: 1

This time, there was no secondary query because the child collection was loaded along with the parent entity.

12.13. @LazyCollection

The @LazyCollection annotation is used to specify the lazy fetching behavior of a given collection. The possible values are given by the LazyCollectionOption enumeration:

TRUE

Load it when the state is requested.

FALSE

Eagerly load it.

EXTRA

Prefer extra queries over full collection loading.

The TRUE and FALSE values are deprecated since you should be using the Jakarta Persistence FetchType attribute of the [annotations-jpa-elementcollection], [annotations-jpa-onetomany], or [annotations-jpa-manytomany] collection.

The EXTRA value has no equivalent in the Jakarta Persistence specification, and it’s used to avoid loading the entire collection even when the collection is accessed for the first time. Each element is fetched individually using a secondary query.

Example 481. LazyCollectionOption.EXTRA mapping example
@Entity(name = "Department")
public static class Department {

	@Id
	private Long id;

	@OneToMany(mappedBy = "department", cascade = CascadeType.ALL)
	@OrderColumn(name = "order_id")
	@LazyCollection(LazyCollectionOption.EXTRA)
	private List<Employee> employees = new ArrayList<>();

	//Getters and setters omitted for brevity

}

@Entity(name = "Employee")
public static class Employee {

	@Id
	private Long id;

	@NaturalId
	private String username;

	@ManyToOne(fetch = FetchType.LAZY)
	private Department department;

	//Getters and setters omitted for brevity

}

LazyCollectionOption.EXTRA only works for ordered collections, either List(s) that are annotated with @OrderColumn or Map(s).

For bags (e.g. regular List(s) of entities that do not preserve any certain ordering), the @LazyCollection(LazyCollectionOption.EXTRA) behaves like any other FetchType.LAZY collection (the collection is fetched entirely upon being accessed for the first time).

Now, considering we have the following entities:

Example 482. LazyCollectionOption.EXTRA Domain Model example
Department department = new Department();
department.setId(1L);
entityManager.persist(department);

for (long i = 1; i <= 3; i++) {
	Employee employee = new Employee();
	employee.setId(i);
	employee.setUsername(String.format("user_%d", i));
	department.addEmployee(employee);
}

When fetching the employee collection entries by their position in the List, Hibernate generates the following SQL statements:

Example 483. LazyCollectionOption.EXTRA fetching example
Department department = entityManager.find(Department.class, 1L);

int employeeCount = department.getEmployees().size();

for(int i = 0; i < employeeCount; i++) {
	log.infof("Fetched employee: %s", department.getEmployees().get(i).getUsername());
}
SELECT
    max(order_id) + 1
FROM
    Employee
WHERE
    department_id = ?

-- binding parameter [1] as [BIGINT] - [1]

SELECT
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_
FROM
    Employee e
WHERE
    e.department_id=?
    AND e.order_id=?

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [INTEGER] - [0]

SELECT
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_
FROM
    Employee e
WHERE
    e.department_id=?
    AND e.order_id=?

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [INTEGER] - [1]

SELECT
    e.id as id1_1_0_,
    e.department_id as departme3_1_0_,
    e.username as username2_1_0_
FROM
    Employee e
WHERE
    e.department_id=?
    AND e.order_id=?

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [INTEGER] - [2]

Therefore, the child entities were fetched one after the other without triggering a full collection initialization.

For this reason, caution is advised since accessing all elements using LazyCollectionOption.EXTRA can lead to N + 1 query issue.

13. Batching

13.1. JDBC batching

JDBC offers support for batching together SQL statements that can be represented as a single PreparedStatement. Implementation wise this generally means that drivers will send the batched operation to the server in one call, which can save on network calls to the database. Hibernate can leverage JDBC batching. The following settings control this behavior.

hibernate.jdbc.batch_size

Controls the maximum number of statements Hibernate will batch together before asking the driver to execute the batch. Zero or a negative number disables this feature.

hibernate.jdbc.batch_versioned_data

Some JDBC drivers return incorrect row counts when a batch is executed. If your JDBC driver falls into this category this setting should be set to false. Otherwise, it is safe to enable this which will allow Hibernate to still batch the DML for versioned entities and still use the returned row counts for optimistic lock checks. Since 5.0, it defaults to true. Previously (versions 3.x and 4.x), it used to be false.

hibernate.jdbc.batch.builder

Names the implementation class used to manage batching capabilities. It is almost never a good idea to switch from Hibernate’s default implementation. But if you wish to, this setting would name the org.hibernate.engine.jdbc.batch.spi.BatchBuilder implementation to use.

hibernate.order_updates

Forces Hibernate to order SQL updates by the entity type and the primary key value of the items being updated. This allows for more batching to be used. It will also result in fewer transaction deadlocks in highly concurrent systems. Comes with a performance hit, so benchmark before and after to see if this actually helps or hurts your application.

hibernate.order_inserts

Forces Hibernate to order inserts to allow for more batching to be used. Comes with a performance hit, so benchmark before and after to see if this actually helps or hurts your application.

Since version 5.2, Hibernate allows overriding the global JDBC batch size given by the hibernate.jdbc.batch_size configuration property on a per Session basis.

Example 484. Hibernate specific JDBC batch size configuration on a per Session basis
entityManager
	.unwrap(Session.class)
	.setJdbcBatchSize(10);

13.2. Session batching

The following example shows an anti-pattern for batch inserts.

Example 485. Naive way to insert 100 000 entities with Hibernate
EntityManager entityManager = null;
EntityTransaction txn = null;
try {
	entityManager = entityManagerFactory().createEntityManager();

	txn = entityManager.getTransaction();
	txn.begin();

	for (int i = 0; i < 100_000; i++) {
		Person Person = new Person(String.format("Person %d", i));
		entityManager.persist(Person);
	}

	txn.commit();
} catch (RuntimeException e) {
	if (txn != null && txn.isActive()) txn.rollback();
		throw e;
} finally {
	if (entityManager != null) {
		entityManager.close();
	}
}

There are several problems associated with this example:

  1. Hibernate caches all the newly inserted Person instances in the session-level cache, so, when the transaction ends, 100 000 entities are managed by the persistence context. If the maximum memory allocated to the JVM is rather low, this example could fail with an OutOfMemoryException. The Java 1.8 JVM allocated either 1/4 of available RAM or 1Gb, which can easily accommodate 100 000 objects on the heap.

  2. long-running transactions can deplete a connection pool so other transactions don’t get a chance to proceed.

  3. JDBC batching is not enabled by default, so every insert statement requires a database roundtrip. To enable JDBC batching, set the hibernate.jdbc.batch_size property to an integer between 10 and 50.

Hibernate disables insert batching at the JDBC level transparently if you use an identity identifier generator.

13.2.1. Batch inserts

When you make new objects persistent, employ methods flush() and clear() to the session regularly, to control the size of the first-level cache.

Example 486. Flushing and clearing the Session
EntityManager entityManager = null;
EntityTransaction txn = null;
try {
	entityManager = entityManagerFactory().createEntityManager();

	txn = entityManager.getTransaction();
	txn.begin();

	int batchSize = 25;

	for (int i = 0; i < entityCount; i++) {
		if (i > 0 && i % batchSize == 0) {
			//flush a batch of inserts and release memory
			entityManager.flush();
			entityManager.clear();
		}

		Person Person = new Person(String.format("Person %d", i));
		entityManager.persist(Person);
	}

	txn.commit();
} catch (RuntimeException e) {
	if (txn != null && txn.isActive()) txn.rollback();
		throw e;
} finally {
	if (entityManager != null) {
		entityManager.close();
	}
}

13.2.2. Session scroll

When you retrieve and update data, flush() and clear() the session regularly. In addition, use method scroll() to take advantage of server-side cursors for queries that return many rows of data.

Example 487. Using scroll()
EntityManager entityManager = null;
EntityTransaction txn = null;
ScrollableResults scrollableResults = null;
try {
	entityManager = entityManagerFactory().createEntityManager();

	txn = entityManager.getTransaction();
	txn.begin();

	int batchSize = 25;

	Session session = entityManager.unwrap(Session.class);

	scrollableResults = session
		.createSelectionQuery("select p from Person p")
		.setCacheMode(CacheMode.IGNORE)
		.scroll(ScrollMode.FORWARD_ONLY);

	int count = 0;
	while (scrollableResults.next()) {
		Person Person = (Person) scrollableResults.get();
		processPerson(Person);
		if (++count % batchSize == 0) {
			//flush a batch of updates and release memory:
			entityManager.flush();
			entityManager.clear();
		}
	}

	txn.commit();
} catch (RuntimeException e) {
	if (txn != null && txn.isActive()) txn.rollback();
		throw e;
} finally {
	if (scrollableResults != null) {
		scrollableResults.close();
	}
	if (entityManager != null) {
		entityManager.close();
	}
}

If left unclosed by the application, Hibernate will automatically close the underlying resources (e.g. ResultSet and PreparedStatement) used internally by the ScrollableResults when the current transaction is ended (either commit or rollback).

However, it is good practice to close the ScrollableResults explicitly.

13.2.3. StatelessSession

StatelessSession is an alternative to Session and provides:

  • a command-oriented API

  • with no associated persistence context.

Thus, a stateless session is a slightly lower-level abstraction that’s closer to the underlying JDBC activity:

  • there’s no first-level cache,

  • the stateless session does not interact with any second-level or query cache, and

  • there’s no transactional write-behind or automatic dirty checking.

Instead, persistence operations occur synchronously when a method of StatelessSession is invoked, and entities returned by a stateless session are always detached.

A stateless session may be used to stream data to and from the database in the form of detached objects. With a stateless session, there’s no need to explicitly manage the size of the first-level cache by explicitly clearing the persistence context.

The StatelessSession API comes with certain limitations:

  • operations performed using a stateless session never cascade to associated instances,

  • collections are ignored by a stateless session,

  • lazy loading of associations is not transparent, and is only available via an explicit operation named fetch(), and

  • operations performed via a stateless session bypass Hibernate’s event model and interceptors.

Due to the lack of a first-level cache, stateless sessions are vulnerable to data aliasing effects.
Example 488. Using a StatelessSession
StatelessSession statelessSession = null;
Transaction txn = null;
ScrollableResults scrollableResults = null;
try {
	SessionFactory sessionFactory = entityManagerFactory().unwrap(SessionFactory.class);
	statelessSession = sessionFactory.openStatelessSession();

	txn = statelessSession.getTransaction();
	txn.begin();

	scrollableResults = statelessSession
		.createSelectionQuery("select p from Person p")
		.scroll(ScrollMode.FORWARD_ONLY);

	while (scrollableResults.next()) {
		Person Person = (Person) scrollableResults.get();
		processPerson(Person);
		statelessSession.update(Person);
	}

	txn.commit();
} catch (RuntimeException e) {
	if (txn != null && txn.getStatus() == TransactionStatus.ACTIVE) txn.rollback();
		throw e;
} finally {
	if (scrollableResults != null) {
		scrollableResults.close();
	}
	if (statelessSession != null) {
		statelessSession.close();
	}
}

The Person instances returned by the query are immediately detached. They are never associated with any persistence context.

The insert(), update(), and delete() operations defined by the StatelessSession interface operate directly on database rows. They cause the corresponding SQL operations to be executed immediately. They have different semantics from the save(), saveOrUpdate(), and delete() operations defined by the Session interface.

13.3. Hibernate Query Language for DML

DML, or Data Manipulation Language, refers to SQL statements such as INSERT, UPDATE, and DELETE. Hibernate provides methods for bulk SQL-style DML statement execution, in the form of Hibernate Query Language (HQL).

13.3.1. HQL/JPQL for UPDATE and DELETE

Both the Hibernate native Query Language and JPQL (Java Persistence Query Language) provide support for bulk UPDATE and DELETE.

Example 489. Pseudo-syntax for UPDATE and DELETE statements using HQL
UPDATE FROM EntityName e WHERE e.name = ?

DELETE FROM EntityName e WHERE e.name = ?

Although the FROM and WHERE clauses are optional, it is good practice to declare them explicitly.

The FROM clause can only refer to a single entity, which can be aliased. If the entity name is aliased, any property references must be qualified using that alias. If the entity name is not aliased, then it is illegal for any property references to be qualified.

Joins, either implicit or explicit, are prohibited in a bulk HQL query. You can use sub-queries in the WHERE clause, and the sub-queries themselves can contain joins.

Example 490. Executing a JPQL UPDATE, using the Query.executeUpdate()
int updatedEntities = entityManager.createQuery(
	"update Person p " +
	"set p.name = :newName " +
	"where p.name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();
Example 491. Executing an HQL UPDATE, using the Query.executeUpdate()
int updatedEntities = session.createMutationQuery(
	"update Person " +
	"set name = :newName " +
	"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();

In keeping with the EJB3 specification, HQL UPDATE statements, by default, do not effect the version or the timestamp property values for the affected entities. You can use a versioned update to force Hibernate to reset the version or timestamp property values, by adding the VERSIONED keyword after the UPDATE keyword.

Example 492. Updating the version of timestamp
int updatedEntities = session.createMutationQuery(
	"update versioned Person " +
	"set name = :newName " +
	"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();

If you use the VERSIONED statement, you cannot use custom version types that implement the org.hibernate.usertype.UserVersionType.

This feature is only available in HQL since it’s not standardized by Jakarta Persistence.

Example 493. A JPQL DELETE statement
int deletedEntities = entityManager.createQuery(
	"delete Person p " +
	"where p.name = :name")
.setParameter("name", name)
.executeUpdate();
Example 494. An HQL DELETE statement
int deletedEntities = session.createMutationQuery(
	"delete Person " +
	"where name = :name")
.setParameter("name", name)
.executeUpdate();

Method Query.executeUpdate() returns an int value, which indicates the number of entities affected by the operation. This may or may not correlate to the number of rows affected in the database. A JPQL/HQL bulk operation might result in multiple SQL statements being executed, such as for joined-subclass. In the example of joined-subclass, a DELETE against one of the subclasses may actually result in deletes in the tables underlying the join, or further down the inheritance hierarchy.

13.3.2. HQL syntax for INSERT

Example 495. Pseudo-syntax for INSERT-SELECT statements
INSERT INTO EntityName
	properties_list
SELECT select_list
FROM ...

Alternatively one can also declare individual values

Example 496. Pseudo-syntax for INSERT-VALUES statements
INSERT INTO EntityName
	properties_list
VALUES values_list

The properties_list is analogous to the column specification in the SQL INSERT statement. Note that INSERT statements are inherently non-polymorphic, so it is not possible to use an EntityName which is abstract or refer to subclass properties.

The SELECT statement can be any valid HQL select query, but the return types must match the types expected by the INSERT. Hibernate verifies the return types during query compilation, instead of expecting the database to check it. Problems might result from Hibernate types which are equivalent, rather than equal. One such example is a mismatch between a property defined as an org.hibernate.type.StandardBasicTypes.DATE and a property defined as an org.hibernate.type.StandardBasicTypes.TIMESTAMP, even though the database may not make a distinction, or may be capable of handling the conversion.

If id property is not specified in the properties_list, Hibernate generates a value automatically. Automatic generation is only available if you use ID generators which operate on the database. Otherwise, Hibernate throws an exception during parsing. Available in-database generators implement org.hibernate.id.PostInsertIdentifierGenerator.

For properties mapped as either version or timestamp, the insert statement gives you two options. You can either specify the property in the properties_list, in which case its value is taken from the corresponding select expressions or omit it from the properties_list, in which case the seed value defined by the org.hibernate.type.descriptor.java.VersionJavaType is used.

Example 497. HQL INSERT statement
int insertedEntities = session.createMutationQuery(
	"insert into Partner (id, name) " +
	"select p.id, p.name " +
	"from Person p ")
.executeUpdate();

This section is only a brief overview of HQL. For more information, see Hibernate Query Language.

13.3.3. Bulk mutation strategies

When a bulk mutation involves multiple tables, Hibernate has to issue individual DML statements to the respective tables. Since the mutation itself could have an effect on the conditions used in the statement, it’s generally not possible to simply execute parts of the DML statement against the respective tables. Instead, Hibernate has to temporarily remember which rows will be affected, and execute the DML statements based on these rows.

Usually, Hibernate will make use of local or global temporary tables to remember the primary keys of the rows. For some databases, currently only PostgreSQL and DB2, a more advanced strategy (CteMutationStrategy) is used, which makes use of DML in CTE support to execute the whole operation in one SQL statement.

The chosen strategy, unless overridden through the hibernate.query.mutation_strategy setting, is based on the Dialect support through org.hibernate.dialect.Dialect.getFallbackSqmMutationStrategy.

Class diagram

Considering we have the following entities:

Entity class diagram

The Person entity is the base class of this entity inheritance model, and is mapped as follows:

Example 498. Bulk mutation base class entity
@Entity(name = "Person")
@Inheritance(strategy = InheritanceType.JOINED)
public static class Person implements Serializable {

	@Id
	private Integer id;

	@Id
	private String companyName;

	private String name;

	private boolean employed;

	//Getters and setters are omitted for brevity

}

Both the Doctor and Engineer entity classes extend the Person base class:

Example 499. Bulk mutation subclass entities
@Entity(name = "Doctor")
public static class Doctor extends Person {
}

@Entity(name = "Engineer")
public static class Engineer extends Person {

	private boolean fellow;

	public boolean isFellow() {
		return fellow;
	}

	public void setFellow(boolean fellow) {
		this.fellow = fellow;
	}
}
Inheritance tree bulk processing

Now, when you try to execute a bulk entity delete query:

Example 500. Bulk mutation delete query example
int updateCount = session.createQuery(
	"delete from Person where employed = :employed" )
.setParameter( "employed", false )
.executeUpdate();
create temporary table
    HT_Person
(
    id int4 not null,
    companyName varchar(255) not null
)

insert
into
    HT_Person
    select
        p.id as id,
        p.companyName as companyName
    from
        Person p
    where
        p.employed = ?

delete
from
    Engineer
where
    (
        id, companyName
    ) IN (
        select
            id,
            companyName
        from
            HT_Person
    )

delete
from
    Doctor
where
    (
        id, companyName
    ) IN (
        select
            id,
            companyName
        from
            HT_Person
    )

delete
from
    Person
where
    (
        id, companyName
    ) IN (
        select
            id,
            companyName
        from
            HT_Person
    )

HT_Person is a temporary table that Hibernate creates to hold all the entity identifiers that are to be updated or deleted by the bulk operation. The temporary table can be either global or local, depending on the underlying database capabilities.

Non-temporary table bulk mutation strategies

The strategies outlined above depend on the creation of temporary tables, which Hibernate creates on startup if they don’t already exist. At present this process is not integrated in the schema management tooling, and this requires that the user have the required permissions to alter the database schema.

If the Hibernate session user lacks these permissions, you will need to either:

  • alter your schema through a different user with more permissions, to add a global temporary table named HTE_<root entity table name>, which contains all columns of all tables involved in the entity hierarchy.
    This will allow insert, update and delete in HQL for multi-table entities.

  • OR configure Hibernate ORM to use the (badly-performing) inline strategy (for mutations only!):

<property name="hibernate.query.mutation_strategy"
          value="org.hibernate.query.sqm.mutation.internal.inline.InlineMutationStrategy"
/>

We strongly recommend the use of the first option, i.e. manually adding the temporary tables, because the inline strategy is set to be removed in a future release. Also, there is no equivalent strategy for inserts.

Additionally, automatic creation of temporary tables should be deactivated. This is done by setting the

hibernate.query.mutation_strategy.global_temporary.create_tables and hibernate.query.mutation_strategy.global_temporary.drop_tables

or

hibernate.query.mutation_strategy.persistent.create_tables and hibernate.query.mutation_strategy.persistent.drop_tables

properties (depending on the default strategy for the dialect) to false

With the inline strategy, when running the previous test case, Hibernate generates the following SQL statements:

Example 501. InlineIdsInClauseBulkIdStrategy delete entity query example
select
    p.id as id,
    p.companyName as companyName
from
    Person p
where
    p.employed = ?

delete
from
    Engineer
where
        ( id, companyName )
    in (
        ( 1,'Red Hat USA' ),
        ( 3,'Red Hat USA' ),
        ( 1,'Red Hat Europe' ),
        ( 3,'Red Hat Europe' )
    )

delete
from
    Doctor
where
        ( id, companyName )
    in (
        ( 1,'Red Hat USA' ),
        ( 3,'Red Hat USA' ),
        ( 1,'Red Hat Europe' ),
        ( 3,'Red Hat Europe' )
    )

delete
from
    Person
where
        ( id, companyName )
    in (
        ( 1,'Red Hat USA' ),
        ( 3,'Red Hat USA' ),
        ( 1,'Red Hat Europe' ),
        ( 3,'Red Hat Europe' )
    )

So, the entity identifiers are selected first and used for each particular update or delete statement.

14. Caching

At runtime, Hibernate handles moving data into and out of the second-level cache in response to the operations performed by the Session, which acts as a transaction-level cache of persistent data. Once an entity becomes managed, that object is added to the internal cache of the current persistence context (EntityManager or Session). The persistence context is also called the first-level cache, and it’s enabled by default.

It is possible to configure a JVM-level (SessionFactory-level) or even a cluster cache on a class-by-class and collection-by-collection basis.

Be aware that Hibernate caches are not aware of changes made to the persistent store by other applications.

To address this limitation, you can configure a TTL (Time To Live) retention policy at the second-level cache region level so that the underlying cache entries expire regularly.

14.1. Configuring second-level caching

Hibernate can integrate with various caching providers for the purpose of caching data outside the context of a particular Session. This section defines the settings which control this behavior.

14.1.1. RegionFactory

org.hibernate.cache.spi.RegionFactory defines the integration between Hibernate and a pluggable caching provider. hibernate.cache.region.factory_class is used to declare the provider to use. Hibernate comes with built-in support for the Java caching standard JCache and also the popular caching library: Infinispan. Detailed information is provided later in this chapter.

14.1.2. Caching configuration properties

Besides provider specific configuration, there are a number of configurations options on the Hibernate side of the integration that control various caching behaviors:

hibernate.cache.use_second_level_cache

Enable or disable second level caching overall. By default, if the currently configured RegionFactory is not the NoCachingRegionFactory, then the second-level cache is going to be enabled. Otherwise, the second-level cache is disabled.

hibernate.cache.use_query_cache

Enable or disable second level caching of query results. The default is false.

hibernate.cache.query_cache_factory

Query result caching is handled by a special contract that deals with staleness-based invalidation of the results. The default implementation does not allow stale results at all. Use this for applications that would like to relax that. Names an implementation of org.hibernate.cache.spi.TimestampsCacheFactory.

hibernate.cache.use_minimal_puts

Optimizes second-level cache operations to minimize writes, at the cost of more frequent reads. Providers typically set this appropriately.

hibernate.cache.region_prefix

Defines a name to be used as a prefix to all second-level cache region names.

hibernate.cache.default_cache_concurrency_strategy

In Hibernate second-level caching, all regions can be configured differently including the concurrency strategy to use when accessing that particular region. This setting allows defining a default strategy to be used. This setting is very rarely required as the pluggable providers do specify the default strategy to use. Valid values include:

  • read-only,

  • read-write,

  • nonstrict-read-write,

  • transactional

hibernate.cache.use_structured_entries

If true, forces Hibernate to store data in the second-level cache in a more human-friendly format. Can be useful if you’d like to be able to "browse" the data directly in your cache, but does have a performance impact.

hibernate.cache.auto_evict_collection_cache

Enables or disables the automatic eviction of a bidirectional association’s collection cache entry when the association is changed just from the owning side. This is disabled by default, as it has a performance impact to track this state. However, if your application does not manage both sides of bidirectional association where the collection side is cached, the alternative is to have stale data in that collection cache.

hibernate.cache.use_reference_entries

Enable direct storage of entity references into the second level cache for read-only or immutable entities.

hibernate.cache.keys_factory

When storing entries into the second-level cache as a key-value pair, the identifiers can be wrapped into tuples <entity type, tenant, identifier> to guarantee uniqueness in case that second-level cache stores all entities in single space. These tuples are then used as keys in the cache. When the second-level cache implementation (incl. its configuration) guarantees that different entity types are stored separately and multi-tenancy is not used, you can omit this wrapping to achieve better performance. Currently, this property is only supported when Infinispan is configured as the second-level cache implementation. Valid values are:

  • default (wraps identifiers in the tuple)

  • simple (uses identifiers as keys without any wrapping)

  • fully qualified class name that implements org.hibernate.cache.spi.CacheKeysFactory

14.2. Configuring second-level cache mappings

The cache mappings can be configured via Jakarta Persistence annotations or XML descriptors or using the Hibernate-specific mapping files.

By default, entities are not part of the second level cache and we recommend you to stick to this setting. However, you can override this by setting the shared-cache-mode element in your persistence.xml file or by using the jakarta.persistence.sharedCache.mode property in your configuration file. The following values are possible:

ENABLE_SELECTIVE (Default and recommended value)

Entities are not cached unless explicitly marked as cacheable (with the @Cacheable annotation).

DISABLE_SELECTIVE

Entities are cached unless explicitly marked as non-cacheable.

ALL

Entities are always cached even if marked as non-cacheable.

NONE

No entity is cached even if marked as cacheable. This option can make sense to disable second-level cache altogether.

The cache concurrency strategy used by default can be set globally via the hibernate.cache.default_cache_concurrency_strategy configuration property. The values for this property are:

read-only

If your application needs to read, but not modify, instances of a persistent class, a read-only cache is the best choice. Application can still delete entities and these changes should be reflected in second-level cache so that the cache does not provide stale entities. Implementations may use performance optimizations based on the immutability of entities.

read-write

If the application needs to update data, a read-write cache might be appropriate. This strategy provides consistent access to single entity, but not a serializable transaction isolation level; e.g. when TX1 reads looks up an entity and does not find it, TX2 inserts the entity into cache and TX1 looks it up again, the new entity can be read in TX1.

nonstrict-read-write

Similar to read-write strategy but there might be occasional stale reads upon concurrent access to an entity. The choice of this strategy might be appropriate if the application rarely updates the same data simultaneously and strict transaction isolation is not required. Implementations may use performance optimizations that make use of the relaxed consistency guarantee.

transactional

Provides serializable transaction isolation level.

Rather than using a global setting, it is recommended to define the cache concurrency strategy on a per entity basis.

Use the @org.hibernate.annotations.Cache annotation for this purpose.

The @Cache annotation define three attributes:

usage

Defines the CacheConcurrencyStrategy

region

Defines a cache region where entries will be stored

include

If lazy properties should be included in the second level cache. The default value is all so lazy properties are cacheable. The other possible value is non-lazy so lazy properties are not cacheable.

14.3. Entity inheritance and second-level cache mapping

Traditionally, when using entity inheritance, Hibernate required an entity hierarchy to be either cached entirely or not cached at all. Therefore, if you wanted to cache a subclass belonging to a given entity hierarchy, the Jakarta Persistence @Cacheable and the Hibernate-specific @Cache annotations would have to be declared at the root-entity level only.

Although we still believe that all entities belonging to a given entity hierarchy should share the same caching semantics, the Jakarta Persistence specification says that the @Cacheable annotation could be overwritten by a subclass:

The value of the Cacheable annotation is inherited by subclasses; it can be overridden by specifying Cacheable on a subclass.

— Section 11.1.7 of the Jakarta Persistence

As of Hibernate ORM 5.3, you can now override a base class @Cacheable or @Cache definition at subclass level.

However, the Hibernate cache concurrency strategy (e.g. read-only, nonstrict-read-write, read-write, transactional) is still defined at the root entity level and cannot be overridden.

Nevertheless, the reasons why we advise you to have all entities belonging to an inheritance tree share the same caching definition can be summed as follows:

  • from a performance perspective, adding an additional check on a per entity type level slows the bootstrap process.

  • providing different caching semantics for subclasses would violate the Liskov substitution principle.

14.4. Entity cache

Example 502. Entity cache mapping
@Entity(name = "Phone")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public static class Phone {

	@Id
	@GeneratedValue
	private Long id;

	private String mobile;

	@ManyToOne
	private Person person;

	@Version
	private int version;

	//Getters and setters are omitted for brevity

}

Hibernate stores cached entities in a dehydrated form, which is similar to the database representation. Aside from the foreign key column values of the @ManyToOne or @OneToOne child-side associations, entity relationships are not stored in the cache,

Once an entity is stored in the second-level cache, you can avoid a database hit and load the entity from the cache alone:

Example 503. Loading entity using Jakarta Persistence
Person person = entityManager.find(Person.class, 1L);
Example 504. Loading entity using Hibernate native API
Person person = session.get(Person.class, 1L);

The Hibernate second-level cache can also load entities by their natural id:

Example 505. Hibernate natural id entity mapping
@Entity(name = "Person")
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public static class Person {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long id;

	private String name;

	@NaturalId
	@Column(name = "code", unique = true)
	private String code;

	//Getters and setters are omitted for brevity

}
Example 506. Loading entity using Hibernate native natural id API
Person person = session
	.byNaturalId(Person.class)
	.using("code", "unique-code")
	.load();

14.5. Collection cache

Hibernate can also cache collections, and the @Cache annotation must be on added to the collection property.

If the collection is made of value types (basic or embeddables mapped with @ElementCollection), the collection is stored as such. If the collection contains other entities (@OneToMany or @ManyToMany), the collection cache entry will store the entity identifiers only.

Example 507. Collection cache mapping
@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
private List<Phone> phones = new ArrayList<>();

Collections are read-through, meaning they are cached upon being accessed for the first time:

Example 508. Collection cache usage
Person person = entityManager.find(Person.class, 1L);
person.getPhones().size();

Subsequent collection retrievals will use the cache instead of going to the database.

The collection cache is not write-through so any modification will trigger a collection cache entry invalidation. On a subsequent access, the collection will be loaded from the database and re-cached.

14.6. Query cache

Aside from caching entities and collections, Hibernate offers a query cache too. This is useful for frequently executed queries with fixed parameter values.

Caching of query results introduces some overhead in terms of your applications normal transactional processing. For example, if you cache results of a query against Person, Hibernate will need to keep track of when those results should be invalidated because changes have been committed against any Person entity.

That, coupled with the fact that most applications simply gain no benefit from caching query results, leads Hibernate to disable caching of query results by default.

To use query caching, you will first need to enable it with the following configuration property:

Example 509. Enabling query cache
<property
    name="hibernate.cache.use_query_cache"
    value="true" />

As mentioned above, most queries do not benefit from caching or their results. So by default, individual queries are not cached even after enabling query caching. Each particular query that needs to be cached must be manually set as cacheable. This way, the query looks for existing cache results or adds the query results to the cache when being executed.

Example 510. Caching query using Jakarta Persistence
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name = :name", Person.class)
.setParameter("name", "John Doe")
.setHint("org.hibernate.cacheable", "true")
.getResultList();
Example 511. Caching query using Hibernate native API
List<Person> persons = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.name = :name", Person.class)
.setParameter("name", "John Doe")
.setCacheable(true)
.list();

For entity queries, the query cache does not cache the state of the actual entities. Instead, it stores the entity identifiers, and when the query result is fetched from the cache, the entity state is going to be loaded from the second-level cache entity regions.

Just as with collection caching, the query cache should always be used in conjunction with the second-level cache for those entities expected to be cached as part of a query result cache.

For projection queries, the query cache stores the dehydrated entity state (e.g. Object[]) associated with the underlying JDBC ResultSet.

14.6.1. Query cache regions

This setting creates two new cache regions:

default-query-results-region

Holding the cached query results.

default-update-timestamps-region

Holding timestamps of the most recent updates to queryable tables. These are used to validate the results as they are served from the query cache.

If you configure your underlying cache implementation to use expiration, it’s very important that the timeout of the underlying cache region for the default-update-timestamps-region is set to a higher value than the timeout setting of any of the query caches.

In fact, we recommend that the default-update-timestamps-region region is not configured for expiration (time-based) or eviction (size/memory-based) at all. Note that an LRU (Least Recently Used) cache eviction policy is never appropriate for this particular cache region.

If you require fine-grained control over query cache expiration policies, you can specify a named cache region for a particular query.

Example 512. Caching query in custom region using Jakarta Persistence
List<Person> persons = entityManager.createQuery(
		"select p " +
		"from Person p " +
		"where p.id > :id", Person.class)
		.setParameter("id", 0L)
		.setHint(HINT_CACHEABLE, "true")
		.setHint(HINT_CACHE_REGION, "query.cache.person")
		.getResultList();
Example 513. Caching query in custom region using Hibernate native API
List<Person> persons = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setCacheable(true)
.setCacheRegion("query.cache.person")
.list();

If you want to force the query cache to refresh one of its regions (disregarding any cached results it finds there), you can use custom cache modes.

Example 514. Using custom query cache mode with Jakarta Persistence
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setHint(HINT_CACHEABLE, "true")
.setHint(HINT_CACHE_REGION, "query.cache.person")
.setHint("jakarta.persistence.cache.storeMode", CacheStoreMode.REFRESH)
.getResultList();
Example 515. Using custom query cache mode with Hibernate native API
List<Person> persons = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.id > :id", Person.class)
.setParameter("id", 0L)
.setCacheable(true)
.setCacheRegion("query.cache.person")
.setCacheMode(CacheMode.REFRESH)
.list();

When using CacheStoreMode.REFRESH or CacheMode.REFRESH in conjunction with the region you have defined for the given query, Hibernate will selectively force the results cached in that particular region to be refreshed.

This behavior is particularly useful in cases when the underlying data may have been updated via a separate process and is a far more efficient alternative to the bulk eviction of the region via SessionFactory eviction which looks as follows:

session.getSessionFactory().getCache().evictQueryRegion("query.cache.person");

14.7. Managing the cached data

Traditionally, Hibernate defined the CacheMode enumeration to describe the ways of interactions with the cached data. Jakarta Persistence split cache modes by storage (CacheStoreMode) and retrieval (CacheRetrieveMode).

The relationship between Hibernate and Jakarta Persistence cache modes can be seen in the following table:

Table 2. Cache modes relationships
Hibernate Jakarta Persistence Description

CacheMode.NORMAL

CacheStoreMode.USE and CacheRetrieveMode.USE

Default. Reads/writes data from/into the cache

CacheMode.REFRESH

CacheStoreMode.REFRESH and CacheRetrieveMode.BYPASS

Doesn’t read from cache, but writes to the cache upon loading from the database

CacheMode.PUT

CacheStoreMode.USE and CacheRetrieveMode.BYPASS

Doesn’t read from cache, but writes to the cache as it reads from the database

CacheMode.GET

CacheStoreMode.BYPASS and CacheRetrieveMode.USE

Read from the cache, but doesn’t write to cache

CacheMode.IGNORE

CacheStoreMode.BYPASS and CacheRetrieveMode.BYPASS

Doesn’t read/write data from/into the cache

Setting the cache mode can be done either when loading entities directly or when executing a query.

Example 516. Using custom cache modes with Jakarta Persistence
Map<String, Object> hints = new HashMap<>();
hints.put("jakarta.persistence.cache.retrieveMode" , CacheRetrieveMode.USE);
hints.put("jakarta.persistence.cache.storeMode" , CacheStoreMode.REFRESH);
Person person = entityManager.find(Person.class, 1L , hints);
Example 517. Using custom cache modes with Hibernate native API
session.setCacheMode(CacheMode.REFRESH);
Person person = session.get(Person.class, 1L);

The custom cache modes can be set for queries as well:

Example 518. Using custom cache modes for queries with Jakarta Persistence
List<Person> persons = entityManager.createQuery(
	"select p from Person p", Person.class)
.setHint(HINT_CACHEABLE, "true")
.setHint("jakarta.persistence.cache.retrieveMode" , CacheRetrieveMode.USE)
.setHint("jakarta.persistence.cache.storeMode" , CacheStoreMode.REFRESH)
.getResultList();
Example 519. Using custom cache modes for queries with Hibernate native API
List<Person> persons = session.createQuery(
	"select p from Person p", Person.class)
.setCacheable(true)
.setCacheMode(CacheMode.REFRESH)
.list();

14.7.1. Evicting cache entries

Because the second level cache is bound to the EntityManagerFactory or the SessionFactory, cache eviction must be done through these two interfaces.

Jakarta Persistence only supports entity eviction through the jakarta.persistence.Cache interface:

Example 520. Evicting entities with Jakarta Persistence
entityManager.getEntityManagerFactory().getCache().evict(Person.class);

Hibernate is much more flexible in this regard as it offers fine-grained control over what needs to be evicted. The org.hibernate.Cache interface defines various evicting strategies:

  • entities (by their class or region)

  • entities stored using the natural-id (by their class or region)

  • collections (by the region, and it might take the collection owner identifier as well)

  • queries (by region)

Example 521. Evicting entities with Hibernate native API
session.getSessionFactory().getCache().evictQueryRegion("query.cache.person");

14.8. Caching statistics

If you enable the hibernate.generate_statistics configuration property, Hibernate will expose a number of metrics via SessionFactory.getStatistics(). Hibernate can even be configured to expose these statistics via JMX.

This way, you can get access to the Statistics class which comprises all sort of second-level cache metrics.

Example 522. Caching statistics
Statistics statistics = session.getSessionFactory().getStatistics();
CacheRegionStatistics secondLevelCacheStatistics =
		statistics.getDomainDataRegionStatistics("query.cache.person");
long hitCount = secondLevelCacheStatistics.getHitCount();
long missCount = secondLevelCacheStatistics.getMissCount();
double hitRatio = (double) hitCount / (hitCount + missCount);

14.9. JCache

To use the built-in integration for JCache, you need the hibernate-jcache module jar (and all of its dependencies) to be on the classpath.

In addition, a JCache implementation needs to be added as well. A list of compatible implementations can be found on the JCP website. An alternative source of compatible implementations can be found through the JSR-107 test zoo.

14.9.1. RegionFactory

The hibernate-jcache module defines the following region factory: JCacheRegionFactory.

To use the JCacheRegionFactory, you need to specify the following configuration property:

Example 523. JCacheRegionFactory configuration
<property
    name="hibernate.cache.region.factory_class"
    value="jcache"/>

The JCacheRegionFactory configures a javax.cache.CacheManager.

14.9.2. JCache CacheManager

JCache mandates that CacheManagers sharing the same URI and class loader be unique in JVM.

If you do not specify additional properties, the JCacheRegionFactory will load the default JCache provider and create the default CacheManager. Also, Caches will be created using the default javax.cache.configuration.MutableConfiguration.

In order to control which provider to use and specify configuration for the CacheManager and Caches you can use the following two properties:

Example 524. JCache configuration
<property
    name="hibernate.javax.cache.provider"
    value="org.ehcache.jsr107.EhcacheCachingProvider"/>
<property
    name="hibernate.javax.cache.uri"
    value="file:/path/to/ehcache.xml"/>

Only by specifying the second property hibernate.javax.cache.uri will you be able to have a CacheManager per SessionFactory.

Using a non-default JCache CacheManager

If you don’t want to use the default CacheManager, you need to set the hibernate.javax.cache.cache_manager configuration property to one of the following values:

Object reference

If the value is an Object instance implementing the CacheManager interface, the provided CacheManager instance will be used.

Class

If the value is a Java Class object that implements the CacheManager interface, Hibernate will create a new instance for that Class and use it instead of the default one.

When passing a Java Class that implements the CacheManager interface, you must make sure that the CacheManager implementation class provides a default no-arg constructor because that’s going to be used to instantiate a CacheManager implementation Object.

String

If the value is a Java String, Hibernate expects it to be the fully-qualified Class name of the CacheManager implementation which will be used to instantiate the non-default CacheManager.

When passing the fully-qualified class name, you must make sure that the associated Class type provides a default no-arg constructor because that’s going to be used to instantiate a CacheManager implementation Object.

14.9.3. JCache missing cache strategy

By default, the JCache region factory will log a warning when asked to create a cache that is not explicitly configured and pre-started in the underlying cache manager. Thus if you configure an entity type or a collection as cached, but do not configure the corresponding cache explicitly, one warning will be logged for each cache that was not configured explicitly.

You may change this behavior by setting the hibernate.javax.cache.missing_cache_strategy property to one of the following values:

Table 3. Missing cache strategies
Value Description

fail

Fail with an exception on missing caches.

create-warn

Default value. Create a new cache when a cache is not found (see create below), and also log a warning about the missing cache.

create

Create a new cache when a cache is not found, without logging any warning about the missing cache.

Note that caches created this way may not be suitable for production usage (unlimited size and no eviction in particular) unless the cache provider explicitly provides a specific configuration for default caches.

Recent versions of Ehcache enable disk persistence (<persistence strategy="localTempSwap"/>) for the default cache causing performance degradation, it is highly recommended to define the caches explicitly (see Hibernate Jira issue HHH-14544).

Ehcache, in particular, allows to set such default configuration using cache templates. See the Ehcache documentation for more details.

14.10. Infinispan

Infinispan is a distributed in-memory key/value data store, available as a cache or data grid, which can be used as a Hibernate second-level cache provider as well.

It supports advanced functionality such as transactions, events, querying, distributed processing, off-heap and geographical failover.

For more details, check out the Infinispan User Guide.

15. Interceptors and Events

It is useful for the application to react to certain events that occur inside Hibernate. This allows for the implementation of generic functionality and the extension of Hibernate functionality.

15.1. Interceptors

The org.hibernate.Interceptor interface provides callbacks from the session to the application, allowing the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded.

One possible use for this is to track auditing information. The following example shows an Interceptor implementation that automatically logs when an entity is updated.

public static class LoggingInterceptor implements Interceptor {
	@Override
	public boolean onFlushDirty(
		Object entity,
		Object id,
		Object[] currentState,
		Object[] previousState,
		String[] propertyNames,
		Type[] types) {
			LOGGER.debugv("Entity {0}#{1} changed from {2} to {3}",
				entity.getClass().getSimpleName(),
				id,
				Arrays.toString(previousState),
				Arrays.toString(currentState)
			);
			return Interceptor.super.onFlushDirty(entity, id, currentState,
				previousState, propertyNames, types
		);
	}
}

You can either implement Interceptor directly or extend the org.hibernate.EmptyInterceptor base class.

An Interceptor can be either Session-scoped or SessionFactory-scoped.

A Session-scoped interceptor is specified when a session is opened.

SessionFactory sessionFactory = entityManagerFactory.unwrap(SessionFactory.class);
Session session = sessionFactory
	.withOptions()
	.interceptor(new LoggingInterceptor())
	.openSession();
session.getTransaction().begin();

Customer customer = session.get(Customer.class, customerId);
customer.setName("Mr. John Doe");
//Entity Customer#1 changed from [John Doe, 0] to [Mr. John Doe, 0]

session.getTransaction().commit();

A SessionFactory-scoped interceptor is registered with the Configuration object prior to building the SessionFactory. Unless a session is opened explicitly specifying the interceptor to use, the SessionFactory-scoped interceptor will be applied to all sessions opened from that SessionFactory. SessionFactory-scoped interceptors must be thread-safe. Ensure that you do not store session-specific states since multiple sessions will use this interceptor potentially concurrently.

SessionFactory sessionFactory = new MetadataSources(new StandardServiceRegistryBuilder().build())
	.addAnnotatedClass(Customer.class)
	.getMetadataBuilder()
	.build()
	.getSessionFactoryBuilder()
	.applyInterceptor(new LoggingInterceptor())
	.build();

15.2. Native Event system

If you have to react to particular events in the persistence layer, you can also use the Hibernate event architecture. The event system can be used in place of or in addition to interceptors.

Many methods of the Session interface correlate to an event type. The full range of defined event types is declared as enum values on org.hibernate.event.spi.EventType. When a request is made of one of these methods, the Session generates an appropriate event and passes it to the configured event listener(s) for that type.

Applications can customize the listener interfaces (i.e., the LoadEvent is processed by the registered implementation of the LoadEventListener interface), in which case their implementations would be responsible for processing the load() requests made of the Session.

The listeners should be considered stateless. They are shared between requests, and should not save any state as instance variables.

A custom listener implements the appropriate interface for the event it wants to process and/or extend one of the convenience base classes (or even the default event listeners used by Hibernate out-of-the-box as these are declared non-final for this purpose).

Here is an example of a custom load event listener:

Example 525. Custom LoadListener example
EntityManagerFactory entityManagerFactory = entityManagerFactory();
SessionFactoryImplementor sessionFactory = entityManagerFactory.unwrap( SessionFactoryImplementor.class );
sessionFactory
	.getServiceRegistry()
	.getService( EventListenerRegistry.class )
	.prependListeners( EventType.LOAD, new SecuredLoadEntityListener() );

Customer customer = entityManager.find( Customer.class, customerId );
public static class SecuredLoadEntityListener implements LoadEventListener {
	// this is the single method defined by the LoadEventListener interface
	public void onLoad(LoadEvent event, LoadType loadType)
			throws HibernateException {
		if ( !Principal.isAuthorized( event.getEntityClassName(), event.getEntityId() ) ) {
			throw new SecurityException( "Unauthorized access" );
		}
	}
}

15.3. Mixing Events and Interceptors

When you want to customize the entity state transition behavior, you have two options:

  1. you provide a custom Interceptor, which is taken into consideration by the default Hibernate event listeners. For example, the Interceptor#onSave() method is invoked by Hibernate AbstractSaveEventListener. Or, the Interceptor#onLoad() is called by the DefaultPreLoadEventListener.

  2. you can replace any given default event listener with your own implementation. When doing this, you should probably extend the default listeners because otherwise, you’d have to take care of all the low-level entity state transition logic. For example, if you replace the DefaultPreLoadEventListener with your own implementation, then, only if you call the Interceptor#onLoad() method explicitly, you can mix the custom load event listener with a custom Hibernate interceptor.

15.4. Jakarta Persistence Callbacks

Jakarta Persistence also defines a more limited set of callbacks through annotations.

Table 4. Callback annotations
Type Description

@PrePersist

Executed before the entity manager persist operation is actually executed or cascaded. This call is synchronous with the persist operation.

@PreRemove

Executed before the entity manager remove operation is actually executed or cascaded. This call is synchronous with the remove operation.

@PostPersist

Executed after the entity manager persist operation is actually executed or cascaded. This call is invoked after the database INSERT is executed.

@PostRemove

Executed after the entity manager remove operation is actually executed or cascaded. This call is synchronous with the remove operation.

@PreUpdate

Executed before the database UPDATE operation.

@PostUpdate

Executed after the database UPDATE operation.

@PostLoad

Executed after an entity has been loaded into the current persistence context or an entity has been refreshed.

There are two available approaches defined for specifying callback handling:

  • The first approach is to annotate methods on the entity itself to receive notifications of a particular entity lifecycle event(s).

  • The second is to use a separate entity listener class. An entity listener is a stateless class with a no-arg constructor. The callback annotations are placed on a method of this class instead of the entity class. The entity listener class is then associated with the entity using the jakarta.persistence.EntityListeners annotation

Example 526. Example of specifying Jakarta Persistence callbacks
@Entity(name = "Person")
@EntityListeners( LastUpdateListener.class )
public static class Person {

	@Id
	private Long id;

	private String name;

	private Date dateOfBirth;

	@Transient
	private long age;

	private Date lastUpdate;

	public void setLastUpdate(Date lastUpdate) {
		this.lastUpdate = lastUpdate;
	}

	/**
	 * Set the transient property at load time based on a calculation.
	 * Note that a native Hibernate formula mapping is better for this purpose.
	 */
	@PostLoad
	public void calculateAge() {
		age = ChronoUnit.YEARS.between( LocalDateTime.ofInstant(
				Instant.ofEpochMilli( dateOfBirth.getTime()), ZoneOffset.UTC),
			LocalDateTime.now()
		);
	}
}

public static class LastUpdateListener {

	@PreUpdate
	@PrePersist
	public void setLastUpdate( Person p ) {
		p.setLastUpdate( new Date() );
	}
}

These approaches can be mixed, meaning you can use both together.

Regardless of whether the callback method is defined on the entity or on an entity listener, it must have a void-return signature. The name of the method is irrelevant as it is the placement of the callback annotations that makes the method a callback. In the case of callback methods defined on the entity class, the method must additionally have a no-argument signature. For callback methods defined on an entity listener class, the method must have a single argument signature; the type of that argument can be either java.lang.Object (to facilitate attachment to multiple entities) or the specific entity type.

A callback method can throw a RuntimeException. If the callback method does throw a RuntimeException, then the current transaction, if any, must be rolled back.

A callback method must not invoke EntityManager or Query methods!

It is possible that multiple callback methods are defined for a particular lifecycle event. When that is the case, the defined order of execution is well defined by the Jakarta Persistence spec (specifically section 3.5.4):

  • Any default listeners associated with the entity are invoked first, in the order they were specified in the XML. See the jakarta.persistence.ExcludeDefaultListeners annotation.

  • Next, entity listener class callbacks associated with the entity hierarchy are invoked, in the order they are defined in the EntityListeners. If multiple classes in the entity hierarchy define entity listeners, the listeners defined for a superclass are invoked before the listeners defined for its subclasses. See the jakarta.persistence.ExcludeSuperclassListener's annotation.

  • Lastly, callback methods defined on the entity hierarchy are invoked. If a callback type is annotated on both an entity and one or more of its superclasses without method overriding, both would be called, the most general superclass first. An entity class is also allowed to override a callback method defined in a superclass in which case the super callback would not get invoked; the overriding method would get invoked provided it is annotated.

15.5. Default entity listeners

The Jakarta Persistence specification allows you to define a default entity listener which is going to be applied for every entity in that particular system. Default entity listeners can only be defined in XML mapping files.

Example 527. Default event listener mapping
public class DefaultEntityListener {

    public void onPersist(Object entity) {
        if (entity instanceof BaseEntity) {
            BaseEntity baseEntity = (BaseEntity) entity;
            baseEntity.setCreatedOn(now());
        }
    }

    public void onUpdate(Object entity) {
        if (entity instanceof BaseEntity) {
            BaseEntity baseEntity = (BaseEntity) entity;
            baseEntity.setUpdatedOn(now());
        }
    }

    private Timestamp now() {
        return Timestamp.from(
            LocalDateTime.now().toInstant(ZoneOffset.UTC)
       );
    }
}
<entity-mappings xmlns="http://xmlns.jcp.org/xml/ns/persistence/orm"
                 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence/orm
                 http://xmlns.jcp.org/xml/ns/persistence/orm_2_1.xsd"
                 version="2.1">
    <persistence-unit-metadata>
        <persistence-unit-defaults>
            <entity-listeners>
                <entity-listener
                    class="org.hibernate.orm.test.events.DefaultEntityListener">
                    <pre-persist method-name="onPersist"/>
                    <pre-update method-name="onUpdate"/>
                </entity-listener>
            </entity-listeners>
        </persistence-unit-defaults>
    </persistence-unit-metadata>
</entity-mappings>

Considering that all entities extend the BaseEntity class:

@MappedSuperclass
public abstract class BaseEntity {

    private Timestamp createdOn;

    private Timestamp updatedOn;

    //Getters and setters are omitted for brevity

}
@Entity(name = "Person")
public static class Person extends BaseEntity {

	@Id
	private Long id;

	private String name;

	//Getters and setters omitted for brevity
}

@Entity(name = "Book")
public static class Book extends BaseEntity {

	@Id
	private Long id;

	private String title;

	@ManyToOne
	private Person author;

	//Getters and setters omitted for brevity
}

When persisting a Person or Book entity, the createdOn is going to be set by the onPersist method of the DefaultEntityListener.

Example 528. Default event listener persist event
Person author = new Person();
author.setId(1L);
author.setName("Vlad Mihalcea");

entityManager.persist(author);

Book book = new Book();
book.setId(1L);
book.setTitle("High-Performance Java Persistence");
book.setAuthor(author);

entityManager.persist(book);
insert
into
    Person
    (createdOn, updatedOn, name, id)
values
    (?, ?, ?, ?)

-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.224]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR]   - [Vlad Mihalcea]
-- binding parameter [4] as [BIGINT]    - [1]

insert
into
    Book
    (createdOn, updatedOn, author_id, title, id)
values
    (?, ?, ?, ?, ?)

-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.246]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [BIGINT]    - [1]
-- binding parameter [4] as [VARCHAR]   - [High-Performance Java Persistence]
-- binding parameter [5] as [BIGINT]    - [1]

When updating a Person or Book entity, the updatedOn is going to be set by the onUpdate method of the DefaultEntityListener.

Example 529. Default event listener update event
Person author = entityManager.find(Person.class, 1L);
author.setName("Vlad-Alexandru Mihalcea");

Book book = entityManager.find(Book.class, 1L);
book.setTitle("High-Performance Java Persistence 2nd Edition");
update
    Person
set
    createdOn=?,
    updatedOn=?,
    name=?
where
    id=?

-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.224]
-- binding parameter [2] as [TIMESTAMP] - [2017-06-08 19:23:48.316]
-- binding parameter [3] as [VARCHAR]   - [Vlad-Alexandru Mihalcea]
-- binding parameter [4] as [BIGINT]    - [1]

update
    Book
set
    createdOn=?,
    updatedOn=?,
    author_id=?,
    title=?
where
    id=?

-- binding parameter [1] as [TIMESTAMP] - [2017-06-08 19:23:48.246]
-- binding parameter [2] as [TIMESTAMP] - [2017-06-08 19:23:48.317]
-- binding parameter [3] as [BIGINT]    - [1]
-- binding parameter [4] as [VARCHAR]   - [High-Performance Java Persistence 2nd Edition]
-- binding parameter [5] as [BIGINT]    - [1]

15.5.1. Exclude default entity listeners

If you already registered a default entity listener, but you don’t want to apply it to a particular entity, you can use the @ExcludeDefaultListeners and @ExcludeSuperclassListeners Jakarta Persistence annotations.

@ExcludeDefaultListeners instructs the current class to ignore the default entity listeners for the current entity while @ExcludeSuperclassListeners is used to ignore the default entity listeners propagated to the BaseEntity super-class.

Example 530. Exclude default event listener mapping
@Entity(name = "Publisher")
@ExcludeDefaultListeners
@ExcludeSuperclassListeners
public static class Publisher extends BaseEntity {

	@Id
	private Long id;

	private String name;

	//Getters and setters omitted for brevity
}

When persisting a Publisher entity, the createdOn is not going to be set by the onPersist method of the DefaultEntityListener because the Publisher entity was marked with the @ExcludeDefaultListeners and @ExcludeSuperclassListeners annotations.

Example 531. Excluding default event listener events
Publisher publisher = new Publisher();
publisher.setId(1L);
publisher.setName("Amazon");

entityManager.persist(publisher);
insert
into
    Publisher
    (createdOn, updatedOn, name, id)
values
    (?, ?, ?, ?)

-- binding parameter [1] as [TIMESTAMP] - [null]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR]   - [Amazon]
-- binding parameter [4] as [BIGINT]    - [1]

16. Java API for HQL and JPQL

The Hibernate Query Language (HQL) and the Java Persistence Query Language (JPQL) are object-oriented query languages based on SQL and very similar in flavor to SQL.

When we use the term "HQL" here, we usually mean both modern HQL, along with the standard subset defined by the specification.

HQL is not the only way to write queries in Hibernate:

However, HQL is the most convenient option for most people most of the time.

The actual query language itself is discussed the next chapter. This chapter describes the Java APIs for executing HQL and JPQL queries.

Most of this chapter is dedicated to discussing org.hibernate.query.Query, jakarta.persistence.Query and jakarta.persistence.TypedQuery. These Query contracts mix the ability to perform selections as well mutations. Hibernate additionally offers the more targeted SelectionQuery and MutationQuery contracts. See SelectionQuery and MutationQuery for additional details.

16.1. Example domain model

The code examples featured in this chapter, and the next, make use of the following annotated domain model.

Example 532. Examples domain model
@NamedQuery(
		name = "get_person_by_name",
		query = "select p from Person p where name = :name"
)
@NamedQuery(
		name = "get_read_only_person_by_name",
		query = "select p from Person p where name = :name",
		hints = {
				@QueryHint(
						name = "org.hibernate.readOnly",
						value = "true"
				)
		}
)
@NamedQuery(
		name = "delete_person",
		query = "delete Person"
)
@NamedStoredProcedureQuery(
		name = "sp_person_phones",
		procedureName = "sp_person_phones",
		parameters = {
				@StoredProcedureParameter(
						name = "personId",
						type = Long.class,
						mode = ParameterMode.IN
				),
				@StoredProcedureParameter(
						name = "personPhones",
						type = Class.class,
						mode = ParameterMode.REF_CURSOR
				)
		}
)
@Entity
public class Person {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	private String nickName;

	private String address;

	private LocalDateTime createdOn;

	@OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
	@OrderColumn(name = "order_id")
	private List<Phone> phones = new ArrayList<>();

	@ElementCollection
	@MapKeyEnumerated(EnumType.STRING)
	private Map<AddressType, String> addresses = new HashMap<>();

	@Version
	private int version;

	//Getters and setters are omitted for brevity

}

public enum AddressType {
	HOME,
	OFFICE
}

@Entity
public class Partner {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	@Version
	private int version;

	//Getters and setters are omitted for brevity

}

@Entity
public class Phone {

	@Id
	private Long id;

	@ManyToOne(fetch = FetchType.LAZY)
	private Person person;

	@Column(name = "phone_number")
	private String number;

	@Enumerated(EnumType.STRING)
	@Column(name = "phone_type")
	private PhoneType type;

	@OneToMany(mappedBy = "phone", cascade = CascadeType.ALL, orphanRemoval = true)
	private List<Call> calls = new ArrayList<>(  );

	@OneToMany(mappedBy = "phone")
	@MapKey(name = "timestamp")
	private Map<LocalDateTime, Call> callHistory = new HashMap<>();

	@ElementCollection
	private List<LocalDateTime> repairTimestamps = new ArrayList<>(  );

	//Getters and setters are omitted for brevity

}

public enum PhoneType {
	LAND_LINE,
	MOBILE;
}

@Entity
@Table(name = "phone_call")
public class Call {

	@Id
	@GeneratedValue
	private Long id;

	@ManyToOne
	private Phone phone;

	@Column(name = "call_timestamp")
	private LocalDateTime timestamp;

	private int duration;

	@ManyToOne
	private Payment payment;

	//Getters and setters are omitted for brevity

}

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Payment {

	@Id
	@GeneratedValue
	private Long id;

	private BigDecimal amount;

	private boolean completed;

	@ManyToOne
	private Account account;

	@ManyToOne
	private Person person;

	//Getters and setters are omitted for brevity

}

@Entity
public class CreditCardPayment extends Payment {
	String cardNumber;

	public void setCardNumber(String cardNumber) {
		this.cardNumber = cardNumber;
	}

	public String getCardNumber() {
		return cardNumber;
	}
}

@Entity
public class WireTransferPayment extends Payment {
}

16.2. Obtaining a Query object

A query may be provided to Hibernate as either:

  • an inline query: the text of the query is passed as a string to the session at runtime, or

  • a named query: the query is specified in an annotation or XML file, and identified by name at runtime.

A Query object is obtained from the EntityManager or Hibernate Session by calling createQuery() or createNamedQuery().

The API for actually executing the query is the same in both cases, as we’re about to see below.

16.2.1. Declaring named queries

Named queries may be defined using the Jakarta Persistence annotation @NamedQuery.

Example 533. Declaring a named query with a query hint
@NamedQuery(
		name = "get_read_only_person_by_name",
		query = "select p from Person p where name = :name",
		hints = {
				@QueryHint(
						name = "org.hibernate.readOnly",
						value = "true"
				)
		}
)

Alternatively, Hibernate offers an extended @NamedQuery annotation which allows the specification of additional properties of the query, including flush mode, cacheability, and timeout interval, in a more typesafe way.

Example 534. Declaring a named query using the typesafe annotation
@NamedQuery(
		name = "get_phone_by_number",
		query = "select p " +
				"from Phone p " +
				"where p.number = :number",
		timeout = 1,
		readOnly = true
)

One big advantage to named queries is that they are parsed by Hibernate at startup time, and so some sorts of errors are reported much earlier.

16.2.2. Flavors of the Query API

To execute a query, you’ll need an instance of the Jakarta Persistence Query interface, or, even better, of its subinterface TypedQuery.

Jakarta Persistence Query and TypedQuery

The EntityManager offers various operations that return Query or TypedQuery<T>, including:

  • EntityManager#createQuery(), which accepts a query written in HQL, and

  • EntityManager#createNamedQuery(), which accepts the name of a named query.

It’s better to explicitly pass the query result type as a Java Class<T>. That way, you’ll obtain a TypedQuery<T>, and avoid some later typecasting.

Example 535. Obtaining a Jakarta Persistence Query or TypedQuery reference
Query query = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name"
);

TypedQuery<Person> typedQuery = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class
);
Example 536. Obtaining a Jakarta Persistence Query or TypedQuery reference for a named query
@NamedQuery(
		name = "get_person_by_name",
		query = "select p from Person p where name = :name"
)

Query query = entityManager.createNamedQuery("get_person_by_name");

TypedQuery<Person> typedQuery = entityManager.createNamedQuery("get_person_by_name", Person.class);
Hibernate Query

Hibernate’s Session interface refines the return types of the operations of EntityManager which create query objects.

Session#createQuery(), Session#createNamedQuery(), and other similar operations all return an instance of the extension org.hibernate.query.Query.

Some overloaded forms of these operations return a raw type, but in Hibernate 6 all of these have been deprecated, and the use of the raw type Query is now strongly discouraged. Programs should migrate to the use of the typesafe overloads which accept a Class<T> object and return a typed Query<T>.

Hibernate’s Query interface offers additional operations not available via TypedQuery, as we’ll see below.

Example 537. Obtaining a Hibernate Query
org.hibernate.query.Query<Person> query = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class);
Example 538. Obtaining a Hibernate Query for a named query
org.hibernate.query.Query<Person> query = session.createNamedQuery(
	"get_person_by_name",
	Person.class);

16.3. Executing HQL and JPQL queries

Since org.hibernate.query.Query inherits TypedQuery, which in turn inherits Query, usage of the three interfaces is almost identical.

16.3.1. Binding arguments to query parameters

A query may have named parameters or ordinal parameters:

  • named parameters are specified using the syntax :name, and

  • ordinal parameters are specified using the syntax ?1, ?2, etc.

If the query has parameters, arguments must be bound to each parameter before the query is executed.

Example 539. Named parameter binding
Query query = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name")
.setParameter("name", "J%");

Query query = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.createdOn > :timestamp")
.setParameter("timestamp", timestamp);

JPQL-style ordinal parameters are numbered from 1. Just like with named parameters, a ordinal parameter may appear multiple times in a query.

Example 540. Ordinal parameter binding
TypedQuery<Person> query = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like ?1",
	Person.class)
.setParameter(1, "J%");

It’s not a good idea to mix named and ordinal parameters in a single query.

16.3.2. Executing the query

The Query interface is used to control the execution of the query.

  • Query#getResultList() is useful when the query might return zero, or more than one result.

  • Query#getSingleResult() is only for cases where the query always returns exactly one result. It throws an exception when zero or many results are returned by the database.

  • Query#getResultStream() allows results to be retrieved incrementally, using a database cursor.

Example 541. Executing a query using getResultList()
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class)
.setParameter("name", "J%")
.getResultList();
Example 542. Executing a query using getSingleResult()
Person person = (Person) entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name")
.setParameter("name", "J%")
.getSingleResult();
Example 543. Executing a query using getResultStream()
try(Stream<Person> personStream = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class)
.setParameter("name", "J%")
.getResultStream()) {
	List<Person> persons = personStream
		.skip(5)
		.limit(5)
		.collect(Collectors.toList());
}

The getResultStream() method isn’t usually useful. It’s almost always a bad idea to hold open a database cursor.

16.3.3. Pagination and limits

The very important methods Query#setMaxResults() and Query#setFirstResult() are used to limit the number of results and control pagination.

Example 544. Limits and pagination
Person person = entityManager.createQuery(
		"select p " +
		"from Person p " +
		"where p.name = :name",
		Person.class)
	.setParameter("name", "John Doe")
	.setMaxResults(1)
	.getSingleResult();

List<Person> people = entityManager.createQuery(
		"select p " +
		"from Person p " +
		"where p.name like :name",
		Person.class)
	.setParameter("name", "J%")
	.setFirstResult(page*10)
	.setMaxResults(10)
	.getResultList();

16.3.4. Using query hints to control query execution

When working with the Jakarta Persistence API, advanced control over query execution is possible via named query hints. For example, we may want to specify an execution timeout or control caching.

Example 545. Query execution using a query hint
Person query = entityManager.createQuery(
		"select p " +
		"from Person p " +
		"where p.name like :name",
		Person.class)
	// timeout - in milliseconds
	.setHint("jakarta.persistence.query.timeout", 2000)
	// flush only at commit time
	.setFlushMode(FlushModeType.COMMIT)
	.setParameter("name", "J%")
	.getSingleResult();

Jakarta Persistence defines some standard hints with the prefix jakarta.persistence, but most hints are provider specific. Using provider-specific hints limits your program’s portability to only a small degree.

Hint name Interpretation Equivalent Hibernate API

jakarta.persistence.query.timeout

The query timeout, in milliseconds.

Query#setTimeout()

jakarta.persistence.fetchgraph

An EntityGraph to be interpreted as a fetchgraph, as defined by the Jakarta Persistence specification.

See Fetching.

jakarta.persistence.loadgraph

An EntityGraph to be interpreted as a loadgraph, as defined by the Jakarta Persistence specification.

See Fetching.

org.hibernate.cacheMode

The CacheMode to use.

Query#setCacheMode()

org.hibernate.cacheable

true if the query is cacheable.

Query#setCacheable()

org.hibernate.cacheRegion

For a cacheable query, the name of a cache region to use.

Query#setCacheRegion()

org.hibernate.comment

A comment to apply to the generated SQL.

Query#setComment()

org.hibernate.fetchSize

The JDBC fetch size to use.

Query#setFetchSize()

org.hibernate.flushMode

The Hibernate-specific FlushMode to use.

(Where possible, prefer jakarta.persistence.Query#setFlushMode().)

Query#setFlushMode()

org.hibernate.readOnly

true if entities and collections loaded by this query should be marked as read-only.

Query#setReadOnly()

For named queries, query hints may be specified using the @QueryHint annotation.

16.3.5. Advanced control over query execution

When working directly with a Hibernate Session, the interface org.hibernate.Query is used to control the execution of the query.

Whereas we needed to specify some information using query hints when working with the Jakarta Persistence API, here we have typesafe setters:

Query#setTimeout()

Sets the JDBC-level query timeout.

Query#setFetchSize()

Sets the JDBC-level fetch size.

Query#setCacheable() and setCacheRegion()

Control query caching.

Query#setCacheMode()

Overrides the session-level cache mode.

Query#setFlushMode()

Overrides the session-level flush mode. Flushing is covered in detail in Flushing.

Query#setLockMode()

Overrides the session-level flush mode. Locking is covered in detail in Locking.

Query#setReadOnly()

Overrides the session-level default for read-only state. The concept of read-only state is covered in Persistence Contexts.

Query#setComment()

Adds a comment to the generated SQL.

Query#addQueryHint()

Add a hint to the generated SQL.

addQueryHint() allows specification of a hint intended for the database query planner. A hint is added directly to the generated SQL according to Dialect#getQueryHintString().

On the other hand, setHint() refers to the Jakarta Persistence notion of a query hint, a hint that targets the provider (Hibernate). This is a completely different concept.

For complete details, see the Query Javadocs.

Example 546. Advanced query control
org.hibernate.query.Query<Person> query = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class)
// timeout - in seconds
.setTimeout(2)
// write to L2 caches, but do not read from them
.setCacheMode(CacheMode.REFRESH)
// assuming query cache was enabled for the SessionFactory
.setCacheable(true)
// add a comment to the generated SQL if enabled via the hibernate.use_sql_comments configuration property
.setComment("+ INDEX(p idx_person_name)");

16.3.6. Query result transformers

A program may hook into the process of building the query results by providing a org.hibernate.transform.ResultListTransformer or org.hibernate.transform.TupleTransformer.

See the Javadocs along with the built-in implementations for additional details.

16.3.7. Querying for read-only entities

As explained in entity immutability, fetching entities in read-only mode is more efficient than fetching entities whose state changes might need to be written to the database. Fortunately, even mutable entities may be fetched in read-only mode, with the benefit of reduced memory footprint and of a faster flushing process.

Read-only entities are skipped by the dirty checking mechanism as illustrated by the following example:

Example 547. Read-only entities query example
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"join c.phone p " +
	"where p.number = :phoneNumber ",
	Call.class)
.setParameter("phoneNumber", "123-456-7890")
.setHint("org.hibernate.readOnly", true)
.getResultList();

calls.forEach(c -> c.setDuration(0));
select
    c.id,
    c.duration,
    c.phone_id,
    c.call_timestamp
from
    phone_call c
join
    Phone p
        on p.id=c.phone_id
where
    p.phone_number='123-456-7890'

In this example, no SQL UPDATE was executed.

The method Query#setReadOnly() is an alternative to using a Jakarta Persistence query hint:

Example 548. Read-only entities native query example
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"join c.phone p " +
	"where p.number = :phoneNumber ",
	Call.class)
.setParameter("phoneNumber", "123-456-7890")
.unwrap( org.hibernate.query.Query.class)
.setReadOnly(true)
.getResultList();

16.4. Scrolling and streaming results

The org.hibernate.Query interface offers two specialized operations for reading query results incrementally, while maintaining an open JDBC ResultSet mapped to a server-side cursor.

16.4.1. Scrollable result sets

Query#scroll() returns a org.hibernate.ScrollableResults which wraps an underlying JDBC scrollable ResultSet. Depending on the specified ScrollMode, and on the capabilities of the JDBC driver, the ScrollableResults may allow navigation of the ResultSet in either direction.

Example 549. Scrolling through a ResultSet containing entities
try (ScrollableResults<Person> scrollableResults = session.createQuery(
		"select p " +
		"from Person p " +
		"where p.name like :name",
		Person.class)
		.setParameter("name", "J%")
		.scroll()
) {
	while (scrollableResults.next()) {
		Person person = scrollableResults.get();
		process(person);
	}
}

If a ScrollableResults is left unclosed by the application, Hibernate will automatically close the underlying resources when the transaction ends. However, it’s much better to close the ResultSet as soon as possible.

Since this method holds the JDBC ResultSet open, the program should always close a ScrollableResults either explicitly, by calling close(), or using a try-with-resources block.

If you plan to use Query#scroll with collection fetching, it’s important that your query explicitly order the results so that the JDBC results contain the related rows sequentially.

16.4.2. Streamed result sets

Similarly, getResultStream() is a specialized operation for reading query results incrementally, while maintaining an open JDBC ResultSet mapped to a server-side cursor.

The getResultStream() method is not just a convenient way to obtain a Java Stream. For that, use getResultList().stream().

Example 550. Hibernate getResultStream() with a projection result type
try (Stream<Object[]> persons = session.createQuery(
	"select p.name, p.nickName " +
	"from Person p " +
	"where p.name like :name",
	Object[].class)
.setParameter("name", "J%")
.getResultStream()) {
	persons.map(row -> new PersonNames((String) row[0], (String) row[1]))
		.forEach(this::process);
}
Example 551. Hibernate getResultStream() with an entity result type
try(Stream<Person> persons = session.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like :name",
	Person.class)
.setParameter("name", "J%")
.getResultStream()) {

	Map<Phone, List<Call>> callRegistry = persons
			.flatMap(person -> person.getPhones().stream())
			.flatMap(phone -> phone.getCalls().stream())
			.collect(Collectors.groupingBy(Call::getPhone));

	process(callRegistry);
}

Hibernate will automatically close the underlying resources (the JDBC ResultSet) when the transaction ends. However, it’s much better to close the ResultSet as soon as possible.

The program should always close a Stream either explicitly, by calling close(), or using a try-with-resources block.

16.5. Entity query plan cache

Any entity query, be it JPQL or Criteria API, has to be parsed into an AST (Abstract Syntax Tree) so that Hibernate can generate the proper SQL statement. The entity query compilation takes time, and for this reason, Hibernate offers a query plan cache.

When executing an entity query, Hibernate first checks the plan cache, and only if there’s no plan available, a new one will be computed right away.

The query plan cache can be configured via the following configuration properties:

hibernate.query.plan_cache_max_size

This setting gives the maximum number of entries of the plan cache. The default value is 2048.

hibernate.query.plan_parameter_metadata_max_size

The setting gives the maximum number of ParameterMetadataImpl instances maintained by the query plan cache. The ParameterMetadataImpl object encapsulates metadata about parameters encountered within a query. The default value is 128.

Now, if you have many JPQL or Criteria API queries, it’s a good idea to increase the query plan cache size so that the vast majority of executing entity queries can skip the compilation phase, therefore reducing execution time.

To get a better understanding of the query plan cache effectiveness, Hibernate offers several statistics you can use. For more details, check out the Query plan cache statistics section.

16.6. SelectionQuery

Hibernate’s SelectionQuery contract is similar to Query but only exposes methods which are relevant to selection queries. For example, it does not expose a #executeUpdate method. This allows for earlier validation of the query as a selection.

Example 552. Selection query validation
// can be validated while creating the SelectionQuery
SelectionQuery<?> badQuery = session.createSelectionQuery( "delete Person" );

// cannot be validated until execution
Query query = session.createQuery( "delete Person", Person.class );
query.getResultList();

SelectionQuery may also be used with named-queries

Example 553. NamedQuery selection validation
// can be validated while creating the SelectionQuery
SelectionQuery<?> badQuery = session.getNamedQuery( "delete_Person" );

// cannot be validated until execution
Query query = session.getNamedQuery( "delete_Person" );
query.getResultList();

16.7. MutationQuery

Along the same lines as SelectionQuery, MutationQuery is similar to Query but only exposes methods which are relevant to mutation queries. For example, in terms of execution, it only exposes #executeUpdate method. This allows for earlier validation of the query as a mutation.

Example 554. Mutation query validation
// can be validated while creating the MutationQuery
MutationQuery badQuery = session.createMutationQuery( "select p from Person p" );

// cannot be validated until execution
Query<Person> query = session.createQuery( "select p from Person p", Person.class );
query.executeUpdate();

MutationQuery may also be used with named-queries

Example 555. NamedQuery mutation validation
// can be validated while creating the MutationQuery
MutationQuery badQuery = session.createNamedMutationQuery( "get_person_by_name" );

// cannot be validated until execution
Query query = session.createNamedQuery( "get_person_by_name", Person.class );
query.getResultList();

17. Hibernate Query Language

This chapter describes Hibernate Query Language (HQL) and Jakarta Persistence Query Language (JPQL).

JPQL was inspired by early versions of HQL, and is a subset of modern HQL. Here we focus on describing the complete, more powerful HQL language as it exists today.

If strict Jakarta Persistence compliance is desired, use the setting hibernate.jpa.compliance.query=true. With this configuration, any attempt to use HQL features beyond the JPQL subset will result in an exception. We don’t recommend the use of this setting.

HQL (and JPQL) are loosely based on SQL and are easy to learn for anyone familiar with SQL.

17.1. Identifiers and case sensitivity

An identifier is a name used to refer to an entity, an attribute of a Java class, an identification variable, or a function.

For example, Person, name, p, and upper are all identifiers, but they refer to different kinds of things. In HQL and JPQL, the case sensitivity of an identifier depends on the kind of thing the identifier refers to.

The rules for case sensitivity are:

  • keywords and function names are case-insensitive, but

  • identification variable names, Java class names, and the names of attributes of Java classes, are case-sensitive.

Incidentally, it’s standard practice to use lowercase keywords in HQL and JPQL.

The use of uppercase keywords indicates an endearing but unhealthy attachment to the culture of the 1970’s.

Just to reiterate these rules:

  • select, SeLeCT, sELEct, and SELECT are all the same, and also

  • upper(name) and UPPER(name) are the same, but

  • from BackPack and from Backpack are different, referring to different Java classes, and similarly,

  • person.nickName and person.nickname are different, since the path expression element nickName refers to an attribute of an entity defined in Java, and finally,

  • person.nickName, Person.nickName, and PERSON.nickName are also all different, since the first element of a path expression is an identification variable.

The JPQL specification defines identification variables as case-insensitive.

And so in strict JPA-compliant mode, Hibernate treats person.nickName, Person.nickName, and PERSON.nickName as the same.

A quoted identifier is written in backticks. Quoting lets you use a keyword as an identifier, for example thing.`select` .

17.2. Statement types

HQL features four different kinds of statement:

  • select queries,

  • update statements,

  • delete statements, and

  • insert …​ values and insert …​ select statements.

The effect of an update or delete statement is not reflected in the persistence context, nor in the state of entity objects held in memory at the time the statement is executed.

It is the responsibility of the application to maintain synchronization of state held in memory with the database after execution of an update or delete statement.

17.2.1. Select statements

The full BNF for a select query is quite complicated.

selectStatement
	: queryExpression

queryExpression
	: withClause? orderedQuery (setOperator orderedQuery)*

orderedQuery
	: (query | "(" queryExpression ")") queryOrder?

query
	: selectClause fromClause? whereClause? (groupByClause havingClause?)?
	| fromClause whereClause? (groupByClause havingClause?)? selectClause?

queryOrder
	: orderByClause limitClause? offsetClause? fetchClause?

fromClause
	: FROM entityWithJoins ("," entityWithJoins)*

entityWithJoins
	: fromRoot (join | crossJoin | jpaCollectionJoin)*

fromRoot
	: entityName variable?
	| "LATERAL"? "(" subquery ")" variable?

join
	: joinType "JOIN" "FETCH"? joinTarget joinRestriction?

joinTarget
	: path variable?
	| "LATERAL"? "(" subquery ")" variable?

withClause
	: "WITH" cte ("," cte)*
	;

cte
	: identifier AS ("NOT"? "MATERIALIZED")? "(" queryExpression ")" searchClause? cycleClause?
	;

cteAttributes
	: identifier ("," identifier)*
	;

searchClause
	: "SEARCH" ("BREADTH"|"DEPTH") "FIRST BY" searchSpecifications "SET" identifier
	;

searchSpecifications
	: searchSpecification ("," searchSpecification)*
	;

searchSpecification
	: identifier sortDirection? nullsPrecedence?
	;

cycleClause
	: "CYCLE" cteAttributes "SET" identifier ("TO" literal "DEFAULT" literal)? ("USING" identifier)?
	;

Most of the complexity here arises from the interplay of set operators (union, intersect, and except) with sorting.

We’ll describe the various clauses of a query later in this chapter, but to summarize, a query might have:

  • a with clause, specifying named subqueries to be used in the following query,

  • a select list, specifying a projection (the things to return from the query),

  • a from clause and joins, specifying the entities involved in the query, and how they’re related to each other,

  • a where clause, specifying a restriction,

  • a group by clause, for aggregation,

  • a having clause, specifying a restriction to apply after aggregation,

  • set operators applied to the results of multiple subqueries,

  • an order by clause, for sorting the results, and even

  • a limit/offset clause, for limiting or paginating the results.

Every one of these clauses is optional!

For example, the simplest query in HQL has no select clause at all:

List<Person> persons = session.createQuery(
	"from Person", Person.class)
.getResultList();

We don’t necessarily recommend leaving off the select list.

HQL doesn’t require a select clause, but JPQL does.

Naturally, the previous query may be written with a select clause:

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p",
	Person.class)
.getResultList();

When there’s no explicit select clause, the select list is implied by the result type of the query:

// result type Person, only the Person selected
List<Person> persons = session.createQuery(
	"from Person join phones", Person.class)
	.getResultList();
for (Person person: persons) {
	//...
}

// result type Object[], both Person and Phone selected
List<Object[]> personsWithPhones = session.createQuery(
	"from Person join phones", Object[].class)
	.getResultList();
for (Object[] personWithPhone: personsWithPhones) {
	Person p = (Person) personWithPhone[0];
	Phone ph = (Phone) personWithPhone[1];
	//...
}

For complicated queries, it’s probably best to explicitly specify a select list.

An alternative "simplest" query has only a select list:

LocalDateTime datetime = session.createQuery(
	"select local datetime",
	LocalDateTime.class)
.getSingleResult();

This results in a SQL from dual query (or equivalent).

Looking carefully at the BNF given above, you might notice that the select list may occur either at the beginning of a query, or near the end, right before order by.

Of course, standard SQL, and JPQL, require that the select list comes at the beginning. But it’s more natural to put it last:

List<String> datetimes = session.createQuery(
	"from Person p select p.name",
	String.class)
.getResultList();

This form of the query is more readable, because the alias is declared before it’s used, just as God and nature intended.

17.2.2. Update statements

The BNF for an update statement is much easier to understand:

updateStatement
    : "UPDATE" "VERSIONED"? targetEntity setClause whereClause?

targetEntity
	: entityName variable?

setClause
	: "SET" assignment ("," assignment)*

assignment
    : simplePath "=" expression

The set clause has a list of assignments to attributes of the given entity.

For example:

entityManager.createQuery(
	"update Person set nickName = 'Nacho' " +
	"where name = 'Ignacio'")
.executeUpdate();

An update statement must be executed using Query#executeUpdate(). A single HQL update statement might result in multiple SQL update statements executed against the database.

int updatedEntities = entityManager.createQuery(
	"update Person p " +
	"set p.name = :newName " +
	"where p.name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();

int updatedEntities = session.createMutationQuery(
	"update Person " +
	"set name = :newName " +
	"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();

The integer value returned by executeUpdate() indicates the number of entity instances affected by the operation.

In a JOINED inheritance hierarchy, multiple rows are required to store a single entity instance. In this case, the update count returned by Hibernate might not be exactly the same as the number of rows affected in the database.

An update statement, by default, does not affect the @Version column of the affected entities.

Adding the keyword versioned—writing update versioned—specifies that Hibernate should update the version or update timestamp.

update versioned does not work with custom version types defined by implementing UserVersionType, and is not available in JPQL.

int updatedEntities = session.createMutationQuery(
	"update versioned Person " +
	"set name = :newName " +
	"where name = :oldName")
.setParameter("oldName", oldName)
.setParameter("newName", newName)
.executeUpdate();

Update statements are polymorphic, and affect mapped subclasses of the given entity class.

No update or delete statement may have an implicit (or explicit) join.

17.2.3. Delete statements

The BNF for a delete statement is also quite simple:

deleteStatement
    : "DELETE" "FROM"? targetEntity whereClause?

A delete statement is executed by calling Query#executeUpdate(). A single HQL delete statement might result in multiple SQL delete statements executed against the database.

The integer value returned by executeUpdate() indicates the number of entity instances affected by the operation.

Delete statements are polymorphic, and affect mapped subclasses of the given entity class.

17.2.4. Insert statements

There are two kinds of insert statement:

  • insert …​ values, where the attribute values to insert are given directly as tuples, and

  • insert …​ select, where the inserted attribute values are sourced from a subquery.

The first form inserts a single row in the database, or multiple rows if you provide multiple tuples in the values clause. The second form may insert many new rows, or none at all.

The first sort of insert statement is not as useful. It’s usually better to just use persist().

On the other hand, you might consider using it to set up test data.

The BNF for an insert statement is:

insertStatement
    : "INSERT" "INTO"? targetEntity targetFields (queryExpression | valuesList)

targetEntity
	: entityName variable?

targetFields
	: "(" simplePath ("," simplePath)* ")"

valuesList
	: "VALUES" values ("," values)*

values
	: "(" expression ("," expression)* ")"

For example:

entityManager.createQuery(
	"insert Person (id, name) " +
	"values (100L, 'Jane Doe')")
.executeUpdate();
entityManager.createQuery(
	"insert Person (id, name) " +
	"values (101L, 'J A Doe III'), " +
	"(102L, 'J X Doe'), " +
	"(103L, 'John Doe, Jr')")
.executeUpdate();
int insertedEntities = session.createMutationQuery(
	"insert into Partner (id, name) " +
	"select p.id, p.name " +
	"from Person p ")
.executeUpdate();

An insert statement must be executed by calling Query#executeUpdate().

An insert statement is inherently not polymorphic! Its list of target fields is of fixed length, whereas each subclass of an entity class might declare additional fields. If the entity is involved in a mapped inheritance hierarchy, only attributes declared directly by the named entity and its superclasses may occur in the list of target fields. Attributes declared by subclasses may not occur.

The queryExpression may be any valid select query, with the caveat that the types of the values in the select list must match the types of the target fields.

This is checked during query compilation rather than allowing the type check to delegate to the database. This may cause problems when two Java types map to the same database type. For example, an attribute of type LocalDateTime and an attribute or type Timestamp both map to the SQL type timestamp, but are not considered assignable by the query compiler.

There are two ways to assign a value to the @Id attribute:

  • explicitly specify the id attribute in the list of target fields, and its value in the values assigned to the target fields, or

  • omit it, in which case a generated value is used.

Of course, the second option is only available for entities with database-level id generation (sequences or identity/autoincrement columns). It’s not available for entities whose id generator is implemented in Java, nor for entities whose id is assigned by the application.

The same two options are available for a @Version attribute. When no version is explicitly specified, the version for a new entity instance is used.

insert …​ select statements are not available in JPQL.

17.3. Literals

We now switch gears, and begin describing the language from the bottom up. The very bottom of a programming language is its syntax for literal values.

The most important literal value in this language is null. It’s assignable to any other type.

17.3.1. Boolean literals

The boolean literal values are the (case-insensitive) keywords true and false.

17.3.2. String literals

String literals are enclosed in single quotes.

To escape a single quote within a string literal, use a doubled single quote: ''.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like 'Joe'",
	Person.class)
.getResultList();

// Escaping quotes
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like 'Joe''s'",
	Person.class)
.getResultList();

17.3.3. Numeric literals

Numeric literals come in several different forms.

// simple integer literal
Person person = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.id = 1",
	Person.class)
.getSingleResult();

// simple integer literal, typed as a long
Person person = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.id = 1L",
	Person.class)
.getSingleResult();

// decimal notation
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration > 100.5",
	Call.class)
.getResultList();

// decimal notation, typed as a float
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration > 100.5F",
	Call.class)
.getResultList();

// scientific notation
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration > 1e+2",
	Call.class)
.getResultList();

// scientific notation, typed as a float
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration > 1e+2F",
	Call.class)
.getResultList();

The type of a numeric literal may be specified using a Java-style postfix:

Postfix Type Java type

L or l

long integer

long

D or d

double precision

double

F or f

single precision

float

BI or bi

large integer

BigInteger

BD or bd

exact decimal

BigDecimal

It’s not usually necessary to specify the precision explicitly.

In a literal with an exponent, the E is case-insensitive. Similarly, the Java-style postfix is case-insensitive.

Hexadecimal literals may be written using the same syntax as Java: 0X1A2B or 0x1a2b.

17.3.4. Date and time literals

According to the JPQL specification, date and time literals may be specified using the JDBC escape syntax. Since this syntax is rather unpleasant to look at, HQL provides not one, but two alternatives.

Date/time type Recommended Java type JDBC escape syntax Braced literal syntax Explicitly typed literal syntax

Date

LocalDate

{d 'yyyy-mm-dd'}

{yyyy-mm-dd}

date yyyy-mm-dd

Time

LocalTime

{t 'hh:mm'}

{hh:mm}

time hh:mm

Time with seconds

LocalTime

{t 'hh:mm:ss'}

{hh:mm:ss}

time hh:mm:ss

Datetime

LocalDateTime

{ts 'yyyy-mm-ddThh:mm:ss'}

{yyyy-mm-dd hh:mm:ss}

datetime yyyy-mm-dd hh:mm:ss

Datetime with milliseconds

LocalDateTime

{ts 'yyyy-mm-ddThh:mm:ss.millis'}

{yyyy-mm-dd hh:mm:ss.millis}

datetime yyyy-mm-dd hh:mm:ss.millis

Datetime with an offset

OffsetDateTime

{ts 'yyyy-mm-ddThh:mm:ss+hh:mm'}

{yyyy-mm-dd hh:mm:ss +hh:mm}

datetime yyyy-mm-dd hh:mm:ss +hh:mm

Datetime with a time zone

OffsetDateTime

{ts 'yyyy-mm-ddThh:mm:ss GMT'}

{yyyy-mm-dd hh:mm:ss GMT}

datetime yyyy-mm-dd hh:mm:ss GMT

Literals referring to the current date and time are also provided. Again there is some flexibility.

Date/time type Java type Underscore syntax Spaced syntax

Date

java.time.LocalDate

local_date

local date

Time

java.time.LocalTime

local_time

local time

Datetime

java.time.LocalDateTime

local_datetime

local datetime

Offset datetime

java.time.OffsetDateTime

offset_datetime

offset datetime

Instant

java.time.Instant

instant

instant

Date

java.sql.Date

current_date

current date

Time

java.sql.Time

current_time

current time

Datetime

java.sql.Timestamp

current_timestamp

current timestamp

Of these, only local date, local time, local datetime, current_date, current_time, and current_timestamp are defined by the JPQL specification.

The use of date and time types from the java.sql package is strongly discouraged! Always use java.time types in new code.

17.3.5. Duration literals

There are two sorts of duration in HQL:

  • year/quarter/month/week/day durations, and

  • week/day/hour/minute/second/nanosecond durations.

Literal duration expressions are of form n unit, for example 1 day or 10 year or 100 nanosecond.

The unit may be: day, month, quarter, year, second, minute, hour, or nanosecond.

A HQL duration is considered to map to a Java java.time.Duration, but semantically they’re perhaps more similar to an ANSI SQL INTERVAL type.

17.3.6. Binary string literals

HQL also provides a choice of formats for binary strings:

  • the braced syntax {0xDE, 0xAD, 0xBE, 0xEF}, a list of Java-style hexadecimal byte literals, or

  • the quoted syntax X’DEADBEEF' or x’deadbeef', similar to SQL.

17.3.7. Enum literals

Literal values of a Java enumerated type may be written without needing to specify the enum class name:

// select clause date/time arithmetic operations
List<Phone> phones1 = entityManager.createQuery(
	"from Phone ph " +
	"where ph.type = LAND_LINE",
	Phone.class)
	.getResultList();

Here, the enum class is inferred from the type of the expression on the left of the relational operator.

17.3.8. Java constants

HQL allows any Java static constant to be used in HQL, but it must be referenced by its fully-qualified name:

// select clause date/time arithmetic operations
Double pi = entityManager.createQuery(
	"select java.lang.Math.PI",
	Double.class)
.getSingleResult();

17.3.9. Literal entity names

Entity names may also occur as a literal value. They do not need to be qualified. See Types and typecasts.

17.4. Expressions

Essentially, expressions are references that resolve to basic or tuple values.

17.4.1. String concatenation

HQL defines two ways to concatenate strings:

  • the SQL-style concatenation operator, ||, and

  • the JPQL-standard concat() function.

See below for details of the concat() function.

String name = entityManager.createQuery(
	"select 'Customer ' || p.name " +
	"from Person p " +
	"where p.id = 1",
	String.class)
.getSingleResult();

Many more operations on strings are defined below, in Functions.

17.4.2. Numeric arithmetic

The basic SQL arithmetic operators, +,-,*, and / are joined by the remainder operator %.

// select clause date/time arithmetic operations
Long duration = entityManager.createQuery(
	"select sum(ch.duration) * :multiplier " +
	"from Person pr " +
	"join pr.phones ph " +
	"join ph.callHistory ch " +
	"where ph.id = 1L ",
	Long.class)
.setParameter("multiplier", 1000L)
.getSingleResult();

// select clause date/time arithmetic operations
Integer years = entityManager.createQuery(
	"select year(local date) - year(p.createdOn) " +
	"from Person p " +
	"where p.id = 1L",
	Integer.class)
.getSingleResult();

// where clause arithmetic operations
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where year(local date) - year(p.createdOn) > 1",
	Person.class)
.getResultList();

The following rules apply to the result of arithmetic operations:

  • If either of the operands is Double/double, the result is a Double

  • else, if either of the operands is Float/float, the result is a Float

  • else, if either operand is BigDecimal, the result is BigDecimal

  • else, if either operand is BigInteger, the result is BigInteger (except for division, in which case the result type is not further defined)

  • else, if either operand is Long/long, the result is Long (except for division, in which case the result type is not further defined)

  • else, (the assumption being that both operands are of integral type) the result is Integer (except for division, in which case the result type is not further defined)

Many more numeric operations are defined below, in Functions.

17.4.3. Datetime arithmetic

Arithmetic involving dates, datetimes, and durations is quite subtle. Here we list the basic operations.

Operator Expression type Example Resulting type

-

Difference between two dates

your.birthday - local date

year/quarter/month/week/day duration

-

Difference between two datetimes

local datetime - record.lastUpdated

week/day/hour/minute/second/nanosecond duration

+

Sum of a date and a year/quarter/month/week/day duration

local date + 1 week

date

+

Sum of a datetime and a week/day/hour/minute/second/nanosecond duration

record.lastUpdated + 1 second

datetime

*

Product of an integer and a duration

billing.cycles * 30 day

duration

by unit

Convert a duration to an integer

(1 year) by day

integer

The by unit operator converts a duration to an integer, for example: (local date - your.birthday) by day evaluates to the number of days you still have to wait.

The function extract(unit from …​) extracts a field from a date, time, or datetime type, for example, extract(year from your.birthday) produces the year in which you were born, and throws away important information about your birthday.

Please carefully note the difference between these two operations: by and extract() both evaluate to an integer, but they have very different uses.

Additional datetime operations, including the useful format() function, are defined below, in Functions.

17.4.4. Identification variables and path expressions

Identification variables, and path expressions beginning with an identification variable are legal expression in almost every context.

17.4.5. Case expressions

Just like in standard SQL, there are two forms of case expression:

  • the simple case expression, and

  • the so-called searched case expression.

Case expressions are verbose. It’s often simpler to use the coalesce(), nullif(), or ifnull() functions, as described below in Functions for working with null values.

Simple case expressions

The syntax of the simple form is defined by:

"CASE" expression ("WHEN" expression "THEN" expression)+ ("ELSE" expression)? END

For example:

List<String> nickNames = entityManager.createQuery(
	"select " +
	"	case p.nickName " +
	"	when 'NA' " +
	"	then '<no nick name>' " +
	"	else p.nickName " +
	"	end " +
	"from Person p",
	String.class)
.getResultList();
Searched case expressions

The searched form has the following syntax:

"CASE" ("WHEN" predicate "THEN" expression)+ ("ELSE" expression)? "END"

For example:

List<String> nickNames = entityManager.createQuery(
	"select " +
	"	case " +
	"	when p.nickName is null " +
	"	then " +
	"		case " +
	"		when p.name is null " +
	"		then '<no nick name>' " +
	"		else p.name " +
	"		end" +
	"	else p.nickName " +
	"	end " +
	"from Person p",
	String.class)
.getResultList();

A case expression may contain complex expression, including operator expressions:

List<Long> values = entityManager.createQuery(
	"select " +
	"	case when p.nickName is null " +
	"		 then p.id * 1000 " +
	"		 else p.id " +
	"	end " +
	"from Person p " +
	"order by p.id",
	Long.class)
.getResultList();

assertEquals(3, values.size());
assertEquals(1L, (long) values.get(0));
assertEquals(2000, (long) values.get(1));
assertEquals(3000, (long) values.get(2));

17.5. Functions

Both HQL and JPQL define some standard functions and make them portable between databases.

A program that wishes to remain portable between Jakarta Persistence providers should in principle limit itself to the use of these functions.

On the other hand, this is an extremely short list. Any nontrivial program will probably need to look beyond it.

In some cases, the syntax of these functions looks a bit funny at first, for example, cast(number as String), or extract(year from date), or even trim(leading '.' from string). This syntax is inspired by standard ANSI SQL, and we promise you’ll get used to it.

HQL abstracts away from the actual database-native SQL functions, letting you write queries which are portable between databases.

For some functions, and always depending on the database, a HQL function invocation translates to a quite complicated SQL expression!

In addition, there are several ways to use a database function that’s not known to Hibernate.

17.5.1. Types and typecasts

The following special functions make it possible to discover or narrow expression types:

Special function Purpose Signature JPA standard

type()

The (concrete) entity name

type(e)

treat()

Narrow an entity type

treat(e as Entity)

cast()

Narrow a basic type

cast(x as Type)

str()

Cast to a string

str(x)

Let’s see what these functions do.

type()

The function type(), applied to an identification variable, evaluates to the entity name of the referenced entity. This is mainly useful when dealing with entity inheritance hierarchies.

List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where type(p) = CreditCardPayment",
	Payment.class)
.getResultList();

// using a parameter instead of a literal entity type
List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where type(p) = :type",
	Payment.class)
.setParameter("type", WireTransferPayment.class)
.getResultList();
treat()

The function treat() may be used to narrow the type of an identification variable. This is useful when dealing with entity inheritance hierarchies.

List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where length(treat(p as CreditCardPayment).cardNumber) between 16 and 20",
	Payment.class)
.getResultList();

The type of the expression treat(p as CreditCardPayment) is the narrowed type, CreditCardPayment, instead of the declared type Payment of p. This allows the attribute cardNumber declared by the subtype CreditCardPayment to be referenced.

The treat() function may even occur in a join.

cast()

The function cast() has a similar syntax, but is used to narrow basic types. Its first argument is usually an attribute of an entity, or a more complex expression involving entity attributes.

The target type is an unqualified Java class name: String, Long, Integer, Double, Float, Character, Byte, BigInteger, BigDecimal, LocalDate, LocalTime, LocalDateTime, etc.

List<String> durations = entityManager.createQuery(
	"select cast(c.duration as String) " +
	"from Call c ",
	String.class)
.getResultList();
str()

The function str(x) is a synonym for cast(x as String).

List<String> timestamps = entityManager.createQuery(
	"select str(c.timestamp) " +
	"from Call c ",
	String.class)
.getResultList();
// Special SQL Server function "str" that converts floats
List<String> timestamps = entityManager.createQuery(
	"select str(cast(duration as float) / 60, 4, 2) " +
	"from Call c ",
	String.class)
.getResultList();

17.5.2. Functions for working with null values

The following functions make it easy to deal with null values:

Function Purpose Signature JPA standard

coalesce()

First non-null argument

coalesce(x, y, z)

ifnull()

Second argument if first is null

ifnull(x,y)

nullif()

null if arguments are equal

nullif(x,y)

coalesce()

An abbreviated case expression that returns the first non-null operand.

List<String> nickNames = entityManager.createQuery(
	"select coalesce(p.nickName, '<no nick name>') " +
	"from Person p",
	String.class)
.getResultList();

List<String> nickNames = entityManager.createQuery(
	"select coalesce(p.nickName, p.name, '<no nick name>') " +
	"from Person p",
	String.class)
.getResultList();
ifnull()

HQL allows ifnull() as a synonym for coalesce() in the case of exactly two arguments.

nullif()

Evaluates to null if its operands are equal, or to its first argument otherwise.

List<String> nickNames = entityManager.createQuery(
	"select nullif(p.nickName, p.name) " +
	"from Person p",
	String.class)
.getResultList();

// equivalent CASE expression
List<String> nickNames = entityManager.createQuery(
	"select " +
	"	case" +
	"	when p.nickName = p.name" +
	"	then null" +
	"	else p.nickName" +
	"	end " +
	"from Person p",
	String.class)
.getResultList();

17.5.3. Functions for working with dates and times

There are some very important functions for working with dates and times.

Special function Purpose Signature JPA standard

extract()

Extract a datetime field

extract(field from x)

format()

Format a datetime as a string

format(datetime as pattern)

trunc() or truncate()

Datetime truncation

truncate(datetime, field)

extract()

The special function extract() obtains a single field of a date, time, or datetime.

Field types include: day, month, year, second, minute, hour, day of week, day of month, week of year, date, time, epoch and more. For a full list of field types, see the Javadoc for TemporalUnit.

List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where extract(date from c.timestamp) = local date",
	Call.class)
.getResultList();

List<Integer> years = entityManager.createQuery(
	"select extract(year from c.timestamp) " +
	"from Call c ",
	Integer.class)
.getResultList();

The following functions are abbreviations for extract():

Function Long form using extract() JPA standard

year(x)

extract(year from x)

month(x)

extract(month from x)

day(x)

extract(day from x)

hour(x)

extract(year from x)

minute(x)

extract(year from x)

second(x)

extract(year from x)

These abbreviations aren’t part of the JPQL standard, but on the other hand they’re a lot less verbose.
List<Integer> years = entityManager.createQuery(
	"select year(c.timestamp) " +
	"from Call c ",
	Integer.class)
.getResultList();
format()

This function formats a date, time, or datetime according to a pattern.

The syntax is format(datetime as pattern), and the pattern must be written in a subset of the pattern language defined by Java’s java.time.format.DateTimeFormatter.

For a full list of format() pattern elements, see the Javadoc for Dialect#appendDatetimeFormat.

trunc() or truncate()

This function truncates a date, time, or datetime to the temporal unit specified by field.

The syntax is truncate(datetime, field). Supported temporal units are: year, month, day, hour, minute or second.

Truncating a date, time or datetime value translates to obtaining a value of the same type in which all temporal units smaller than field have been pruned. For hours, minutes and second this means setting them to 00. For months and days, this means setting them to 01.

17.5.4. Functions for working with strings

Naturally, there are a good number of functions for working with strings.

Function Purpose Syntax JPA standard / ANSI SQL Standard

upper()

The string, with lowercase characters converted to uppercase

upper(s)

✓ / ✓

lower()

The string, with uppercase characters converted to lowercase

lower(s)

✓ / ✓

length()

The length of the string

length(s)

✓ / ✗

concat()

Concatenate strings

concat(x, y, z)

✓ / ✗

locate()

Location of string within a string

locate(s, d), locate(s, d, i)

✓ / ✗

position()

Similar to locate()

position(pattern in string)

✗ / ✓

substring()

Substring of a string (JPQL-style)

substring(s, i), substring(s, i, l)

✓ / ✗

substring()

Substring of a string (ANSI SQL-style)

substring(string from start), substring(string from start for length)

✗ / ✓

trim()

Trim characters from string

See below

✓ / ✓

overlay()

For replacing a substring

overlay(string placing replacement from start), overlay(string placing replacement from start for length)

✗ / ✓

pad()

Pads a string with whitespace, or with a specified character

pad(string with length), pad(string with length leading), pad(string with length trailing), or pad(string with length leading character)

✗ / ✗

left()

The leftmost characters of a string

left(string, length)

✗ / ✗

right()

The rightmost characters of a string

right(string, length)

✗ / ✗

replace()

Replace every occurrence of a pattern in a string

replace(string, pattern, replacement)

✗ / ✗

repeat()

Concatenate a string with itself multiple times

replace(string, times)

✗ / ✗

collate()

Select a collation

collate(p.name as collation)

✗ / ✗

Let’s take a closer look at just some of these.

Contrary to Java, positions of characters within strings are indexed from 1 instead of 0!
concat()

Accepts a variable number of arguments, and produces a string by concatenating them.

List<String> callHistory = entityManager.createQuery(
	"select concat(p.number, ' : ' , cast(c.duration as string)) " +
	"from Call c " +
	"join c.phone p",
	String.class)
.getResultList();
locate()

The JPQL function locate() determines the position of a substring within another string.

  • The optional third argument is used to specify a position at which to start the search.

List<Integer> sizes = entityManager.createQuery(
	"select locate('John', p.name) " +
	"from Person p ",
	Integer.class)
.getResultList();
position()

The position() function has a similar purpose, but follows the ANSI SQL syntax.

List<Integer> sizes = entityManager.createQuery(
	"select position('John' in p.name) " +
	"from Person p ",
	Integer.class)
.getResultList();
substring()

Returns a substring of the given string.

  • The second argument specifies the position of the first character of the substring.

  • The optional third argument specifies the maximum length of the substring.

// JPQL-style
List<String> prefixes = entityManager.createQuery(
	"select substring(p.number, 1, 2) " +
	"from Call c " +
	"join c.phone p",
	String.class)
	.getResultList();

// ANSI SQL-style
List<String> prefixes2 = entityManager.createQuery(
	"select substring(p.number from 1 for 2) " +
	"from Call c " +
	"join c.phone p",
	String.class)
.getResultList();
trim()

The trim() function follows the syntax and semantics of ANSI SQL. It may be used to trim leading characters, trailing characters, or both.

// trim whitespace from both ends
List<String> names1 = entityManager.createQuery(
	"select trim(p.name) " +
	"from Person p ",
	String.class)
.getResultList();

// trim leading spaces
List<String> names2 = entityManager.createQuery(
	"select trim(leading ' ' from p.name) " +
	"from Person p ",
	String.class)
.getResultList();

Its BNF is funky:

trimFunction
    : "TRIM" "(" trimSpecification? trimCharacter? "FROM"? expression ")" ;
trimSpecification
    : "LEADING" | "TRAILING" | "BOTH" ;
collate()

Selects a collation to be used for its string-valued argument. Collations are useful for binary comparisons with < or >, and in the order by clause.

For example, collate(p.name as ucs_basic) specifies the SQL standard collation ucs_basic.

Collations aren’t very portable between databases.

17.5.5. Numeric functions

Of course, we also have a number of functions for working with numeric values.

Function Purpose Signature JPA standard

abs()

The magnitude of a number

abs(x)

sign()

The sign of a number

sign(x)

mod()

Remainder of integer division

mod(n,d)

sqrt()

Square root of a number

sqrt(x)

exp()

Exponential function

exp(x)

power()

Exponentiation

power(x,y)

ln()

Natural logarithm

ln(x)

round()

Numeric rounding

round(number), round(number, places)

trunc() or truncate()

Numeric truncation

truncate(number), truncate(number, places)

floor()

Floor function

floor(x)

ceiling()

Ceiling function

ceiling(x)

log10()

Base-10 logarithm

log10(x)

log()

Arbitrary-base logarithm

log(b,x)

pi

π

pi

sin(), cos(), tan(), asin(), acos(), atan()

Basic trigonometric functions

sin(theta), cos(theta)

atan2()

Two-argument arctangent (range (-π,π])

atan2(y, x)

sinh(), cosh(), tanh()

Hyperbolic functions

sinh(x), cosh(x), tanh(x)

degrees()

Convert radians to degrees

degrees(x)

radians()

Convert degrees to radians

radians(x)

least()

Return the smallest of the given arguments

least(x, y, z)

greatest()

Return the largest of the given arguments

greatest(x, y, z)

List<Integer> abs = entityManager.createQuery(
	"select abs(c.duration) " +
	"from Call c ",
	Integer.class)
.getResultList();
List<Integer> mods = entityManager.createQuery(
	"select mod(c.duration, 10) " +
	"from Call c ",
	Integer.class)
.getResultList();
List<Double> sqrts = entityManager.createQuery(
	"select sqrt(c.duration) " +
	"from Call c ",
	Double.class)
.getResultList();

We haven’t included aggregate functions, ordered set aggregate functions, or Window functions: over in this list, because their purpose is more specialized, and because they come with extra special syntax.

17.5.6. Functions for dealing with collections

The following functions apply to any identification variable that refers to a joined collection.

Function Purpose JPA standard

size()

The size of a collection

element()

The element of a list

index()

The index of a list element

key()

The key of a map entry

value()

The value of a map entry

entry()

The whole entry in a map

elements()

See below

indices()

See below

size()

The number of elements of a collection or to-many association.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where size(p.phones) >= 2",
	Person.class)
.getResultList();
element() and index()

A reference to an element or index of joined list.

key(), value(), and entry()

A reference to a key, value, or entry of a joined map.

elements(), and indices()

Later, in Elements and indices, and in Aggregate functions and collections, we will learn about these special functions for quantifying over the elements or indices of a particular collection.

17.5.7. Functions for working with ids and versions

Finally, the following functions evaluate the id, version, or natural id of an entity, or the foreign key of a to-one association:

Function Purpose JPA standard

id()

The value of the entity @Id attribute.

version()

The value of the entity @Version attribute.

naturalid()

The value of the entity @NaturalId attribute.

fk()

The value of the foreign key column mapped by a @ManyToOne (or logical @ManyToOne) association. Mainly useful with @NotFound mappings.

17.5.8. Functions for dealing with arrays

The following functions deal with SQL array types, which are not supported on every database.

Function Purpose

array()

Creates an array based on the passed arguments

array_list()

Like array, but returns the result as List<?>

array_agg()

Aggregates row values into an array

array_position()

Determines the position of an element in an array

array_positions()

Determines all positions of an element in an array

array_positions_list()

Like array_positions, but returns the result as List<Integer>

array_length()

Determines the length of an array

array_concat()

Concatenates array with each other in order

array_prepend()

Prepends element to array

array_append()

Appends element to array

array_contains()

Whether an array contains element(s)

array_contains_nullable()

Whether an array contains element(s), supporting null elements

array_overlaps()

Whether an array holds at least one element of another array

array_overlaps_nullable()

Whether an array holds at least one element of another array, supporting null elements

array_get()

Accesses the element of an array by index

array_set()

Creates array copy with given element at given index

array_remove()

Creates array copy with given element removed

array_remove_index()

Creates array copy with the element at the given index removed

array_slice()

Creates a sub-array of the based on lower and upper index

array_replace()

Creates array copy replacing a given element with another

array_trim()

Creates array copy trimming the last N elements

array_fill()

Creates array filled with the same element N times

array_fill_list()

Like array_fill, but returns the result as List<?>

array_to_string()

String representation of non-null array elements

array() and array_list()

Creates an array based on the passed arguments, and infers the array type from the context if possible. To retrieve the result as List<?>, use the array_list() function.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where e.theArray = array('abc')", EntityWithArrays.class )
		.getResultList();
array_agg()

An ordered set aggregate function that aggregates values to an array.

List<String[]> results = em.createQuery( "select array_agg(e.data) within group (order by e.id) from BasicEntity e", String[].class )
		.getResultList();
array_position()

Returns the 1-based position of an element in the array. Returns 0 if the element is not found and null if the array is null.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_position(e.theArray, 'abc') = 1", EntityWithArrays.class )
		.getResultList();
array_positions() and array_positions_list()

Returns an int[] of 1-based positions of matching elements in the array. Returns an empty array if the element is not found and null if the array is null. To retrieve the result as List<Integer>, use the array_positions_list() function.

List<int[]> results = em.createQuery( "select array_positions(e.theArray, 'abc') from EntityWithArrays e order by e.id", int[].class )
		.getResultList();
array_length()

Returns size of the passed array. Returns null if the array is null.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_length(e.theArray) = 0", EntityWithArrays.class )
		.getResultList();
array_concat() or ||

Concatenates arrays with each other in order. Returns null if one of the arguments is null.

List<Tuple> results = em.createQuery( "select e.id, array_concat(e.theArray, array('xyz')) from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();

Arrays can also be concatenated with the || (double-pipe) operator.

List<Tuple> results = em.createQuery( "select e.id, e.theArray || array('xyz') from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();

In addition, the || (double-pipe) operator also support concatenating single elements to arrays.

em.createQuery( "select e.id, e.theArray || 'last' from EntityWithArrays e order by e.id" ).getResultList();
array_prepend()

Prepends element to array. Returns null if the array argument is null.

List<Tuple> results = em.createQuery( "select e.id, array_prepend('xyz', e.theArray) from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_append()

Appends element to array. Returns null if the array argument is null.

List<Tuple> results = em.createQuery( "select e.id, array_append(e.theArray, 'xyz') from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_contains() and array_contains_nullable()

Checks if the first array argument contains the element(s) of the second argument. Returns null if the first argument is null. The result of the array_contains function is undefined when the second argument, the element to search, is null.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_contains(e.theArray, 'abc')", EntityWithArrays.class )
		.getResultList();

The second argument may be an array of the same type as the first argument. The result of array_contains is undefined when the second argument is an array that contains a null element.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_contains(e.theArray, array('abc', 'def'))", EntityWithArrays.class )
		.getResultList();

To search for null elements, the array_contains_nullable function must be used with an array argument.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_contains_nullable(e.theArray, array('abc',null))", EntityWithArrays.class )
		.getResultList();
array_overlaps() and array_overlaps_nullable()

Checks if the first array argument any of the elements of the second array argument. Returns null if either of the arguments is null. The result of array_overlaps is undefined when the second array argument contains a null array element. Only array_overlaps_nullable is guaranteed to produce correct results for null array elements.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_overlaps(e.theArray, array('abc', 'def'))", EntityWithArrays.class )
		.getResultList();
List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_overlaps_nullable(e.theArray, array('xyz',null))", EntityWithArrays.class )
		.getResultList();
array_get()

Returns the element of an array at the given 1-based index. Returns null if either of the arguments is null, and also if the index is bigger than the array length.

List<EntityWithArrays> results = em.createQuery( "from EntityWithArrays e where array_get(e.theArray, 1) = 'abc'", EntityWithArrays.class )
		.getResultList();
array_set()

Returns an array copy with the given element placed at the given 1-based index, filling up prior slots with null if necessary.

List<Tuple> results = em.createQuery( "select e.id, array_set(e.theArray, 1, 'xyz') from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_remove()

Returns an array copy with the given element removed from the array. Allows removal of null elements.

List<Tuple> results = em.createQuery( "select e.id, array_remove(e.theArray, 'abc') from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_remove_index()

Returns an array copy with the element at the given index removed from the array.

List<Tuple> results = em.createQuery( "select e.id, array_remove_index(e.theArray, 1) from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_slice()

Returns the sub-array as specified by the given start and end index. Returns null if any of the arguments is null and also if the index is out of bounds.

List<Tuple> results = em.createQuery( "select e.id, array_remove_index(e.theArray, 1) from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_replace()

Returns an array copy which has elements matching the second argument replaced by the third argument.

List<Tuple> results = em.createQuery( "select e.id, array_replace(e.theArray, 'abc', 'xyz') from EntityWithArrays e order by e.id", Tuple.class )
		.getResultList();
array_trim()

Returns an array copy without the last N elements, specified by the second argument. It is an error if any array has a length smaller than the second argument.

List<Tuple> results = em.createQuery( "select e.id, array_trim(e.theArray, 1) from EntityWithArrays e where e.id = 2", Tuple.class )
		.getResultList();
array_fill() and array_fill_list()

Creates an array filled with the same element N times as specified by the arguments. It is an error to supply an array length smaller than 0. To retrieve the result as List<?>, use the array_fill_list() function.

List<String[]> results = em.createQuery( "select array_fill('aaa', 2)", String[].class )
		.getResultList();
array_to_string()

Concatenates the non-null array elements with a separator, as specified by the arguments. Returns null if the first argument is null.

List<String> results = em.createQuery( "select array_to_string(e.theArray, ',') from EntityWithArrays e", String.class )
		.getResultList();

17.5.9. Native and user-defined functions

The functions we’ve described above are the functions abstracted by HQL and made portable across databases. But, of course, HQL can’t abstract every function in your database.

There are several ways to call native or user-defined SQL functions.

  • A native or user-defined function may be called using JPQL’s function syntax, for example, function('sinh', phi). (This is the easiest way, but not the best way.)

  • A user-written FunctionContributor may register user-defined functions.

  • A custom Dialect may register additional native functions by overriding initializeFunctionRegistry().

Registering a function isn’t hard, but is beyond the scope of this chapter.

(It’s even possible to use the APIs Hibernate provides to make your own portable functions!)

Fortunately, every built-in Dialect already registers many native functions for the database it supports.

Try setting the log category org.hibernate.HQL_FUNCTIONS to debug. Then at startup Hibernate will log a list of type signatures of all registered functions.

// careful: these functions are not supported on all databases!

List<Tuple> variances = entityManager.createQuery(
	"select var_samp(c.duration) as sampvar, var_pop(c.duration) as popvar " +
	"from Call c ",
	Tuple.class)
.getResultList();

List<Number> bits = entityManager.createQuery(
	"select bit_length(c.phone.number) " +
	"from Call c ",
	Number.class)
.getResultList();

17.5.10. Embedding native SQL in HQL

The special function sql() allows the use of native SQL fragments inside an HQL query.

The signature of this function is sql(pattern[, argN]*), where pattern must be a string literal but the remaining arguments may be of any type. The pattern literal is unquoted and embedded in the generated SQL. Occurrences of ? in the pattern are replaced with the remaining arguments of the function.

-- Cast to some native type
select c from Computer c where c.ipAddress = sql('?::inet', '127.0.0.1')
-- Use some native operator
select h from Human h order by sql('(? <-> ?)', h.workLocation, h.homeLocation)

17.6. Predicates

A predicate is an operator which, when applied to some argument, evaluates to true or false. In the world of SQL-style ternary logic, we must expand this definition to encompass the possibility that the predicate evaluates to null. Typically, a predicate evaluates to null when one of its arguments is null.

Predicates occur in the where clause, the having clause and in searched case expressions.

17.6.1. Relational operators

The binary comparison operators are borrowed from SQL: =, >, >=, <, <=, <>.

If you prefer, HQL treats != as a synonym for <>.

The operands should be of the same type.

// numeric comparison
List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration < 30 ",
	Call.class)
.getResultList();

// string comparison
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like 'John%' ",
	Person.class)
.getResultList();

// datetime comparison
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.createdOn > date 1950-01-01 ",
	Person.class)
.getResultList();

// enum comparison
List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where p.type = 'MOBILE' ",
	Phone.class)
.getResultList();

// boolean comparison
List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where p.completed = true ",
	Payment.class)
.getResultList();

// boolean comparison
List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where type(p) = WireTransferPayment ",
	Payment.class)
.getResultList();

// entity value comparison
List<Object[]> phonePayments = entityManager.createQuery(
	"select p " +
	"from Payment p, Phone ph " +
	"where p.person = ph.person ",
	Object[].class)
.getResultList();

17.6.2. between

The ternary between operator, and its negation, not between, determine if a value falls within a range.

Of course, all three operands must be of compatible type.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"join p.phones ph " +
	"where p.id = 1L and index(ph) between 0 and 3",
	Person.class)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.createdOn between date 1999-01-01 and date 2001-01-02",
	Person.class)
.getResultList();

List<Call> calls = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"where c.duration between 5 and 20",
	Call.class)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name between 'H' and 'M'",
	Person.class)
.getResultList();

17.6.3. Operators for dealing with null

The following operators make it easier to deal with null values.

Operator Negation Type Semantics

is null

is not null

Unary postfix

true if the value to the left is null

is distinct from

is not distinct from

Binary

true if the value on the left is equal to the value on the right, or if both are null

// select all persons with a nickname
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.nickName is not null",
	Person.class)
.getResultList();

// select all persons without a nickname
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.nickName is null",
	Person.class)
.getResultList();

17.6.4. Operators for dealing with boolean values

These operators perform comparisons on values of type boolean. These predicates never evaluate to null.

The values true and false of the boolean basic type are different to the logical true or false produced by a predicate.

For logical operations on predicates, see [logical-operators] below.

Operator Negation Type Semantics

is true

is not true

Unary postfix

true if the value to the left is true, or false otherwise

is false

is not false

Binary

true if the value to the left is false, or false otherwise

17.6.5. String pattern matching

The like operator performs pattern matching on strings. Its friend ilike performs case-insensitive matching.

Their syntax is defined by:

expression "NOT"? ("LIKE" | "ILIKE") expression ("ESCAPE" character)?

The expression on the right is a pattern, where:

  • _ matches any single character,

  • % matches any number of characters, and

  • if an escape character is specified, it may be used to escape either of these wildcards.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like 'Jo%'",
	Person.class)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name not like 'Jo%'",
	Person.class)
.getResultList();

The optional escape character allows a pattern to include a literal _ or % character.

For example, to match all stored procedures prefixed with Dr_, the like criteria could be 'Dr|_%' escape '|':

// find any person with a name starting with "Dr_"
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.name like 'Dr|_%' escape '|'",
	Person.class)
.getResultList();

As you can guess, not like and not ilike are the enemies of like and ilike, and evaluate to the exact opposite boolean values.

17.6.6. Elements and indices

There’s two special HQL functions that we mentioned earlier, without giving much of an explanation, since they’re only useful in conjunction with the predicate operators we’re about to meet.

These functions are only allowed in the where clause, and result in a subquery in the generated SQL. Indeed, you can think of them as just a shortcut way to write a subquery.

HQL Function Applies to Purpose

elements()

Any collection

Refers to the elements of a collection as a whole.

indices()

Indexed collections (lists and maps)

Similar to elements() but refers to the collections indices (keys/positions) as a whole.

In the next three sections, we’ll see how these two functions are useful.

17.6.7. in

The in predicates evaluates to true if the value to its left is in …​ well, whatever it finds to its right.

Its syntax is unexpectedly complicated:

expression "NOT"? "IN" inList

inList
	: ("ELEMENTS"|"INDICES") "(" simplePath ")"
	| "(" (expression ("," expression)*)? ")"
	| "(" subquery ")"
	| parameter

This less-than-lovely fragment of the HQL ANTLR grammar tells is that the thing to the right might be:

  • a list of values enclosed in parentheses,

  • a query parameter,

  • a subquery, or

  • one of the functions elements() or indices() defined above.

The type of the expression on the left, and the types of all the values on the right must be compatible.

JPQL limits the legal types to string, numeric, date/time, and enum types, and in JPQL the left expression must be either:

  • a "state field", which means a simple attribute, excluding associations and embedded attributes, or

  • an entity type expression (see Types and typecasts).

HQL is far more permissive. HQL itself does not restrict the type any way, though the database itself might. Even embedded attributes are allowed, although that feature depends on the level of support for tuple or "row value constructors" in the underlying database.

List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p " +
	"where type(p) in (CreditCardPayment, WireTransferPayment)",
	Payment.class)
.getResultList();

List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where type in ('MOBILE', 'LAND_LINE')",
	Phone.class)
.getResultList();

List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where type in :types",
	Phone.class)
.setParameter("types", Arrays.asList(PhoneType.MOBILE, PhoneType.LAND_LINE))
.getResultList();

List<Phone> phones = entityManager.createQuery(
	"select distinct p " +
	"from Phone p " +
	"where p.person.id in (" +
	"	select py.person.id " +
	"	from Payment py" +
	"	where py.completed = true and py.amount > 50 " +
	")",
	Phone.class)
.getResultList();

// Not JPQL compliant!
List<Phone> phones = entityManager.createQuery(
	"select distinct p " +
	"from Phone p " +
	"where p.person in (" +
	"	select py.person " +
	"	from Payment py" +
	"	where py.completed = true and py.amount > 50 " +
	")",
	Phone.class)
.getResultList();

// Not JPQL compliant!
List<Payment> payments = entityManager.createQuery(
	"select distinct p " +
	"from Payment p " +
	"where (p.amount, p.completed) in (" +
	"	(50, true)," +
	"	(100, true)," +
	"	(5, false)" +
	")", Payment.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where 1 in indices(p.phones)",
	Person.class)
.getResultList();

17.6.8. Relational operators and subqueries

The binary comparisons we met above in Relational operators may involve a qualifier:

  • a qualified subquery, or

  • a qualifier applied to one of the functions elements() or indices() defined above.

The qualifiers are unary prefix operators: all, every, any, and some.

Subquery operator Synonym Semantics

every

all

Evaluates to true of the comparison is true for every value in the result set of the subquery.

any

some

Evaluates to true of the comparison is true for at least one value in the result set of the subquery.

// select all persons with all calls shorter than 50 seconds
List<Person> persons = entityManager.createQuery(
	"select distinct p.person " +
	"from Phone p " +
	"join p.calls c " +
	"where 50 > all (" +
	"	select duration" +
	"	from Call" +
	"	where phone = p " +
	") ", Person.class)
.getResultList();
List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where local date > all elements(p.repairTimestamps)",
	Phone.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where :phone = some elements(p.phones)",
	Person.class)
.setParameter("phone", phone)
.getResultList();

// the above query can be re-written with member of
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where :phone member of p.phones",
	Person.class)
.setParameter("phone", phone)
.getResultList();

17.6.9. Exists operator

The unary prefix exists operator evaluates to true if the thing to its right is nonempty.

The thing to its right might be:

  • a subquery, or

  • one of the functions elements() or indices() defined above.

As you can surely guess, not exists evaluates to true if the thing to the right is empty.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where exists elements(p.phones)",
	Person.class)
.getResultList();

17.6.10. Collection operators

The following operators apply to collection-valued attributes and to-many associations.

Operator Negation Type Semantics

is empty

is not empty

Unary postfix

true if the collection or association on the left has no elements

member of

not member of

Binary

true if the value on the left is a member of the collection or association on the right

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.phones is empty",
	Person.class)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.phones is not empty",
	Person.class)
.getResultList();
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where 'Home address' member of p.addresses",
	Person.class)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where 'Home address' not member of p.addresses",
	Person.class)
.getResultList();

17.6.11. Logical operators

The logical operators are binary infix and and or, and unary prefix not.

Just like SQL, logical expressions are based on ternary logic. A logical operator evaluates to null if it has a null operand.

17.7. Declaring root entities: from and cross join

The from clause is responsible for declaring the entities available in the rest of the query, and assigning them aliases, or, in the language of the JPQL specification, identification variables.

17.7.1. Identification variables

An identification variable is just a name we can use to refer to an entity and its attributes from expressions in the query. It may be any legal Java identifier. According to the JPQL specification, identification variables must be treated as case-insensitive language elements.

The identification variable is actually optional, but for queries involving more than one entity it’s almost always a good idea to declare one.

Identification variables may be declared with the as keyword, but this is optional.

17.7.2. Root entity references

A root entity reference, or what the JPQL specification calls a range variable declaration, is a direct reference to a mapped @Entity type by its entity name.

Remember, the entity name is the value of the name member of the @Entity annotation, or the unqualified Java class name by default.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p",
	Person.class)
.getResultList();

In this example, Person is the entity name, and p is the identification variable.

Alternatively, a fully-qualified Java class name may be specified. Then Hibernate will query every entity which inherits the named type.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from org.hibernate.testing.orm.domain.userguide.Person p",
	Person.class)
.getResultList();

Of course, there may be multiple root entities.

List<Object[]> persons = entityManager.createQuery(
	"select distinct pr, ph " +
	"from Person pr, Phone ph " +
	"where ph.person = pr and ph is not null",
	Object[].class)
.getResultList();
List<Person> persons = entityManager.createQuery(
	"select distinct pr1 " +
	"from Person pr1, Person pr2 " +
	"where pr1.id <> pr2.id " +
	"  and pr1.address = pr2.address " +
	"  and pr1.createdOn < pr2.createdOn",
	Person.class)
.getResultList();

The previous queries may even be written using the syntax cross join in place of the comma:

List<Object[]> persons = entityManager.createQuery(
	"select distinct pr, ph " +
	"from Person pr cross join Phone ph " +
	"where ph.person = pr and ph is not null",
	Object[].class)
.getResultList();

17.7.3. Polymorphism

HQL and JPQL queries are inherently polymorphic. Consider:

List<Payment> payments = entityManager.createQuery(
	"select p " +
	"from Payment p ",
	Payment.class)
.getResultList();

This query names the Payment entity explicitly. But the CreditCardPayment and WireTransferPayment entities inherit Payment, and so p ranges over all three types. Instances of all these entities are returned by the query.

The query from java.lang.Object is completely legal. (But not very useful!)

It returns every object of every mapped entity type.

This behavior may be slightly adjusted using the @Polymorphism annotation.

17.7.4. Derived roots

A derived root is an uncorrelated subquery which occurs in the from clause. It must declare an identification variable.

List<Tuple> calls = entityManager.createQuery(
	"select d.owner, d.payed " +
	"from (" +
	"  select p.person as owner, c.payment is not null as payed " +
	"  from Call c " +
	"  join c.phone p " +
	"  where p.number = :phoneNumber) d",
	Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();

This feature can be used to break a more complicated query into smaller pieces.

We emphasize that a derived root must be an uncorrelated subquery. It may not refer to other roots declared in the same from clause.

A subquery may also occur in a join, in which case it may be a correlated subquery.

17.7.5. Common table expressions in from clause

A Common table expression (CTE) is like a derived root with a name. The big difference is, that the name can be referred to multiple times. It must declare an identification variable.

The CTE name can be used for a from clause root or a join, similar to entity names.

Refer to the with clause chapter for details about CTEs.

17.8. Declaring joined entities

Joins allow us to navigate from one entity to another, via its associations, or via explicit join conditions. There are:

  • explicit joins, declared within the from clause using the keyword join, and

  • implicit joins, which don’t need to be declared in the from clause.

An explicit join may be either:

  • an inner join, written as join or inner join,

  • a left outer join, written as left join or left outer join,

  • a right outer join, written as right join or right outer join, or

  • a full outer join, written as full join or full outer join.

17.8.1. Explicit root joins

An explicit root join works just like an ANSI-style join in SQL.

List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"join Phone ph on ph.person = pr " +
	"where ph.type = :phoneType",
	Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();

This looks nice and familiar, but it’s not the most common sort of join in HQL or JPQL.

17.8.2. Explicit association joins

Every explicit association join specifies an entity attribute to be joined. The specified attribute:

  • is usually a @OneToMany, @ManyToMany, @OneToOne, or @ManyToOne association, but

  • it could be an @ElementCollection, and

  • it might even be an attribute of embeddable type.

In the case of an association or collection, the generated SQL will have a join of the same type. (For a many-to-many association it will have two joins.) In the case of an embedded attribute, the join is purely logical and does not result in a join in the generated SQL.

An explicit join may assign an identification variable to the joined entity.

List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"join pr.phones ph " +
	"where ph.type = :phoneType",
	Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();

// same query, but specifying join type as 'inner' explicitly
List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"inner join pr.phones ph " +
	"where ph.type = :phoneType",
	Person.class)
.setParameter("phoneType", PhoneType.MOBILE)
.getResultList();
List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"left join pr.phones ph " +
	"where ph is null " +
	"   or ph.type = :phoneType",
	Person.class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();

// same query, but specifying join type as 'outer' explicitly
List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"left outer join pr.phones ph " +
	"where ph is null " +
	"   or ph.type = :phoneType",
	Person.class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();

For further information about collection-valued association references, see Joining collections and many-valued associations.

17.8.3. Explicit association joins with join conditions

The with or on clause allows explicit qualification of the join conditions.

The specified join conditions are added to the join conditions specified by the foreign key association. That’s why, historically, HQL uses the keword with here: "with" emphasizes that the new condition doesn’t replace the original join conditions.

The with keyword is specific to Hibernate. JPQL uses on.

Join conditions occurring in the with or on clause are added to the on clause in the generated SQL.

List<Object[]> personsAndPhones = session.createQuery(
	"select pr.name, ph.number " +
	"from Person pr " +
	"left join pr.phones ph with ph.type = :phoneType ",
	Object[].class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();

The following query is arguably less clear, but semantically equivalent:

List<Object[]> personsAndPhones = entityManager.createQuery(
	"select pr.name, ph.number " +
	"from Person pr " +
	"left join pr.phones ph on ph.type = :phoneType ",
	Object[].class)
.setParameter("phoneType", PhoneType.LAND_LINE)
.getResultList();

17.8.4. join fetch for association fetching

A fetch join overrides the laziness of a given association, specifying that the association should be fetched with a SQL join. The join may be an inner or outer join.

  • A join fetch, or, more explicitly, inner join fetch, only returns base entities with an associated entity.

  • A left join fetch, or—for lovers of verbosity—left outer join fetch, returns all the base entities, including those which have no associated joined entity.

This is one of the most important features of Hibernate. To achieve acceptable performance with HQL, you’ll need to use join fetch quite often. Without it, you’ll quickly run into the dreaded "n+1 selects" problem.

For example, if Person has a one-to-many association named phones, the use of join fetch in the following query specifies that the collection elements should be fetched in the same SQL query:

List<Person> persons = entityManager.createQuery(
	"select distinct pr " +
	"from Person pr " +
	"left join fetch pr.phones ",
	Person.class)
.getResultList();

In this example, we used a left outer join because we also wanted to obtain customers with no orders.

A query may have more than one fetch join, but be aware that:

  • it’s perfectly safe to fetch several to-one associations in series or parallel in a single query, and

  • a single series of nested fetch joins is also fine, but

  • fetching multiple collections or to-many associations in parallel results in a Cartesian product at the database level, and might exhibit very poor performance.

HQL doesn’t disallow it, but it’s usually a bad idea to apply a restriction to a join fetched entity, since the elements of the fetched collection would be incomplete. Indeed, it’s best to avoid even assigning an identification variable to a fetched joined entity except for the purpose of specifying a nested fetch join.

Fetch joins should usually be avoided in limited or paged queries. This includes:

Nor should they be used with the scroll() and stream() methods described in Scrolling and streaming results.

Fetch joins are disallowed in subqueries, where they would make no sense.

17.8.5. Joins with typecasts

An explicit join may narrow the type of the joined entity using treat().

// a to-many association
List<Object[]> payments = entityManager.createQuery(
	"select a, ccp " +
	"from Account a " +
	"join treat(a.payments as CreditCardPayment) ccp " +
	"where length(ccp.cardNumber) between 16 and 20",
	Object[].class)
.getResultList();

// a to-one association
List<Object[]> payments = entityManager.createQuery(
	"select c, ccp " +
	"from Call c " +
	"join treat(c.payment as CreditCardPayment) ccp " +
	"where length(ccp.cardNumber) between 16 and 20",
	Object[].class)
.getResultList();

Here, the identification variable ccp declared to the right of treat() has the narrowed type CreditCardPayment, instead of the declared type Payment. This allows the attribute cardNumber declared by the subtype CreditCardPayment to be referenced in the rest of the query.

See Types and typecasts for more information about treat().

17.8.6. Subqueries in joins

A join clause may contain a subquery, either:

  • an uncorrelated subquery, which is almost the same as a derived root, except that it may have an on restriction, or

  • a lateral join, which is a correlated subquery, and may refer to other roots declared earlier in the same from clause.

The lateral keyword just distinguishes the two cases.

List<Tuple> calls1 = entityManager.createQuery(
		"from Phone p " +
		"left join (" +
		"  select c.duration as duration, c.phone.id as cid" +
		"  from Call c" +
		"  order by c.duration desc" +
		"  limit 1" +
		"  ) as longest on cid = p.id " +
		"where p.number = :phoneNumber " +
		"select longest.duration",
		Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();

//same, but using 'join lateral' instead of 'on'
List<Tuple> calls2 = entityManager.createQuery(
	"from Phone p " +
	"left join lateral (" +
	"  select c.duration as duration" +
	"  from p.calls c" +
	"  order by c.duration desc" +
	"  limit 1" +
	"  ) as longest " +
	"where p.number = :phoneNumber " +
	"select longest.duration",
	Tuple.class)
.setParameter("phoneNumber", "123-456-7890")
.getResultList();

A lateral join may be an inner or left outer join, but not a right join, nor a full join.

Traditional SQL doesn’t allow correlated subqueries in the from clause. A lateral join is essentially just that, but with a different syntax to what you might expect.

On some databases, join lateral is written cross apply. And on Postgres it’s plain lateral, without join.

It’s almost as if they’re deliberately trying to confuse us.

Lateral joins are particularly useful for computing top-N elements of multiple groups.

Most databases support some flavor of join lateral, and Hibernate emulates the feature for databases which don’t. But emulation is neither very efficient, nor does it support all possible query shapes, so it’s important to test on your target database.

17.8.7. Implicit association joins (path expressions)

It’s not necessary to explicitly join every entity that occurs in a query. Instead, entity associations may be navigated, just like in Java:

  • if an attribute is of embedded type, or is a to-one association, it may be further navigated, but

  • if an attribute is of basic type, is collection-valued, or is a to-many association, it is considered terminal, and may not be further navigated.

It’s clear that:

  • A path expression like p.name with only two elements just refers to state held directly by an entity with an alias p defined in from or join.

  • But a longer path expression, for example, ph.person.name, might refer to state held by an associated entity. (Alternatively, it might refer to state held by an embedded class.)

In the second case, Hibernate with automatically add a join to the generated SQL if necessary.

List<Phone> phones = entityManager.createQuery(
	"select ph " +
	"from Phone ph " +
	"where ph.person.address = :address ",
	Phone.class)
.setParameter("address", address)
.getResultList();

// same as
List<Phone> phones = entityManager.createQuery(
	"select ph " +
	"from Phone ph " +
	"join ph.person pr " +
	"where pr.address = :address ",
	Phone.class)
.setParameter("address", address)
.getResultList();

As in this example, implicit joins usually appear outside the from clause of the HQL query. However, they always affect the from clause of the SQL query.

Note that:

  • Implicit joins are always treated as inner joins.

  • Multiple occurrences of the same implicit join always refer to the same SQL join.

List<Phone> phones = entityManager.createQuery(
	"select ph " +
	"from Phone ph " +
	"where ph.person.address = :address " +
	"  and ph.person.createdOn > :timestamp",
	Phone.class)
.setParameter("address", address)
.setParameter("timestamp", timestamp)
.getResultList();

//same as
List<Phone> phones = entityManager.createQuery(
	"select ph " +
	"from Phone ph " +
	"inner join ph.person pr " +
	"where pr.address = :address " +
	"  and pr.createdOn > :timestamp",
	Phone.class)
.setParameter("address", address)
.setParameter("timestamp", timestamp)
.getResultList();

17.8.8. Joining collections and many-valued associations

When a join involves a collection or many-valued association, the declared identification variable refers to the elements of the collection, that is:

  • to the elements of a Set,

  • to the elements of a List, not to their indices in the list, or

  • to the values of a Map, not to their keys.

List<Phone> phones = entityManager.createQuery(
	"select ph " +
	"from Person pr " +
	"join pr.phones ph " +
	"join ph.calls c " +
	"where pr.address = :address " +
	"  and c.duration > :duration",
	Phone.class)
.setParameter("address", address)
.setParameter("duration", duration)
.getResultList();

In this example, the identification variable ph is of type Phone, the element type of the list Person#phones. But if we need to refer to the index of a Phone in the list, we need some extra syntax.

You might recall that we mentioned element() and index() and key(), value(), and entry() a bit earlier. These functions may be applied to the identification variable declared in a collection join or many-valued association join.

Function Applies to Interpretation Notes

value() or element()

Any collection

The collection element or map entry value

Often optional.

index()

Any List with an index column

The index of the element in the list

For backward compatibility, it’s also an alternative to key(), when applied to a map.

key()

Any Map

The key of the entry in the list

If the key is of entity type, it may be further navigated.

entry()

Any Map

The map entry, that is, the Map.Entry of key and value.

Only legal as a terminal path, and only allowed in the select clause.

In particular, index() and key() obtain a reference to a list index or map key.

@OneToMany(mappedBy = "phone")
@MapKey(name = "timestamp")
private Map<LocalDateTime, Call> callHistory = new HashMap<>();


// select all the calls (the map value) for a given Phone
// note that here we don't need to use value() or element()
// since it is implicit
List<Call> calls = entityManager.createQuery(
	"select ch " +
	"from Phone ph " +
	"join ph.callHistory ch " +
	"where ph.id = :id ",
	Call.class)
.setParameter("id", id)
.getResultList();

// same as above, but with value() explicit
List<Call> calls = entityManager.createQuery(
	"select value(ch) " +
	"from Phone ph " +
	"join ph.callHistory ch " +
	"where ph.id = :id ",
	Call.class)
.setParameter("id", id)
.getResultList();

// select all the Call timestamps (the map key) for a given Phone
// note that here we *do* need to explicitly specify key()
List<LocalDateTime> timestamps = entityManager.createQuery(
	"select key(ch) " +
	"from Phone ph " +
	"join ph.callHistory ch " +
	"where ph.id = :id ",
	LocalDateTime.class)
.setParameter("id", id)
.getResultList();

// select all the Call and their timestamps (the 'Map.Entry') for a given Phone
List<Map.Entry<Date, Call>> callHistory = entityManager.createQuery(
	"select entry(ch) " +
	"from Phone ph " +
	"join ph.callHistory ch " +
	"where ph.id = :id ")
.setParameter("id", id)
.getResultList();

// Sum all call durations for a given Phone of a specific Person
Long duration = entityManager.createQuery(
	"select sum(ch.duration) " +
	"from Person pr " +
	"join pr.phones ph " +
	"join ph.callHistory ch " +
	"where ph.id = :id " +
	"  and index(ph) = :phoneIndex",
	Long.class)
.setParameter("id", id)
.setParameter("phoneIndex", phoneIndex)
.getSingleResult();

17.8.9. Implicit joins involving collections

The functions element(), index(), key(), and value() may even be applied to a path expression to express an implicit join.

// implicit join to a map value()
List<Call> calls = entityManager.createQuery(
	"select value(ph.callHistory) " +
	"from Phone ph " +
	"where ph.id = :id ",
	Call.class)
.setParameter("id", id)
.getResultList();

// implicit join to a map key()
List<LocalDateTime> timestamps = entityManager.createQuery(
	"select key(ph.callHistory) " +
	"from Phone ph " +
	"where ph.id = :id ",
	LocalDateTime.class)
.setParameter("id", id)
.getResultList();

An element of an indexed collection (an array, list, or map) may even be identified using the index operator:

// indexed lists
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.phones[0].type = LAND_LINE",
	Person.class)
.getResultList();

// maps
List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where p.addresses['HOME'] = :address",
	Person.class)
.setParameter("address", address)
.getResultList();

//max index in list
List<Person> persons = entityManager.createQuery(
	"select pr " +
	"from Person pr " +
	"where pr.phones[max(indices(pr.phones))].type = 'LAND_LINE'",
	Person.class)
.getResultList();

17.9. Projection: select

The select list identifies which objects and values to return as the query results.

This operation is called projection.

Any of the expression types discussed in Expressions may occur in the projection list, unless otherwise noted.

If a query has no explicit select list, the projection is inferred from the entities and joins occurring in the from clause, together with the result type specified by the call to createQuery(). It’s better to specify the projection explicitly, except in the simplest cases.

There might be multiple items in a projection list, in which case each query result is a tuple, and this poses a problem: Java doesn’t have a good way to represent tuples.

If there’s just one projected item in the select list, then, no sweat, that’s the type of each query result. There’s no need to bother with trying to represent a "tuple of length 1".

But if there are multiple expressions in the select list then:

  • by default, each query result is packaged as an array of type Object[], or

  • if explicitly requested by passing the class Tuple to createQuery(), the query result is packaged as an instance of jakarta.persistence.Tuple.

List<Object[]> results = entityManager.createQuery(
	"select p.name, p.nickName " +
	"from Person p ",
	Object[].class
).getResultList();
for (Object[] result : results) {
	String name = (String) result[0];
	String nickName = (String) result[1];
}

List<Tuple> tuples = entityManager.createQuery(
	"select p.name as name, p.nickName as nickName " +
	"from Person p ",
	Tuple.class
).getResultList();
for (Tuple tuple : tuples) {
	String name = tuple.get("name", String.class);
	String nickName = tuple.get("nickName", String.class);
}

The names of the Tuple elements are determined by the aliases given to the projected items in the select list. If no aliases are specified, the elements may be accessed by their position in the list (positions are numbered from 0).

Unfortunately, neither Object[] nor Tuple lets us access an individual item in a result tuple of an HQL query without explicitly specifying the type of the item. (Using a typecast in the case of Object[], or by passing the class object to get() in the case of Tuple.) But there’s another option, as we’re about to see.

Simplifying slightly, the BNF for a projected item is:

(expression | instantiation) alias?

instantiation
    : "NEW" instantiationTarget "(" instantiationArguments ")"

alias
    : "AS"? IDENTIFIER

where instantiatiationArgs is essentially a nested projection list.

So there’s a special expression type that’s only legal in the select clause: the instantiation rule in the BNF above. Let’s see what it does.

17.9.1. select new

The select new construct packages the query results into a user-written Java class instead of an array.

public class CallStatistics {

    private final long count;
    private final long total;
    private final int min;
    private final int max;
    private final double avg;

    public CallStatistics(long count, long total, int min, int max, double avg) {
        this.count = count;
        this.total = total;
        this.min = min;
        this.max = max;
        this.avg = avg;
    }

    //Getters and setters omitted for brevity
}

CallStatistics callStatistics = entityManager.createQuery(
	"select new org.hibernate.orm.test.hql.CallStatistics(" +
	"	count(c), " +
	"	sum(c.duration), " +
	"	min(c.duration), " +
	"	max(c.duration), " +
	"	avg(c.duration)" +
	")  " +
	"from Call c ",
	CallStatistics.class)
.getSingleResult();

The class must be specified by its fully qualified name, and it must have a matching constructor.

This class does not need to be mapped or annotated in any way.

Even if the class is an entity class, the resulting instances are not managed entities and are not associated with the session.

Alternatively, using the syntax select new map, the query may specify that each result should be packaged as a map:

List<Map> phoneCallTotalDurations = entityManager.createQuery(
	"select new map(" +
	"	p.number as phoneNumber , " +
	"	sum(c.duration) as totalDuration, " +
	"	avg(c.duration) as averageDuration " +
	")  " +
	"from Call c " +
	"join c.phone p " +
	"group by p.number ",
	Map.class)
.getResultList();

The keys of the map are determined by the aliases given to the projected items in the select list. If no aliases are specified, the key of an item is its position in the list (positions are numbered from 0).

Or, using the syntax select new list, the query may specify that each result should be packaged as a list:

List<List> phoneCallDurations = entityManager.createQuery(
	"select new list(" +
	"	p.number, " +
	"	c.duration " +
	")  " +
	"from Call c " +
	"join c.phone p ",
	List.class)
.getResultList();

This is an older syntax, that predates JPQL. In hindsight, it’s hard to see what advantage List<Object> offers compared to Object[]. On the other hand, Map is a perfectly fine alternative Tuple, but isn’t portable to other persistence providers.

17.9.2. distinct

The distinct keyword helps remove duplicate results from the query result list. It’s only effect is to add distinct to the generated SQL.

List<String> lastNames = entityManager.createQuery(
	"select distinct p.lastName " +
	"from Person p", String.class)
.getResultList();

As of Hibernate 6, duplicate results arising from the use of join fetch are automatically removed by Hibernate in memory, after reading the database results and materializing entity instances as Java objects. It’s no longer necessary to remove duplicate results explicitly, and, in particular, distinct should not be used for this purpose.

17.9.3. Aggregate functions

It’s common to have aggregate functions like count(), sum(), and max() in a select list. Aggregate functions are special functions that reduce the size of the result set.

The standard aggregate functions defined in both ANSI SQL and JPQL are:

Aggregate function Argument type Result type JPA standard / ANSI SQL standard

count(), including count(distinct), count(all), and count(*)

Any

Long

✓/✓

avg()

Any numeric type

Double

✓/✓

min()

Any numeric type, or string

Same as the argument type

✓/✓

max()

Any numeric type, or string

Same as the argument type

✓/✓

sum()

Any numeric type

See table below

✓/✓

var_pop(), var_samp()

Any numeric type

Double

✗/✓

stddev_pop(), stddev_samp()

Any numeric type

Double

✗/✓

In the case of sum(), the rules for assigning a result type are:

Argument type Result type

Any integral numeric type except BigInteger

Long

Any floating point numeric type

Double

BigInteger

BigInteger

BigDecimal

BigDecimal

Object[] callStatistics = entityManager.createQuery(
	"select " +
	"	count(c), " +
	"	sum(c.duration), " +
	"	min(c.duration), " +
	"	max(c.duration), " +
	"	avg(c.duration)  " +
	"from Call c ",
	Object[].class)
.getSingleResult();

Long phoneCount = entityManager.createQuery(
	"select count(distinct c.phone) " +
	"from Call c ",
	Long.class)
.getSingleResult();

List<Object[]> callCount = entityManager.createQuery(
	"select p.number, count(c) " +
	"from Call c " +
	"join c.phone p " +
	"group by p.number",
	Object[].class)
.getResultList();

HQL defines the two additional aggregate functions which accept a logical predicate as an argument, for example, every(p.amount < 1000.0).

Aggregate function Argument type Result type JPA standard

any()

Logical predicate

Boolean

every()

Logical predicate

Boolean

Aggregate functions usually appear in the select clause, but control over aggregation is the responsibility of the group by clause, as described below.

17.9.4. Aggregate functions and collections

The elements() and indices() functions we met earlier let us apply aggregate functions to a collection:

New syntax Legacy HQL function Applies to Purpose

max(elements(x))

maxelement(x)

Any collection with sortable elements

The maximum element or map value

min(elements(x))

minelement(x)

Any collection with sortable elements

The minimum element or map value

sum(elements(x))

Any collection with numeric elements

The sum of the elements or map values

avg(elements(x))

Any collection with numeric elements

The average of the elements or map values

max(indices(x))

maxindex(x)

Indexed collections (lists and maps)

The maximum list index or map key

min(indices(x))

minindex(x)

Indexed collections (lists and maps)

The minimum list index or map key

sum(indices(x))

Indexed collections (lists and maps)

The sum of the list indexes or map keys

avg(indices(x))

Indexed collections (lists and maps)

The average of the list indexes or map keys

List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where max(elements(p.calls)) = :call",
	Phone.class)
.setParameter("call", call)
.getResultList();

List<Phone> phones = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"where min(elements(p.calls)) = :call",
	Phone.class)
.setParameter("call", call)
.getResultList();

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"where max(indices(p.phones)) = 0",
	Person.class)
.getResultList();

These operations can almost always be written in another way, without the use of these convenience functions.

17.9.5. filter

All aggregate functions support the inclusion of a filter clause, a sort of mini-where applying a restriction to just one item of the select list:

List<Long> callCount = entityManager.createQuery(
	"select count(c) filter (where c.duration < 30) " +
	"from Call c ",
	Long.class)
.getResultList();
List<Object[]> callCount = entityManager.createQuery(
	"select p.number, count(c) filter (where c.duration < 30) " +
	"from Call c " +
	"join c.phone p " +
	"group by p.number",
	Object[].class)
.getResultList();

17.9.6. Ordered set aggregate functions: within group

An ordered set aggregate function is a special aggregate function which has:

  • not only an optional filter clause, as above, but also

  • a within group clause containing a mini-order by specification.

There are two main types of ordered set aggregate function:

  • an inverse distribution function calculates a value that characterizes the distribution of values within the group, for example, percentile_cont(0.5) is the median, and percentile_cont(0.25) is the lower quartile.

  • a hypothetical set function determines the position of a "hypothetical" value within the ordered set of values.

The following ordered set aggregate functions are available on many platforms:

Type Functions

Inverse distribution functions

mode(), percentile_cont(), percentile_disc()

Hypothetical set functions

rank(), dense_rank(), percent_rank(), cume_dist()

Other

listagg(), array_agg

Actually, the most widely-supported ordered set aggregate function is one which builds a string by concatenating the values within a group. This function has different names on different databases, but HQL abstracts these differences, and—following ANSI SQL—calls it listagg().

List<String> callCount = entityManager.createQuery(
	"select listagg(p.number, ', ') within group (order by p.type,p.number) " +
	"from Phone p " +
	"group by p.person",
	String.class)
.getResultList();

17.9.7. Window functions: over

A window function is one which also has an over clause, which may specify:

  • window frame partitioning, with partition by, which is very similar to group by,

  • ordering, with order by, which defines the order of rows within a window frame, and/or

  • windowing, with range, rows, or groups, which define the bounds of the window frame within a partition.

The default partitioning and ordering is taken from the group by and order by clauses of the query. Every partition runs in isolation, that is, rows can’t leak across partitions.

Like ordered set aggregate functions, window functions may optionally specify filter or within group.

Window functions are similar to aggregate functions in the sense that they compute some value based on a "frame" comprising multiple rows. But unlike aggregate functions, window functions don’t flatten rows within a window frame.

The windowing clause specifies one of the following modes:

  • rows for frame start/end defined by a set number of rows, for example, rows n preceding means that only n preceding rows are part of a frame,

  • range for frame start/end defined by value offsets, for example, range n preceding means a preceding row is part of a frame if the abs(value, lag(value) over(..)) ⇐ N, or

  • groups for frame start/end defined by group offsets, for example, groups n preceding means n preceding peer groups are part of a frame, a peer group being rows with equivalent values for order by expressions.

The frame exclusion clause allows excluding rows around the current row:

  • exclude current row excludes the current row,

  • exclude group excludes rows of the peer group of the current row,

  • exclude ties excludes rows of the peer group of the current row, except the current row, and

  • exclude no others is the default, and does not exclude anything.

Frame clause modes range and groups, as well as frame exclusion modes might not be available on every database.

The default frame is rows between unbounded preceding and current row exclude no others, which means that all rows prior to the "current row" are considered.

The following window functions are available on all major platforms:

Window function Purpose Signature

row_number()

The position of the current row within its frame

row_number()

lead()

The value of a subsequent row in the frame

lead(x), lead(x, i, x)

lag()

The value of a previous row in the frame

lag(x), lag(x, i, x)

first_value()

The value of a first row in the frame

first_value(x)

last_value()

The value of a last row in the frame

last_value(x)

nth_value()

The value of the `n`th row in the frame

nth_value(x, n)

In principle every aggregate or ordered set aggregate function might also be used as a window function, just by specifying over, but not every function is supported on every database.

Window functions and ordered set aggregate functions aren’t available on every database. Even where they are available, support for particular features varies widely between databases. Therefore, we won’t waste time going into further detail here. For more information about the syntax and semantics of these functions, consult the documentation for your dialect of SQL.

17.10. Restriction: where

The where clause restricts the results returned by a select query or limits the scope of an update or delete query.

This operation is usually called selection, but since that term is often confused with the select keyword, and since both projection and selection involve "selecting" things, here we’ll use the less-ambiguous term restriction.

A restriction is nothing more than a single logical expression, a topic we exhausted above in Predicates.

17.11. Aggregation: group by and having

An aggregate query is one with aggregate functions in its projection list.

The group by clause divides the result set into groups, so that a query with aggregate functions in the select list returns not a single result for the whole query, but one result for each group.

In short, grouping controls the effect of aggregation.

A query with aggregation may also have a having clause, a restriction applied to the groups.

17.11.1. Aggregation and grouping: group by

The group by clause looks quite similar to the select clause—it has a list of grouped items, but:

  • if there’s just one item, then the query will have a single result for each unique value of that item, or

  • if there are multiple items, the query will have a result for each unique combination or their values.

The BNF for a grouped item is just:

identifier | INTEGER_LITERAL | expression

Consider the following queries:

Long totalDuration = entityManager.createQuery(
	"select sum(c.duration) " +
	"from Call c ",
	Long.class)
.getSingleResult();

List<Object[]> personTotalCallDurations = entityManager.createQuery(
	"select p.name, sum(c.duration) " +
	"from Call c " +
	"join c.phone ph " +
	"join ph.person p " +
	"group by p.name",
	Object[].class)
.getResultList();

//It's even possible to group by entities!
List<Object[]> personTotalCallDurations = entityManager.createQuery(
	"select p, sum(c.duration) " +
	"from Call c " +
	"join c.phone ph " +
	"join ph.person p " +
	"group by p",
	Object[].class)
.getResultList();

The first query retrieves the complete total over all orders. The second retrieves the total for each customer, after grouping the orders by customer.

17.11.2. Totals and subtotals: rollup and cube

The special functions rollup() and cube() may be used in the group by clause, when supported by the database. The semantics are identical to SQL.

These functions are especially useful for reporting:

  • A group by clause with rollup() is used to produce subtotals and grand totals.

  • A group by clause with cube() allows totals for every combination of columns.

17.11.3. Aggregation and restriction: having

In a grouped query, the where clause applies to the non-aggregated values (it determines which rows will make it into the aggregation). The having clause also restricts results, but it operates on the aggregated values.

In an example above, we retrieved Call duration totals for all persons. If that ended up being too much data to deal with, we might want to restrict the results to focus only on customers with a summed total of more than 1000:

List<Object[]> personTotalCallDurations = entityManager.createQuery(
	"select p.name, sum(c.duration) " +
	"from Call c " +
	"join c.phone ph " +
	"join ph.person p " +
	"group by p.name " +
	"having sum(c.duration) > 1000",
	Object[].class)
.getResultList();

The having clause follows the same rules as the where clause and is also made up of predicates. having is applied after the groupings and aggregations have been done, while the where clause is applied before.

17.12. Operations on result sets: union, intersect, and except

These operators apply not to expressions, but to entire result sets:

  • union and union all,

  • intersect and intersect all, and

  • except and except all.

Just like in SQL, all suppresses the elimination of duplicate results.

List<String> results = entityManager.createQuery(
	"select p.name from Person p " +
	"union " +
	"select p.nickName from Person p where p.nickName is not null",
	String.class
).getResultList();

17.13. Sorting: order by

By default, the results of the query are returned in an arbitrary order.

Imposing an order on a set is called sorting.

A relation (a database table) is a set, and therefore certain particularly dogmatic purists have argued that sorting has no place in the algebra of relations. We think this is more than a bit silly: practical data analysis almost always involves sorting, which is a perfectly well-defined operation.

The order by clause specifies a list of projected items used to sort the results. Each sorted item may be:

  • an attribute of an entity or embeddable class,

  • a more complex expression,

  • the alias of a projected item declared in the select list, or

  • a literal integer indicating the ordinal position of a projected item in the select list.

Of course, in principle, only certain types may be sorted: numeric types, string, and date and time types. But HQL is very permissive here and will allow an expression of almost any type to occur in a sort list. Even the identification variable of an entity with a sortable identifier type may occur as a sorted item.

The JPQL specification requires that every sorted item in the order by clause also occur in the select clause. HQL does not enforce this restriction, but applications desiring database portability should be aware that some databases do.

Therefore, you might wish to avoid the use of complex expressions in the sort list.

The BNF for a sorted item is:

sortExpression sortDirection? nullsPrecedence?

sortExpression
    : identifier | INTEGER_LITERAL | expression

sortDirection
    : "ASC" | "DESC"

nullsPrecedence
    : "NULLS" ("FIRST" | "LAST")

Each sorted item listed in the order by clause may explicitly specify a direction, either:

  • asc for ascending order, or

  • desc for descending order.

If no direction is explicitly specified, the results are returned in ascending order.

Of course, there’s an ambiguity with respect to null values. Therefore, the sorting of null values may also be explicitly specified:

  • nulls first puts null values at the beginning of the result set, and

  • nulls last puts them last.

List<Person> persons = entityManager.createQuery(
	"select p " +
	"from Person p " +
	"order by p.name",
	Person.class)
.getResultList();

List<Object[]> personTotalCallDurations = entityManager.createQuery(
	"select p.name, sum(c.duration) as total " +
	"from Call c " +
	"join c.phone ph " +
	"join ph.person p " +
	"group by p.name " +
	"order by total",
	Object[].class)
.getResultList();

Queries with an ordered result list may have limits or pagination.

17.13.1. Limits and offsets

It’s often useful to place a hard upper limit on the number of results that may be returned by a query. The limit and offset clauses are an alternative to the use of setMaxResults() and setFirstResult() respectively, and also may be used for Pagination and limits.

If the limit or offset is parameterized, it’s much easier to use setMaxResults() or setFirstResult().

The SQL syntax fetch first …​ rows only and fetch next …​ rows only is also allowed.

The BNF is a bit complicated:

limitClause
    : "LIMIT" parameterOrIntegerLiteral

offsetClause
    : "OFFSET" parameterOrIntegerLiteral ("ROW" | "ROWS")?

fetchClause
    : "FETCH" ("FIRST" | "NEXT")
      (parameterOrIntegerLiteral | parameterOrNumberLiteral "%")
      ("ROW" | "ROWS")
      ("ONLY" | "WITH" "TIES")

These two queries are identical:

List<Call> calls1 = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"join c.phone p " +
	"order by p.number " +
	"limit 50",
	Call.class)
.getResultList();

// same thing
List<Call> calls2 = entityManager.createQuery(
	"select c " +
	"from Call c " +
	"join c.phone p " +
	"order by p.number " +
	"fetch first 50 rows only",
	Call.class)
.getResultList();

These are well-defined limits: the number of results returned by the database will be limited to 50, as promised. But not every query is quite so well-behaved.

Limiting certainly isn’t a well-defined relational operation, and must be used with care.

In particular, limits don’t play well with fetch joins.

This next query is accepted by HQL, and no more than 50 results are returned by getResultList(), just as expected:

// don't do this! join fetch should not be used with limit
List<Phone> wrongCalls = entityManager.createQuery(
	"select p " +
	"from Phone p " +
	"join fetch p.calls " +
	"order by p " +
	"limit 50",
	Phone.class)
.getResultList();

However, if you log the SQL executed by Hibernate, you’ll notice something wrong:

select
    p1_0.id,
    c1_0.phone_id,
    c1_0.calls_ORDER,
    c1_0.id,
    c1_0.duration,
    c1_0.payment_id,
    c1_0.call_timestamp,
    p1_0.phone_number,
    p1_0.person_id,
    p1_0.phone_type
from
    Phone p1_0
join
    phone_call c1_0
        on p1_0.id=c1_0.phone_id
order by 1

What happened to the limit clause?

When limits or pagination are combined with a fetch join, Hibernate must retrieve all matching results from the database and apply the limit in memory!

This almost certainly isn’t the behavior you were hoping for, and in general will exhibit terrible performance characteristics.

In the next chapter we’ll see a completely different way to write queries in Hibernate.

17.13.2. With clause

The with clause allows to specify common table expressions (CTEs) which can be imagined like named subqueries. Every uncorrelated subquery can be factored to a CTE in the with clause. The semantics are equivalent.

The with clause offers features beyond naming subqueries though:

  • Specify materialization hints

  • Recursive querying

Materialization hint

The materialization hint MATERIALIZED or NOT MATERIALIZED can be applied to tell the DBMS whether a CTE should or shouldn’t be materialized. Consult the database manual of the respective database for the exact meaning of the hint.

Usually, one can expect that MATERIALIZED will cause the subquery to be executed separately and saved into a temporary table, whereas NOT MATERIALIZED will cause the subquery to be inlined into every use site and considered during optimizations separately.

List<Tuple> calls = entityManager.createQuery(
				"with data as materialized(" +
						"  select p.person as owner, c.payment is not null as payed " +
						"  from Call c " +
						"  join c.phone p " +
						"  where p.number = :phoneNumber" +
						")" +
						"select d.owner, d.payed " +
						"from data d",
				Tuple.class)
		.setParameter("phoneNumber", "123-456-7890")
		.getResultList();
Recursive querying

The main use case for the with clause is to define a name for a subquery, such that this subquery can refer to itself, which ultimately enables recursive querying.

Recursive CTEs must follow a very particular shape, which is

  • Base query part

  • union or union all

  • Recursive query part

List<Tuple> calls = entityManager.createQuery(
				"with paymentConnectedPersons as(" +
						"  select a.owner owner " +
						"  from Account a where a.id = :startId " +
						"  union all" +
						"  select a2.owner owner " +
						"  from paymentConnectedPersons d " +
						"  join Account a on a.owner = d.owner " +
						"  join a.payments p " +
						"  join Account a2 on a2.owner = p.person" +
						")" +
						"select d.owner " +
						"from paymentConnectedPersons d",
				Tuple.class)
		.setParameter("startId", 123L)
		.getResultList();

The base query part represents the initial set of rows. When fetching a tree of data, the base query part usually is the tree root.

The recursive query part is executed again and again until it produces no new rows. The result of such a CTE is the base query part result unioned together with all recursive query part executions. Depending on whether union all or union (distinct) is used, duplicate rows are preserved or not.

Recursive queries additionally can have

  • a search clause to hint the DBMS whether to use breadth or depth first searching

  • a cycle clause to hint the DBMS how to determine that a cycle was reached

Defining the search clause requires specifying a name for an attribute in the set sub-clause, that will be added to the CTE type and allows ordering results according to the search order.

searchClause
: "SEARCH" ("BREADTH"|"DEPTH") "FIRST BY" searchSpecifications "SET" identifier
;

searchSpecifications
: searchSpecification ("," searchSpecification)*
;

searchSpecification
: identifier sortDirection? nullsPrecedence?
;

A DBMS has two possible orders when executing the recursive query part

  • Depth first - handle the newest produced rows by the recursive query part first

  • Breadth first - handle the oldest produced rows by the recursive query part first

List<Tuple> calls = entityManager.createQuery(
				"with paymentConnectedPersons as(" +
						"  select a.owner owner " +
						"  from Account a where a.id = :startId " +
						"  union all" +
						"  select a2.owner owner " +
						"  from paymentConnectedPersons d " +
						"  join Account a on a.owner = d.owner " +
						"  join a.payments p " +
						"  join Account a2 on a2.owner = p.person" +
						") search breadth first by owner set orderAttr " +
						"select d.owner " +
						"from paymentConnectedPersons d",
				Tuple.class)
		.setParameter("startId", 123L)
		.getResultList();

Recursive processing can lead to cycles which might lead to queries executing forever. The cycle clause hints the DBMS which CTE attributes to track for the cycle detection. It requires specifying a name for a cycle mark attribute in the set sub-clause, that will be added to the CTE type and allows detecting if a cycle occurred for a result.

By default, the cycle mark attribute will be set to true when a cycle is detected and false otherwise. The values to use can be explicitly specified through the to and default sub-clauses. Optionally, it’s also possible to specify a cycle path attribute name through the using clause The cycle path attribute can be used to understand the traversal path that lead to a result.

cycleClause
	: "CYCLE" cteAttributes "SET" identifier ("TO" literal "DEFAULT" literal)? ("USING" identifier)?
	;
List<Tuple> calls = entityManager.createQuery(
				"with paymentConnectedPersons as(" +
						"  select a.owner owner " +
						"  from Account a where a.id = :startId " +
						"  union all" +
						"  select a2.owner owner " +
						"  from paymentConnectedPersons d " +
						"  join Account a on a.owner = d.owner " +
						"  join a.payments p " +
						"  join Account a2 on a2.owner = p.person" +
						") cycle owner set cycleMark " +
						"select d.owner, d.cycleMark " +
						"from paymentConnectedPersons d",
				Tuple.class)
		.setParameter("startId", 123L)
		.getResultList();

Hibernate merely translates recursive CTEs but doesn’t attempt to emulate the feature. Therefore, this feature will only work if the database supports recursive CTEs. Hibernate does emulate the search and cycle clauses though if necessary, so you can safely use that.

Note that most modern database versions support recursive CTEs already.

18. Criteria

Criteria queries offer a type-safe alternative to HQL, JPQL and native SQL queries.

Criteria queries are a programmatic, type-safe way to express a query. They are type-safe in terms of using interfaces and classes to represent various structural parts of a query such as the query itself, the select clause, or an order-by, etc. They can also be type-safe in terms of referencing attributes as we will see in a bit. Users of the older Hibernate org.hibernate.Criteria query API will recognize the general approach, though we believe the Jakarta Persistence API to be superior as it represents a clean look at the lessons learned from that API.

Criteria queries are essentially an object graph, where each part of the graph represents an increasing (as we navigate down this graph) more atomic part of the query. The first step in performing a criteria query is building this graph. The jakarta.persistence.criteria.CriteriaBuilder interface is the first thing with which you need to become acquainted with before using criteria queries. Its role is that of a factory for all the individual pieces of the criteria. You obtain a jakarta.persistence.criteria.CriteriaBuilder instance by calling the getCriteriaBuilder() method of either jakarta.persistence.EntityManagerFactory or jakarta.persistence.EntityManager.

The next step is to obtain a jakarta.persistence.criteria.CriteriaQuery. This is accomplished using one of the three methods on jakarta.persistence.criteria.CriteriaBuilder for this purpose:

  • <T> CriteriaQuery<T> createQuery( Class<T> resultClass )

  • CriteriaQuery<Tuple> createTupleQuery()

  • CriteriaQuery<Object> createQuery()

Each serves a different purpose depending on the expected type of the query results.

The chapter 6 (i.e., Criteria API) of the Jakarta Persistence Specification already contains a decent amount of reference material pertaining to the various parts of a criteria query. So rather than duplicate all that content here, let’s instead look at some of the more widely anticipated usages of the API.

18.1. Typed criteria queries

The type of the criteria query (aka the <T>) indicates the expected types in the query result. This might be an entity, an Integer, or any other object.

18.2. Selecting an entity

This is probably the most common form of query. The application wants to select entity instances.

Example 556. Selecting the root entity
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);
criteria.select(root);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<Person> persons = entityManager.createQuery(criteria).getResultList();

The example uses createQuery() passing in the Person class reference as the results of the query will be Person objects.

The call to the CriteriaQuery#select method in this example is unnecessary because root will be the implied selection since we have only a single query root. It was done here only for completeness of an example.

The Person_.name reference is an example of the static form of Jakarta Persistence Metamodel reference. We will use that form exclusively in this chapter.

See Build Tool Integration for details on generating this static metamodel.

18.3. Selecting an expression

The simplest form of selecting an expression is selecting a particular attribute from an entity. But this expression might also represent an aggregation, a mathematical operation, etc.

Example 557. Selecting an attribute
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<String> criteria = builder.createQuery(String.class);
Root<Person> root = criteria.from(Person.class);
criteria.select(root.get(Person_.nickName));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<String> nickNames = entityManager.createQuery(criteria).getResultList();

In this example, the query is typed as java.lang.String because that is the anticipated type of the results (the type of the Person#nickName attribute is java.lang.String). Because a query might contain multiple references to the Person entity, attribute references always need to be qualified. This is accomplished by the Root#get method call.

18.4. Selecting multiple values

There are actually a few different ways to select multiple values using criteria queries. We will explore two options here, but an alternative recommended approach is to use tuples as described in Tuple criteria queries, or consider a wrapper query, see Selecting a wrapper for details.

Example 558. Selecting an array
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class);
Root<Person> root = criteria.from(Person.class);

Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);

criteria.select(builder.array(idPath, nickNamePath));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<Object[]> idAndNickNames = entityManager.createQuery(criteria).getResultList();

Technically this is classified as a typed query, but you can see from handling the results that this is sort of misleading. Anyway, the expected result type here is an array.

The example then uses the array method of jakarta.persistence.criteria.CriteriaBuilder which explicitly combines individual selections into a jakarta.persistence.criteria.CompoundSelection.

Example 559. Selecting an array using multiselect
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class);
Root<Person> root = criteria.from(Person.class);

Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);

criteria.multiselect(idPath, nickNamePath);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<Object[]> idAndNickNames = entityManager.createQuery(criteria).getResultList();

Just as we saw in Selecting an array we have a typed criteria query returning an Object array. Both queries are functionally equivalent. This second example uses the multiselect() method which behaves slightly differently based on the type given when the criteria query was first built, but, in this case, it says to select and return an Object[].

18.5. Selecting a wrapper

Another alternative to Selecting multiple values is to instead select an object that will "wrap" the multiple values. Going back to the example query there, rather than returning an array of [Person#id, Person#nickName], instead declare a class that holds these values and use that as a return object.

Example 560. Selecting a wrapper
public class PersonWrapper {

    private final Long id;

    private final String nickName;

    public PersonWrapper(Long id, String nickName) {
        this.id = id;
        this.nickName = nickName;
    }

    public Long getId() {
        return id;
    }

    public String getNickName() {
        return nickName;
    }
}


CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<PersonWrapper> criteria = builder.createQuery(PersonWrapper.class);
Root<Person> root = criteria.from(Person.class);

Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);

criteria.select(builder.construct(PersonWrapper.class, idPath, nickNamePath));
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<PersonWrapper> wrappers = entityManager.createQuery(criteria).getResultList();

First, we see the simple definition of the wrapper object we will be using to wrap our result values. Specifically, notice the constructor and its argument types. Since we will be returning PersonWrapper objects, we use PersonWrapper as the type of our criteria query.

This example illustrates the use of the jakarta.persistence.criteria.CriteriaBuilder method construct which is used to build a wrapper expression. For every row in the result, we are saying we would like a PersonWrapper instantiated with the remaining arguments by the matching constructor. This wrapper expression is then passed as the select.

18.6. Tuple criteria queries

A better approach to Selecting multiple values is to use either a wrapper (which we just saw in Selecting a wrapper) or using the jakarta.persistence.Tuple contract.

Example 561. Selecting a tuple
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);
Root<Person> root = criteria.from(Person.class);

Path<Long> idPath = root.get(Person_.id);
Path<String> nickNamePath = root.get(Person_.nickName);

criteria.multiselect(idPath, nickNamePath);
criteria.where(builder.equal(root.get(Person_.name), "John Doe"));

List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();

for (Tuple tuple : tuples) {
	Long id = tuple.get(idPath);
	String nickName = tuple.get(nickNamePath);
}

//or using indices
for (Tuple tuple : tuples) {
	Long id = (Long) tuple.get(0);
	String nickName = (String) tuple.get(1);
}

This example illustrates accessing the query results through the jakarta.persistence.Tuple interface. The example uses the explicit createTupleQuery() of jakarta.persistence.criteria.CriteriaBuilder. An alternate approach is to use createQuery( Tuple.class ).

Again we see the use of the multiselect() method, just like in Selecting an array using multiselect. The difference here is that the type of the jakarta.persistence.criteria.CriteriaQuery was defined as jakarta.persistence.Tuple so the compound selections, in this case, are interpreted to be the tuple elements.

The jakarta.persistence.Tuple contract provides three forms of access to the underlying elements:

typed

The Selecting a tuple example illustrates this form of access in the tuple.get( idPath ) and tuple.get( nickNamePath ) calls. This allows typed access to the underlying tuple values based on the jakarta.persistence.TupleElement expressions used to build the criteria.

positional

Allows access to the underlying tuple values based on the position. The simple Object get(int position) form is very similar to the access illustrated in Selecting an array and Selecting an array using multiselect. The <X> X get(int position, Class<X> type form allows typed positional access, but based on the explicitly supplied type which the tuple value must be type-assignable to.

aliased

Allows access to the underlying tuple values based on (optionally) assigned alias. The example query did not apply an alias. An alias would be applied via the alias method on jakarta.persistence.criteria.Selection. Just like positional access, there is both a typed (Object get(String alias)) and an untyped (<X> X get(String alias, Class<X> type)) form.

18.7. FROM clause

A CriteriaQuery object defines a query over one or more entity, embeddable, or basic abstract schema types. The root objects of the query are entities, from which the other types are reached by navigation.

— Java Persistence Specification, section 6.5.2 Query Roots, pg 262

All the individual parts of the FROM clause (roots, joins, paths) implement the jakarta.persistence.criteria.From interface.

18.8. Roots

Roots define the basis from which all joins, paths and attributes are available in the query. A root is always an entity type. Roots are defined and added to the criteria by the overloaded from methods on jakarta.persistence.criteria.CriteriaQuery:

Example 562. Root methods
<X> Root<X> from( Class<X> );

<X> Root<X> from( EntityType<X> );
Example 563. Adding a root example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);

Criteria queries may define multiple roots, the effect of which is to create a Cartesian Product between the newly added root and the others. Here is an example defining a Cartesian Product between Person and Partner entities:

Example 564. Adding multiple roots example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);

Root<Person> personRoot = criteria.from(Person.class);
Root<Partner> partnerRoot = criteria.from(Partner.class);
criteria.multiselect(personRoot, partnerRoot);

Predicate personRestriction = builder.and(
	builder.equal(personRoot.get(Person_.address), address),
	builder.isNotEmpty(personRoot.get(Person_.phones))
);
Predicate partnerRestriction = builder.and(
	builder.like(partnerRoot.get(Partner_.name), prefix),
	builder.equal(partnerRoot.get(Partner_.version), 0)
);
criteria.where(builder.and(personRestriction, partnerRestriction));

List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();

18.9. Joins

Joins allow navigation from other jakarta.persistence.criteria.From to either association or embedded attributes. Joins are created by the numerous overloaded join methods of the jakarta.persistence.criteria.From interface.

Example 565. Join example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Phone> criteria = builder.createQuery(Phone.class);
Root<Phone> root = criteria.from(Phone.class);

// Phone.person is a @ManyToOne
Join<Phone, Person> personJoin = root.join(Phone_.person);
// Person.addresses is an @ElementCollection
Join<Person, String> addressesJoin = personJoin.join(Person_.addresses);

criteria.where(builder.isNotEmpty(root.get(Phone_.calls)));

List<Phone> phones = entityManager.createQuery(criteria).getResultList();

18.10. Fetches

Just like in HQL and JPQL, criteria queries can specify that associated data be fetched along with the owner. Fetches are created by the numerous overloaded fetch methods of the jakarta.persistence.criteria.From interface.

Example 566. Join fetch example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Phone> criteria = builder.createQuery(Phone.class);
Root<Phone> root = criteria.from(Phone.class);

// Phone.person is a @ManyToOne
Fetch<Phone, Person> personFetch = root.fetch(Phone_.person);
// Person.addresses is an @ElementCollection
Fetch<Person, String> addressesJoin = personFetch.fetch(Person_.addresses);

criteria.where(builder.isNotEmpty(root.get(Phone_.calls)));

List<Phone> phones = entityManager.createQuery(criteria).getResultList();

Technically speaking, embedded attributes are always fetched with their owner. However, in order to define the fetching of Phone#addresses we needed a jakarta.persistence.criteria.Fetch because element collections are LAZY by default.

18.11. Path expressions

Roots, joins and fetches are themselves path expressions as well.

18.12. Using parameters

Example 567. Parameters example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Person> criteria = builder.createQuery(Person.class);
Root<Person> root = criteria.from(Person.class);

ParameterExpression<String> nickNameParameter = builder.parameter(String.class);
criteria.where(builder.equal(root.get(Person_.nickName), nickNameParameter));

TypedQuery<Person> query = entityManager.createQuery(criteria);
query.setParameter(nickNameParameter, "JD");
List<Person> persons = query.getResultList();

Use the parameter method of jakarta.persistence.criteria.CriteriaBuilder to obtain a parameter reference. Then use the parameter reference to bind the parameter value to the jakarta.persistence.Query.

18.13. Using group by

Example 568. Group by example
CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Tuple> criteria = builder.createQuery(Tuple.class);
Root<Person> root = criteria.from(Person.class);

criteria.groupBy(root.get("address"));
criteria.multiselect(root.get("address"), builder.count(root));

List<Tuple> tuples = entityManager.createQuery(criteria).getResultList();

for (Tuple tuple : tuples) {
	String name = (String) tuple.get(0);
	Long count = (Long) tuple.get(1);
}

19. Criteria extensions

Hibernate ORM provides extensions to the JPA Criteria API to allow making use of HQL features through the Criteria API.

The Session interface gives access to the org.hibernate.query.criteria.HibernateCriteriaBuilder, a subtype of jakarta.persistence.criteria.CriteriaBuilder, through the Session#getCriteriaBuilder() method, which is the entry point to the extensions.

The HibernateCriteriaBuilder interface offers additional methods, but also provides co-variant overridden methods, which return subtypes of that the respective jakarta.persistence.criteria.CriteriaBuilder methods return types. The subtypes are consistently named by prefixing Jpa i.e. Expression becomes JpaExpression.

These subtypes provide additional methods and co-variant overrides to ease working with the extensions.

19.1. Count query creation

A very common requirement is the creation of a count query based on an existing query. This can be done by using the JpaCriteriaQuery#createCountQuery() method.

final HibernateCriteriaBuilder cb = session.getCriteriaBuilder();
final JpaCriteriaQuery<Tuple> cq = cb.createTupleQuery();
final JpaRoot<Contact> root = cq.from( Contact.class );
final JpaParameterExpression<Contact.Gender> parameter = cb.parameter( Contact.Gender.class );

cq.multiselect( root.get( "id" ), root.get( "name" ) );
cq.where( root.get( "gender" ).equalTo( parameter ) );
final Long count = session.createQuery( cq.createCountQuery() )
		.setParameter( parameter, Contact.Gender.FEMALE )
		.getSingleResult();

The resulting count query will wrap a copy of the original query as subquery in the from clause and select count(*).

20. Native SQL Queries

You may also express queries in the native SQL dialect of your database. This is useful if you want to utilize database-specific features such as window functions, Common Table Expressions (CTE) or the CONNECT BY option in Oracle. It also provides a clean migration path from a direct SQL/JDBC based application to Hibernate/Jakarta Persistence. Hibernate also allows you to specify handwritten SQL (including stored procedures) for all create, update, delete, and retrieve operations.

20.1. Creating a native query using Jakarta Persistence

Execution of native SQL queries is controlled via the NativeQuery interface, which is obtained by calling Session.createNativeQuery(). The following sections describe how to use this API for querying.

20.2. Scalar queries

The most basic SQL query is to get a list of scalars (column) values.

Example 569. Jakarta Persistence native query selecting all columns
List<Object[]> persons = entityManager.createNativeQuery(
	"SELECT * FROM Person")
.getResultList();
Example 570. Jakarta Persistence native query with a custom column selection
List<Object[]> persons = entityManager.createNativeQuery(
	"SELECT id, name FROM Person")
.getResultList();

for(Object[] person : persons) {
	Number id = (Number) person[0];
	String name = (String) person[1];
}
Example 571. Hibernate native query selecting all columns
List<Object[]> persons = session.createNativeQuery(
	"SELECT * FROM Person", Object[].class)
.list();
Example 572. Hibernate native query with a custom column selection
List<Object[]> persons = session.createNativeQuery(
	"SELECT id, name FROM Person", Object[].class)
.list();

for(Object[] person : persons) {
	Number id = (Number) person[0];
	String name = (String) person[1];
}

These will return a List of Object arrays ( Object[] ) with scalar values for each column in the PERSON table. Hibernate will use java.sql.ResultSetMetadata to deduce the actual order and types of the returned scalar values.

To avoid the overhead of using ResultSetMetadata, or simply to be more explicit in what is returned, one can use addScalar():

Example 573. Hibernate native query with explicit result set selection
List<Object[]> persons = session.createNativeQuery(
	"SELECT * FROM Person", Object[].class)
.addScalar("id", StandardBasicTypes.LONG)
.addScalar("name", StandardBasicTypes.STRING)
.list();

for(Object[] person : persons) {
	Long id = (Long) person[0];
	String name = (String) person[1];
}

Although it still returns an Object arrays, this query will not use the ResultSetMetadata anymore since it explicitly gets the id and name columns as respectively a BigInteger and a String from the underlying ResultSet. This also means that only these two columns will be returned, even though the query is still using * and the ResultSet contains more than the three listed columns.

It is possible to leave out the type information for all or some of the scalars.

Example 574. Hibernate native query with result set selection that’s a partially explicit
List<Object[]> persons = session.createNativeQuery(
	"SELECT * FROM Person", Object[].class)
.addScalar("id", StandardBasicTypes.LONG)
.addScalar("name")
.list();

for(Object[] person : persons) {
	Long id = (Long) person[0];
	String name = (String) person[1];
}

This is essentially the same query as before, but now ResultSetMetaData is used to determine the type of name, whereas the type of id is explicitly specified.

How the java.sql.Types returned from ResultSetMetaData is mapped to Hibernate types is controlled by the Dialect. If a specific type is not mapped, or does not result in the expected type, it is possible to customize it via calls to registerHibernateType in the Dialect.

20.3. Entity queries

The above queries were all about returning scalar values, basically returning the raw values from the ResultSet.

Example 575. Jakarta Persistence native query selecting entities
List<Person> persons = entityManager.createNativeQuery(
	"SELECT * FROM Person", Person.class)
.getResultList();
Example 576. Hibernate native query selecting entities
List<Person> persons = session.createNativeQuery(
	"SELECT * FROM Person", Person.class)
.list();

Assuming that Person is mapped as a class with the columns id, name, nickName, address, createdOn, and version, the following query will also return a List where each element is a Person entity.

Example 577. Jakarta Persistence native query selecting entities with explicit result set
List<Person> persons = entityManager.createNativeQuery(
	"SELECT id, name, nickName, address, createdOn, version " +
	"FROM Person", Person.class)
.getResultList();
Example 578. Hibernate native query selecting entities with explicit result set
List<Person> persons = session.createNativeQuery(
	"SELECT id, name, nickName, address, createdOn, version " +
	"FROM Person", Person.class)
.list();

20.4. Handling associations and collections

If the entity is mapped with a many-to-one or a child-side one-to-one to another entity, it is required to also return this when performing the native query, otherwise, a database-specific column not found error will occur.

Example 579. Jakarta Persistence native query selecting entities with many-to-one association
List<Phone> phones = entityManager.createNativeQuery(
	"SELECT id, phone_number, phone_type, person_id " +
	"FROM Phone", Phone.class)
.getResultList();
Example 580. Hibernate native query selecting entities with many-to-one association
List<Phone> phones = session.createNativeQuery(
	"SELECT id, phone_number, phone_type, person_id " +
	"FROM Phone", Phone.class)
.list();

This will allow the Phone#person to function properly since the many-to-one or one-to-one association is going to use a proxy that will be initialized when being navigated for the first time.

It is possible to eagerly join the Phone and the Person entities to avoid the possible extra roundtrip for initializing the many-to-one association.

Example 581. Hibernate native query selecting entities with joined many-to-one association
List<Phone> tuples = session.createNativeQuery(
	"SELECT {ph.*}, {pr.*} " +
	"FROM Phone ph " +
	"JOIN Person pr ON ph.person_id = pr.id", Phone.class, "ph")
.addJoin("pr", "ph.person")
.list();

for (Phone phone : tuples) {
	assertNotNull(phone.getPerson().getName());
}
SELECT
    *
FROM
    Phone ph
JOIN
    Person pr
ON  ph.person_id = pr.id

As seen in the associated SQL query, Hibernate manages to construct the entity hierarchy without requiring any extra database roundtrip.

Even when using the addJoin() method, the result list will only contain the root entity. Joined entities will only be present for their respective association.

Example 582. Hibernate native query selecting entities with joined many-to-one association and TupleTransformer
	List<Phone> phones = session.createNativeQuery(
"SELECT {ph.*}, {pr.*} " +
		"FROM Phone ph " +
		"JOIN Person pr ON ph.person_id = pr.id", Phone.class, "ph")
	.addJoin("pr", "ph.person")
	.setTupleTransformer( (TupleTransformer<Phone>) (tuple, aliases) -> (Phone) tuple[0] )
	.list();

	for (Phone person : phones) {
		person.getPerson();
	}

Notice that you added an alias name pr to be able to specify the target property path of the join. It is possible to do the same eager joining for collections (e.g. the Phone#calls one-to-many association).

Example 583. Jakarta Persistence native query selecting entities with joined one-to-many association
List<Phone> phones = entityManager.createNativeQuery(
	"SELECT ph.* " +
	"FROM Phone ph " +
	"JOIN phone_call c ON c.phone_id = ph.id", Phone.class)
.getResultList();

for (Phone phone : phones) {
	List<Call> calls = phone.getCalls();
}
SELECT *
FROM phone ph
JOIN call c ON c.phone_id = ph.id
Example 584. Hibernate native query selecting entities with joined one-to-many association
List<Phone> tuples = session.createNativeQuery(
	"SELECT {ph.*}, {c.*} " +
	"FROM Phone ph " +
	"JOIN phone_call c ON c.phone_id = ph.id", Phone.class, "ph")
.addJoin("c", "ph.calls")
.list();

for (Phone phone : tuples) {
	List<Call> calls = phone.getCalls();
}
SELECT *
FROM phone ph
JOIN call c ON c.phone_id = ph.id

At this stage, you are reaching the limits of what is possible with native queries, without starting to enhance the sql queries to make them usable in Hibernate. Problems can arise when returning multiple entities of the same type or when the default alias/column names are not enough.

20.5. Returning multiple entities

Until now, the result set column names are assumed to be the same as the column names specified in the mapping document. This can be problematic for SQL queries that join multiple tables since the same column names can appear in more than one table.

Column alias injection is needed in the following query which otherwise throws NonUniqueDiscoveredSqlAliasException.

Example 585. Jakarta Persistence native query selecting entities with the same column names
List<Person> entities = entityManager.createNativeQuery(
	"SELECT * " +
	"FROM Person pr, Partner pt " +
	"WHERE pr.name = pt.name", Person.class)
.getResultList();
Example 586. Hibernate native query selecting entities with the same column names
List<Person> entities = session.createNativeQuery(
	"SELECT * " +
	"FROM Person pr, Partner pt " +
	"WHERE pr.name = pt.name", Person.class)
.list();

The query was intended to return all Person and Partner instances with the same name. The query fails because there is a conflict of names since the two entities are mapped to the same column names (e.g. id, name, version). Also, on some databases, the returned column aliases will most likely be on the form pr.id, pr.name, etc. which are not equal to the columns specified in the mappings (id and name).

The following form is not vulnerable to column name duplication:

Example 587. Hibernate native query selecting entities with the same column names and aliases
List<Object> entities = session.createNativeQuery(
	"SELECT {pr.*}, {pt.*} " +
	"FROM Person pr, Partner pt " +
	"WHERE pr.name = pt.name", Object.class)
.addEntity("pr", Person.class)
.addEntity("pt", Partner.class)
.list();

There’s no such equivalent in Jakarta Persistence because the jakarta.persistence.Query interface does not define an addEntity method equivalent.

The {pr.} and {pt.} notation used above is shorthand for "all properties". Alternatively, you can list the columns explicitly, but even in this case, Hibernate injects the SQL column aliases for each property. The placeholder for a column alias is just the property name qualified by the table alias.

20.6. Alias and property references

In most cases, the above alias injection is needed. For queries relating to more complex mappings, like composite properties, inheritance discriminators, collections etc., you can use specific aliases that allow Hibernate to inject the proper aliases.

The following table shows the different ways you can use the alias injection. Please note that the alias names in the result are simply examples, each alias will have a unique and probably different name when used.

Table 5. Alias injection names
Description Syntax Example

A simple property

{[aliasname].[propertyname]}

A_NAME as {item.name}

A composite property

{[aliasname].[componentname].[propertyname]}

CURRENCY as {item.amount.currency}, VALUE as {item.amount.value}

Discriminator of an entity

{[aliasname].class}

DISC as {item.class}

All properties of an entity

{[aliasname].*}

{item.*}

A collection key

{[aliasname].key}

ORGID as {coll.key}

The id of a collection

{[aliasname].id}

EMPID as {coll.id}

The element of a collection

{[aliasname].element}

XID as {coll.element}

property of the element in the collection

{[aliasname].element.[propertyname]}

NAME as {coll.element.name}

All properties of the element in the collection

{[aliasname].element.*}

{coll.element.*}

All properties of the collection

{[aliasname].*}

{coll.*}

20.7. Returning DTOs (Data Transfer Objects)

It is possible to apply a ResultTransformer to native SQL queries, allowing it to return non-managed entities.

Example 588. Hibernate native query selecting DTOs
public class PersonSummaryDTO {

    private Number id;

    private String name;

    //Getters and setters are omitted for brevity

    public Number getId() {
        return id;
    }

    public void setId(Number id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

List<PersonSummaryDTO> dtos = session.createNativeQuery(
	"SELECT p.id as \"id\", p.name as \"name\" " +
	"FROM Person p", Tuple.class)
.setTupleTransformer(
		(tuple, aliases) -> {
			PersonSummaryDTO dto = new PersonSummaryDTO();
			dto.setId( (Long)tuple[0] );
			dto.setName( (String)tuple[1] );
			return dto;
		}
)
.list();

There’s no such equivalent in Jakarta Persistence because the jakarta.persistence.Query interface does not define a setResultTransformer method equivalent.

When materializing a native query result as a polymorphic entity, it is important to understand that both the JOINED as well as the TABLE_PER_CLASS inheritance strategies require that the native query also include a special clazz_ select item, which returns the subclass id that Hibernate needs to determine the concrete Java type for a row.

The subclass id is determined based on some order and the base class of the entity hierarchy has the number 0.

Refer to the respective sections in the inheritance chapter for examples of this.

The above query will return a list of PersonSummaryDTO which has been instantiated and injected the values of id and name into its corresponding properties or fields.

20.8. Handling inheritance

Native SQL queries which query for entities that are mapped as part of an inheritance must include all properties for the base class and all its subclasses.

Example 589. Hibernate native query selecting subclasses
List<CreditCardPayment> payments = session.createNativeQuery(
	"SELECT * " +
	"FROM Payment p " +
	"JOIN CreditCardPayment cp on cp.id = p.id", CreditCardPayment.class)
.list();

There’s no such equivalent in Jakarta Persistence because the jakarta.persistence.Query interface does not define an addEntity method equivalent.

20.9. Parameters

Native SQL queries support ordinal as well as named parameters:

Example 590. Jakarta Persistence native query with parameters
List<Person> persons = entityManager.createNativeQuery(
	"SELECT * " +
	"FROM Person " +
	"WHERE name like :name", Person.class)
.setParameter("name", "J%")
.getResultList();
Example 591. Hibernate native query with parameters
List<Person> persons = session.createNativeQuery(
	"SELECT * " +
	"FROM Person " +
	"WHERE name like :name", Person.class)
.setParameter("name", "J%")
.list();

20.10. Named SQL queries

Named SQL queries can also be defined during mapping and called in exactly the same way as a named HQL query. In this case, you do not need to call addEntity() anymore.

Jakarta Persistence defines the jakarta.persistence.NamedNativeQuery annotation for this purpose, and the Hibernate org.hibernate.annotations.NamedNativeQuery annotation extends it and adds the following attributes:

flushMode()

The flush mode for the query. By default, it uses the current Persistence Context flush mode.

cacheable()

Whether the query (results) is cacheable or not. By default, queries are not cached.

cacheRegion()

If the query results are cacheable, name the query cache region to use.

fetchSize()

The number of rows fetched by the JDBC Driver per database trip. The default value is given by the JDBC driver.

timeout()

The query timeout (in seconds). By default, there’s no timeout.

callable()

Does the SQL query represent a call to a procedure/function? The default is false.

comment()

A comment added to the SQL query for tuning the execution plan.

cacheMode()

The cache mode used for this query. This refers to entities/collections returned by the query. The default value is CacheModeType.NORMAL.

readOnly()

Whether the results should be read-only. By default, queries are not read-only so entities are stored in the Persistence Context.

20.10.1. Named SQL queries selecting scalar values

To fetch a single column of given table, the named query looks as follows:

Example 592. Single scalar value NamedNativeQuery
@NamedNativeQuery(
		name = "find_person_name",
		query =
				"SELECT name " +
						"FROM Person ",
		resultClass = String.class
)
Example 593. Jakarta Persistence named native query selecting a scalar value
List<String> names = entityManager.createNamedQuery(
	"find_person_name", String.class)
.getResultList();
Example 594. Hibernate named native query selecting a scalar value
List<String> names = session.createNamedQuery(
	"find_person_name", String.class)
.list();

Selecting multiple scalar values is done like this:

Example 595. Multiple scalar values NamedNativeQuery
@NamedNativeQuery(
		name = "find_person_name_and_nickName",
		query =
				"SELECT " +
						"   name, " +
						"   nickName " +
						"FROM Person "
)

Without specifying an explicit result type, Hibernate will assume an Object array:

Example 596. Jakarta Persistence named native query selecting multiple scalar values
List<Object[]> tuples = entityManager.createNamedQuery(
	"find_person_name_and_nickName", Object[].class)
.getResultList();

for(Object[] tuple : tuples) {
	String name = (String) tuple[0];
	String nickName = (String) tuple[1];
}
Example 597. Hibernate named native query selecting multiple scalar values
List<Object[]> tuples = session.createNamedQuery(
	"find_person_name_and_nickName", Object[].class)
.list();

for(Object[] tuple : tuples) {
	String name = (String) tuple[0];
	String nickName = (String) tuple[1];
}

It’s possible to use a DTO to store the resulting scalar values:

Example 598. DTO to store multiple scalar values
public class PersonNames {

	private final String name;

	private final String nickName;

	public PersonNames(String name, String nickName) {
		this.name = name;
		this.nickName = nickName;
	}

	public String getName() {
		return name;
	}

	public String getNickName() {
		return nickName;
	}
}
Example 599. Multiple scalar values NamedNativeQuery with ConstructorResult
@NamedNativeQuery(
		name = "find_person_name_and_nickName_dto",
		query =
				"select " +
						"   name, " +
						"   nickName " +
						"from Person ",
		resultSetMapping = "name_and_nickName_dto"
)
@SqlResultSetMapping(
		name = "name_and_nickName_dto",
		classes = @ConstructorResult(
				targetClass = PersonNames.class,
				columns = {
						@ColumnResult(name = "name"),
						@ColumnResult(name = "nickName")
				}
		)
)
Example 600. Jakarta Persistence named native query selecting multiple scalar values into a DTO
List<PersonNames> personNames = entityManager.createNamedQuery(
	"find_person_name_and_nickName_dto", PersonNames.class)
.getResultList();
Example 601. Hibernate named native query selecting multiple scalar values into a DTO
List<PersonNames> personNames = session.createNamedQuery(
	"find_person_name_and_nickName_dto", PersonNames.class)
.list();

You can also use the @NamedNativeQuery Hibernate annotation to customize the named query using various configurations such as fetch mode, cacheability, time out interval.

Example 602. Multiple scalar values using ConstructorResult and Hibernate NamedNativeQuery
@NamedNativeQuery(
		name = "get_person_phone_count",
		query = "select pr.name AS name, count(*) AS phoneCount " +
				"from Phone p " +
				"join Person pr ON pr.id = p.person_id " +
				"group BY pr.name",
		resultSetMapping = "person_phone_count",
		timeout = 1,
		readOnly = true
)
@SqlResultSetMapping(
		name = "person_phone_count",
		classes = @ConstructorResult(
				targetClass = PersonPhoneCount.class,
				columns = {
						@ColumnResult(name = "name"),
						@ColumnResult(name = "phoneCount")
				}
		)
)
Example 603. Hibernate NamedNativeQuery named native query selecting multiple scalar values into a DTO
List<PersonPhoneCount> personNames = session.createNamedQuery(
	"get_person_phone_count", PersonPhoneCount.class)
.getResultList();

20.10.2. Named SQL queries selecting entities

Considering the following named query:

Example 604. Single-entity NamedNativeQuery
@NamedNativeQuery(
		name = "find_person_by_name",
		query =
				"select " +
						"   p.id AS \"id\", " +
						"   p.name AS \"name\", " +
						"   p.nickName AS \"nickName\", " +
						"   p.address AS \"address\", " +
						"   p.createdOn AS \"createdOn\", " +
						"   p.version AS \"version\" " +
						"from Person p " +
						"where p.name LIKE :name",
		resultClass = Person.class
)

The result set mapping declares the entities retrieved by this native query. Each field of the entity is bound to an SQL alias (or column name). All fields of the entity including the ones of subclasses and the foreign key columns of related entities have to be present in the SQL query. Field definitions are optional provided that they map to the same column name as the one declared on the class property.

Executing this named native query can be done as follows:

Example 605. Jakarta Persistence named native entity query
List<Person> persons = entityManager.createNamedQuery(
	"find_person_by_name", Person.class)
.setParameter("name", "J%")
.getResultList();
Example 606. Hibernate named native entity query
List<Person> persons = session.createNamedQuery(
	"find_person_by_name", Person.class)
.setParameter("name", "J%")
.list();

To join multiple entities, you need to use a SqlResultSetMapping for each entity the SQL query is going to fetch.

Example 607. Joined-entities NamedNativeQuery
@NamedNativeQuery(
		name = "find_person_with_phones_by_name",
		query =
				"select " +
						"   pr.id AS \"pr.id\", " +
						"   pr.name AS \"pr.name\", " +
						"   pr.nickName AS \"pr.nickName\", " +
						"   pr.address AS \"pr.address\", " +
						"   pr.createdOn AS \"pr.createdOn\", " +
						"   pr.version AS \"pr.version\", " +
						"   ph.id AS \"ph.id\", " +
						"   ph.person_id AS \"ph.person_id\", " +
						"   ph.phone_number AS \"ph.number\", " +
						"   ph.phone_type AS \"ph.type\" " +
						"from Person pr " +
						"join Phone ph ON pr.id = ph.person_id " +
						"where pr.name LIKE :name",
		resultSetMapping = "person_with_phones"
)
@SqlResultSetMapping(
		name = "person_with_phones",
		entities = {
				@EntityResult(
						entityClass = Person.class,
						fields = {
								@FieldResult( name = "id", column = "pr.id" ),
								@FieldResult( name = "name", column = "pr.name" ),
								@FieldResult( name = "nickName", column = "pr.nickName" ),
								@FieldResult( name = "address", column = "pr.address" ),
								@FieldResult( name = "createdOn", column = "pr.createdOn" ),
								@FieldResult( name = "version", column = "pr.version" ),
						}
				),
				@EntityResult(
						entityClass = Phone.class,
						fields = {
								@FieldResult( name = "id", column = "ph.id" ),
								@FieldResult( name = "person", column = "ph.person_id" ),
								@FieldResult( name = "number", column = "ph.number" ),
								@FieldResult( name = "type", column = "ph.type" ),
						}
				)
		}
)
Example 608. Jakarta Persistence named native entity query with joined associations
List<Object[]> tuples = entityManager.createNamedQuery(
	"find_person_with_phones_by_name", Object[].class)
.setParameter("name", "J%")
.getResultList();

for(Object[] tuple : tuples) {
	Person person = (Person) tuple[0];
	Phone phone = (Phone) tuple[1];
}
Example 609. Hibernate named native entity query with joined associations
List<Object[]> tuples = session.createNamedQuery(
	"find_person_with_phones_by_name", Object[].class)
.setParameter("name", "J%")
.list();

for(Object[] tuple : tuples) {
	Person person = (Person) tuple[0];
	Phone phone = (Phone) tuple[1];
}

Finally, if the association to a related entity involves a composite primary key, a @FieldResult element should be used for each foreign key column. The @FieldResult name is composed of the property name for the relationship, followed by a dot ("."), followed by the name or the field or property of the primary key. For this example, the following entities are going to be used:

Example 610. Entity associations with composite keys and named native queries
@Embeddable
public class Dimensions {

    private int length;

    private int width;

    //Getters and setters are omitted for brevity

}

@Embeddable
public class Identity implements Serializable {

    private String firstname;

    private String lastname;

    //Getters and setters are omitted for brevity

    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        final Identity identity = (Identity) o;

        if (!firstname.equals(identity.firstname)) return false;
        if (!lastname.equals(identity.lastname)) return false;

        return true;
    }

    public int hashCode() {
        int result;
        result = firstname.hashCode();
        result = 29 * result + lastname.hashCode();
        return result;
    }
}

@Entity
public class Captain {

    @EmbeddedId
    private Identity id;

    //Getters and setters are omitted for brevity

}

@Entity
@NamedNativeQueries({
    @NamedNativeQuery(name = "find_all_spaceships",
        query =
            "SELECT " +
            "   name as \"name\", " +
            "   model, " +
            "   speed, " +
            "   lname as lastn, " +
            "   fname as firstn, " +
            "   length, " +
            "   width, " +
            "   length * width as surface, " +
            "   length * width * 10 as volume " +
            "FROM SpaceShip",
        resultSetMapping = "spaceship"
   )
})
@SqlResultSetMapping(
    name = "spaceship",
    entities = @EntityResult(
        entityClass = SpaceShip.class,
        fields = {
            @FieldResult(name = "name", column = "name"),
            @FieldResult(name = "model", column = "model"),
            @FieldResult(name = "speed", column = "speed"),
            @FieldResult(name = "captain.id.lastname", column = "lastn"),
            @FieldResult(name = "captain.id.firstname", column = "firstn"),
            @FieldResult(name = "dimensions.length", column = "length"),
            @FieldResult(name = "dimensions.width", column = "width"),
        }
   ),
    columns = {
        @ColumnResult(name = "surface"),
        @ColumnResult(name = "volume")
    }
)
public class SpaceShip {

    @Id
    private String name;

    private String model;

    private double speed;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "fname", referencedColumnName = "firstname")
    @JoinColumn(name = "lname", referencedColumnName = "lastname")
    private Captain captain;

    private Dimensions dimensions;

    //Getters and setters are omitted for brevity

}
Example 611. Jakarta Persistence named native entity query with joined associations and composite keys
List<Object[]> tuples = entityManager.createNamedQuery(
	"find_all_spaceships", Object[].class)
.getResultList();

for(Object[] tuple : tuples) {
	SpaceShip spaceShip = (SpaceShip) tuple[0];
	Number surface = (Number) tuple[1];
	Number volume = (Number) tuple[2];
}
Example 612. Hibernate named native entity query with joined associations and composite keys
List<Object[]> tuples = session.createNamedQuery(
	"find_all_spaceships", Object[].class)
.list();

for(Object[] tuple : tuples) {
	SpaceShip spaceShip = (SpaceShip) tuple[0];
	Number surface = (Number) tuple[1];
	Number volume = (Number) tuple[2];
}

20.11. Resolving global catalog and schema in native SQL queries

When using multiple database catalogs and schemas, Hibernate offers the possibility of setting a global catalog or schema so that you don’t have to declare it explicitly for every entity.

Example 613. Setting global catalog and schema
<property name="hibernate.default_catalog" value="crm"/>
<property name="hibernate.default_schema" value="analytics"/>

This way, we can imply the global crm catalog and analytics schema in every JPQL, HQL or Criteria API query.

However, for native queries, the SQL query is passed as is, therefore you need to explicitly set the global catalog and schema whenever you are referencing a database table. Fortunately, Hibernate allows you to resolve the current global catalog and schema using the following placeholders:

{h-catalog}

resolves the current hibernate.default_catalog configuration property value.

{h-schema}

resolves the current hibernate.default_schema configuration property value.

{h-domain}

resolves the current hibernate.default_catalog and hibernate.default_schema configuration property values (e.g. catalog.schema).

With these placeholders, you can imply the catalog, schema, or both catalog and schema for every native query.

So, when running the following native query:

@NamedNativeQuery(
    name = "last_30_days_hires",
    query =
        "select * " +
        "from {h-domain}person " +
        "where age(hired_on) < '30 days'",
    resultClass = Person.class
)

Hibernate is going to resolve the {h-domain} placeholder according to the values of the default catalog and schema:

SELECT *
FROM   crm.analytics.person
WHERE  age(hired_on) < '30 days'

20.12. Using stored procedures for querying

Hibernate provides support for queries via stored procedures and functions. A stored procedure arguments are declared using the IN parameter type, and the result can be either marked with an OUT parameter type, a REF_CURSOR or it could just return the result like a function.

Example 614. MySQL stored procedure with OUT parameter type
statement.executeUpdate(
		"CREATE PROCEDURE sp_count_phones (" +
				"   IN personId INT, " +
				"   OUT phoneCount INT " +
				") " +
				"BEGIN " +
				"    SELECT COUNT(*) INTO phoneCount " +
				"    FROM Phone p " +
				"    WHERE p.person_id = personId; " +
				"END"
);

To use this stored procedure, you can execute the following Jakarta Persistence query:

Example 615. Calling a MySQL stored procedure with OUT parameter type using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery( "sp_count_phones" );
query.registerStoredProcedureParameter( "personId", Long.class, ParameterMode.IN );
query.registerStoredProcedureParameter( "phoneCount", Long.class, ParameterMode.OUT );

query.setParameter( "personId", 1L );

query.execute();
Long phoneCount = (Long) query.getOutputParameterValue( "phoneCount" );
Example 616. Calling a MySQL stored procedure with OUT parameter type using Hibernate
Session session = entityManager.unwrap( Session.class );

ProcedureCall call = session.createStoredProcedureCall( "sp_count_phones" );
ProcedureParameter<Long> parameter = call.registerParameter( "personId", Long.class, ParameterMode.IN );
call.setParameter( parameter, 1L );
call.registerParameter( "phoneCount", Long.class, ParameterMode.OUT );

Long phoneCount = (Long) call.getOutputs().getOutputParameterValue( "phoneCount" );
assertEquals( Long.valueOf( 2 ), phoneCount );

If the stored procedure outputs the result directly without an OUT parameter type:

Example 617. MySQL stored procedure without an OUT parameter type
statement.executeUpdate(
		"CREATE PROCEDURE sp_phones(IN personId INT) " +
				"BEGIN " +
				"    SELECT *  " +
				"    FROM Phone   " +
				"    WHERE person_id = personId;  " +
				"END"
);

You can retrieve the results of the aforementioned MySQL stored procedure as follows:

Example 618. Calling a MySQL stored procedure and fetching the result set without an OUT parameter type using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery( "sp_phones" );
query.registerStoredProcedureParameter( 1, Long.class, ParameterMode.IN );

query.setParameter( 1, 1L );

List<Object[]> personComments = query.getResultList();
Example 619. Calling a MySQL stored procedure and fetching the result set without an OUT parameter type using Hibernate
Session session = entityManager.unwrap( Session.class );

ProcedureCall call = session.createStoredProcedureCall( "sp_phones" );
ProcedureParameter<Long> parameter = call.registerParameter( 1, Long.class, ParameterMode.IN );
call.setParameter( parameter, 1L );

Output output = call.getOutputs().getCurrent();

List<Object[]> personComments = ( (ResultSetOutput) output ).getResultList();

For a REF_CURSOR result sets, we’ll consider the following Oracle stored procedure:

Example 620. Oracle REF_CURSOR stored procedure
statement.executeUpdate(
    "CREATE OR REPLACE PROCEDURE sp_person_phones (" +
    "   personId IN NUMBER, " +
    "   personPhones OUT SYS_REFCURSOR) " +
    "AS  " +
    "BEGIN " +
    "    OPEN personPhones FOR " +
    "    SELECT *" +
    "    FROM phone " +
    "    WHERE person_id = personId; " +
    "END;"
);

REF_CURSOR result sets are only supported by some relational databases (e.g. Oracle and PostgreSQL), and other database systems JDBC drivers might not support this feature.

This function can be called using the standard Java Persistence API:

Example 621. Calling an Oracle REF_CURSOR stored procedure using Jakarta Persistence
StoredProcedureQuery query = entityManager.createStoredProcedureQuery("sp_person_phones");
query.registerStoredProcedureParameter(1, Long.class, ParameterMode.IN);
query.registerStoredProcedureParameter(2, Class.class, ParameterMode.REF_CURSOR);
query.setParameter(1, 1L);

query.execute();
List<Object[]> postComments = query.getResultList();
Example 622. Calling an Oracle REF_CURSOR stored procedure using Hibernate
Session session = entityManager.unwrap(Session.class);

ProcedureCall call = session.createStoredProcedureCall("sp_person_phones");
ProcedureParameter<Long> parameter = call.registerParameter(1, Long.class, ParameterMode.IN);
call.setParameter(parameter, 1L);
call.registerParameter(2, Class.class, ParameterMode.REF_CURSOR);

Output output = call.getOutputs().getCurrent();
List<Object[]> postComments = ((ResultSetOutput) output).getResultList();
assertEquals(2, postComments.size());

If the database defines an SQL function:

Example 623. MySQL function
statement.executeUpdate(
		"CREATE FUNCTION fn_count_phones(personId integer)  " +
				"RETURNS integer " +
				"DETERMINISTIC " +
				"READS SQL DATA " +
				"BEGIN " +
				"    DECLARE phoneCount integer; " +
				"    SELECT COUNT(*) INTO phoneCount " +
				"    FROM Phone p " +
				"    WHERE p.person_id = personId; " +
				"    RETURN phoneCount; " +
				"END"
);

Because the current StoredProcedureQuery implementation doesn’t yet support SQL functions, we need to use the JDBC syntax.

This limitation is acknowledged and will be addressed by the HHH-10530 issue.

Example 624. Calling a MySQL function
final AtomicReference<Integer> phoneCount = new AtomicReference<>();
Session session = entityManager.unwrap( Session.class );
session.doWork( connection -> {
	try (CallableStatement function = connection.prepareCall(
			"{ ? = call fn_count_phones(?) }" )) {
		function.registerOutParameter( 1, Types.INTEGER );
		function.setInt( 2, 1 );
		function.execute();
		phoneCount.set( function.getInt( 1 ) );
	}
} );

Stored procedure queries cannot be paged with setFirstResult()/setMaxResults().

Since these servers can return multiple result sets and update counts, Hibernate will iterate the results and take the first result that is a result set as its return value, so everything else will be discarded.

For SQL Server, if you can enable SET NOCOUNT ON in your procedure it will probably be more efficient, but this is not a requirement.

20.13. Using named queries to call stored procedures

Just like with SQL statements, you can also use named queries to call stored procedures. For this purpose, Jakarta Persistence defines the @NamedStoredProcedureQuery annotation.

Example 625. Oracle REF_CURSOR named query stored procedure
@NamedStoredProcedureQuery(
		name = "sp_person_phones",
		procedureName = "sp_person_phones",
		parameters = {
				@StoredProcedureParameter(
						name = "personId",
						type = Long.class,
						mode = ParameterMode.IN
				),
				@StoredProcedureParameter(
						name = "personPhones",
						type = Class.class,
						mode = ParameterMode.REF_CURSOR
				)
		}
)

Calling this stored procedure is straightforward, as illustrated by the following example.

Example 626. Calling an Oracle REF_CURSOR stored procedure using a Jakarta Persistence named query
List<Object[]> postComments = entityManager
.createNamedStoredProcedureQuery("sp_person_phones")
.setParameter("personId", 1L)
.getResultList();

20.14. Custom SQL for CRUD (Create, Read, Update and Delete)

Hibernate can use custom SQL for CRUD operations. The SQL can be overridden at the statement level or individual column level. This section describes statement overrides. For columns, see Column transformers: read and write expressions.

The following example shows how to define custom SQL operations using annotations. @SQLInsert, @SQLUpdate, and @SQLDelete override the INSERT, UPDATE, DELETE statements of a given entity. Similarly, @SQLSelect specifies a custom SELECT query used for loading the underlying table record.

For collections, Hibernate allows defining a custom @SQLDeleteAll which is used for removing all child records associated with a given parent entity. To filter collections, the @SQLRestriction annotation allows customizing the underlying SQL WHERE clause.

Example 627. Custom CRUD
@Entity(name = "Person")
@SQLInsert(
	sql = "INSERT INTO person (name, id, valid) VALUES (?, ?, true) ",
	check = ResultCheckStyle.COUNT
)
@SQLUpdate(
	sql = "UPDATE person SET name = ? where id = ? "
)
@SQLDelete(
	sql = "UPDATE person SET valid = false WHERE id = ? "
)
@SQLSelect(
	sql ="SELECT id, name FROM person WHERE id = ? and valid = true"
)
public static class Person {

	@Id
	@GeneratedValue
	private Long id;

	private String name;

	@ElementCollection
	@SQLInsert(
		sql = "INSERT INTO person_phones (person_id, phones, valid) VALUES (?, ?, true) ")
	@SQLDeleteAll(
		sql = "UPDATE person_phones SET valid = false WHERE person_id = ?")
	@SQLRestriction("valid = true")
	private List<String> phones = new ArrayList<>();

	//Getters and setters are omitted for brevity

}

In the example above, the entity is mapped so that entries are soft-deleted (the records are not removed from the database, but instead, a flag marks the row validity). The Person entity benefits from custom INSERT, UPDATE, and DELETE statements which update the valid column accordingly. The custom @SQLSelect is used to retrieve only Person rows that are valid.

The same is done for the phones collection. The @SQLDeleteAll and the SQLInsert queries are used whenever the collection is modified.

You can also call a store procedure using the custom CRUD statements. The only requirement is to set the callable attribute to true.

To check that the execution happens correctly, Hibernate allows you to define one of those three strategies:

  • none: no check is performed; the store procedure is expected to fail upon constraint violations.

  • count: use of row-count returned by the executeUpdate() method call to check that the update was successful.

  • param: like count but using a CallableStatement output parameter.

To define the result check style, use the check parameter.

The parameter order is important and is defined by the order Hibernate handles properties. You can see the expected order by enabling debug logging, so Hibernate can print out the static SQL that is used to create, update, delete entities.

To see the expected sequence, remember to not include your custom SQL through annotations or mapping files as that will override the Hibernate generated static SQL.

Overriding SQL statements for secondary tables is also possible.

Example 628. Overriding SQL statements for secondary tables
 @Entity(name = "Person")
 @Table(name = "person")
 @SecondaryTable(name = "person_details",
         pkJoinColumns = @PrimaryKeyJoinColumn(name = "person_id"))
 @SQLInsert(
     sql = "INSERT INTO person (name, id, valid) VALUES (?, ?, true) "
)
 @SQLDelete(
     sql = "UPDATE person SET valid = false WHERE id = ? "
 )
 @SQLInsert(
     table = "person_details",
     sql = "INSERT INTO person_details (image, person_id, valid) VALUES (?, ?, true) ",
     check = ResultCheckStyle.COUNT
 )
 @SQLDelete(
     table = "person_details",
     sql = "UPDATE person_details SET valid = false WHERE person_id = ? "
 )

 @Loader(namedQuery = "find_valid_person")
 @NamedNativeQueries({
     @NamedNativeQuery(
         name = "find_valid_person",
         query = "SELECT " +
                 "    p.id, " +
                 "    p.name, " +
                 "    pd.image  " +
                 "FROM person p  " +
                 "LEFT OUTER JOIN person_details pd ON p.id = pd.person_id  " +
                 "WHERE p.id = ? AND p.valid = true AND pd.valid = true",
         resultClass = Person.class
    )
 })
 public static class Person {

     @Id
     @GeneratedValue
     private Long id;

     private String name;

     @Column(name = "image", table = "person_details")
     private byte[] image;

     //Getters and setters are omitted for brevity

 }

The SQL is directly executed in your database, so you can use any dialect you like. This will, however, reduce the portability of your mapping if you use database-specific SQL.

You can also use stored procedures for customizing the CRUD statements.

Assuming the following stored procedure:

Example 629. Oracle stored procedure to soft-delete a given entity
	statement.executeUpdate(
			"CREATE OR REPLACE PROCEDURE sp_delete_person (" +
					"   personId IN NUMBER) " +
					"AS  " +
					"BEGIN " +
					"    UPDATE person SET valid = 0 WHERE id = personId; " +
					"END;"
	);
}

The entity can use this stored procedure to soft-delete the entity in question:

Example 630. Customizing the entity delete statement to use the Oracle stored procedure= instead
@SQLDelete(
		sql = "{ call sp_delete_person(?) } ",
		callable = true
)

You need to set the callable attribute when using a stored procedure instead of an SQL statement.

21. Spatial

21.1. Overview

Hibernate Spatial was originally developed as a generic extension to Hibernate for handling geographic data. Since 5.0, Hibernate Spatial is now part of the Hibernate ORM project, and it allows you to deal with geographic data in a standardized way.

Hibernate Spatial provides a standardized, cross-database interface to geographic data storage and query functions. It supports most of the functions described by the OGC Simple Feature Specification. Supported databases are Oracle 10g/11g, PostgreSQL/PostGIS, MySQL, Microsoft SQL Server, DB2, CockroachDB and H2/GeoDB.

Spatial data types are not part of the Java standard library, and they are absent from the JDBC specification. Over the years JTS has emerged as the de facto standard to fill this gap. JTS is an implementation of the Simple Feature Specification (SFS). Many databases on the other hand implement the SQL/MM - Part 3: Spatial Data specification - a related, but broader specification. The biggest difference is that SFS is limited to 2D geometries in the projected plane (although JTS supports 3D coordinates), whereas SQL/MM supports 2-, 3- or 4-dimensional coordinate spaces.

Hibernate Spatial supports two different geometry models: JTS and geolatte-geom. As already mentioned, JTS is the de facto standard. Geolatte-geom (also written by the lead developer of Hibernate Spatial) is a more recent library that supports many features specified in SQL/MM but not available in JTS (such as support for 4D geometries, and support for extended WKT/WKB formats). Geolatte-geom also implements encoders/decoders for the database native types. Geolatte-geom has good interoperability with JTS. Converting a Geolatte geometry to a JTS geometry, for instance, doesn’t require copying of the coordinates. It also delegates spatial processing to JTS.

Whether you use JTS or Geolatte-geom, Hibernate spatial maps the database spatial types to your geometry model of choice. It will, however, always use Geolatte-geom to decode the database native types.

Hibernate Spatial also makes a number of spatial functions available in HQL and in the Criteria Query API. These functions are specified in both SQL/MM as SFS, and are commonly implemented in databases with spatial support (see Hibernate Spatial dialect function support)

21.2. Configuration

Hibernate Spatial requires some configuration prior to start using it.

21.2.1. Dependency

You need to include the hibernate-spatial dependency in your build environment. For Maven, you need to add the following dependency:

Example 631. Maven dependency
<dependency>
    <groupId>org.hibernate.orm</groupId>
    <artifactId>hibernate-spatial</artifactId>
    <version>${hibernate.version}</version>
</dependency>

Hibernate defines common spatial functions uniformly over all databases. These functions largely correspond to those specified in the Simple Feature Specification. Not all databases are capable of supporting every function, however. The table below details which functions are supported by various database systems.

Table 6. Hibernate Spatial dialect function support

Function

Description

PostgresSQL

Oracle 10g/11g

MySQL

SQLServer

H2GIS

DB2

CockroachDB

Basic functions on Geometry

int st_dimension(Geometry)

SFS §2.1.1.1

String st_geometrytype(Geometry)

SFS §2.1.1.1

int st_srid(Geometry)

SFS §2.1.1.1

Geometry st_envelope(Geometry)

SFS §2.1.1.1

String st_astext(Geometry)

SFS §2.1.1.1

byte[] st_asbinary(Geometry)

SFS §2.1.1.1

boolean st_isempty(Geometry)

SFS §2.1.1.1

boolean st_issimple(Geometry)

SFS §2.1.1.1

Geometry st_boundary(Geometry)

SFS §2.1.1.1

Functions for testing Spatial Relations between geometric objects

boolean st_equals(Geometry, Geometry)

SFS §2.1.1.2

boolean st_disjoint(Geometry, Geometry)

SFS §2.1.1.2

boolean st_intersects(Geometry, Geometry)

SFS §2.1.1.2

boolean st_touches(Geometry, Geometry)

SFS §2.1.1.2

boolean st_crosses(Geometry, Geometry)

SFS §2.1.1.2

boolean st_within(Geometry, Geometry)

SFS §2.1.1.2

boolean st_contains(Geometry, Geometry)

SFS §2.1.1.2

boolean st_overlaps(Geometry, Geometry)

SFS §2.1.1.2

boolean st_relate(Geometry, Geometry, String)

SFS §2.1.1.2

Functions that support Spatial Analysis

double st_distance(Geometry, Geometry)

SFS §2.1.1.3

Geometry st_buffer(Geometry, double)

SFS §2.1.1.3

Geometry st_convexhull(Geometry)

SFS §2.1.1.3

(1)

Geometry st_intersection(Geometry, Geometry)

SFS §2.1.1.3

(1)

Geometry st_geomunion(Geometry, Geometry)

SFS §2.1.1.3 (renamed from union)

(1)

Geometry st_difference(Geometry, Geometry)

SFS §2.1.1.3

(1)

Geometry st_symdifference(Geometry, Geometry)

SFS §2.1.1.3

(1)

Common non-SFS functions

boolean st_dwithin(Geometry, Geometry, double)

Returns true if the geometries are within the specified distance of one another

Geometry st_transform(Geometry, int)

Returns a new geometry with its coordinates transformed to the SRID referenced by the integer parameter

Spatial st_aggregate Functions

Geometry st_extent(Geometry)

Returns a bounding box that bounds the set of returned geometries

(1) Argument Geometries need to have the same dimensionality.

Note that beyond the common spatial functions mentioned above, Hibernate may define additional spatial functions for each database dialect. These will be documented in the Database notes below.

21.3. Database notes

Postgresql

The Postgresql dialect has support for the Postgis spatial extension, but not the Geometric types mentioned in the Postgresql documentation.

In addition to the common spatial functions, the following functions are supported:

Table 7. Additional Postgis function support

Function

Purpose

Syntax

Postgis function operator

distance_2d

2D distance between two geometries

distance_2d(geom,geom)

<->

distance_2d_bbox

2D distance between the bounding boxes of tow geometries

distance_2d_bbox(geom,geom)

<#>

distance_cpa

3D distance between 2 trajectories

distance_cpa(geom,geom)

|=|

distance_centroid_nd

the n-D distance between the centroids of the bounding boxes of two geometries

distance_centroid_nd(geom,geom)

<<->>

MySQL

MySQL versions before 5.6.1 had only limited support for spatial operators. Most operators only took account of the minimum bounding rectangles (MBR) of the geometries, and not the geometries themselves.

This changed in version 5.6.1, when MySQL introduced ST_* spatial operators. The dialect MySQLSpatial56Dialect uses these newer, more precise operators.

For more information, see this page in the MySQL reference guide (esp. the section Functions That Test Spatial Relations Between Geometry Objects)

Oracle10g/11g

There is currently only support for the SDO_GEOMETRY type.

The SDOGeometryType requires access to an OracleConnection object when converting a geometry to SDO_GEOMETRY. In some environments, however, the OracleConnection is not available (e.g. because a Java EE container or connection pool proxy wraps the connection object in its own Connection implementation). A ConnectionFinder knows how to retrieve the OracleConnection from the wrapper or proxy Connection object that is passed into prepared statements. It can be configured with the hibernate.spatial.connection_finder property:

When the passed object is not already an OracleConnection, the default implementation will attempt to retrieve the OracleConnection by recursive reflection. It will search for methods that return Connection objects, execute these methods and check the result. If the result is of type OracleConnection the object is returned. Otherwise, it recurses on it.

In may cases, this strategy will suffice. If not, you can provide your own implementation of this interface on the classpath, and configure it in the hibernate.spatial.connection_finder property. Note that implementations must be thread-safe and have a default no-args constructor.

SQL Server

The GEOGRAPHY type is not currently supported.

CockroachDB

The dialect CockroachDialect supports the GEOMETRY type in CockroachDB v20.2 and later. The GEOGRAPHY type is currently not supported.

H2GIS

The H2Dialect supports H2GIS, a spatial extension of the H2 in-memory database. This dialect can be used as a replacement for the GeoDB dialect that was supported in previous versions. The major difference with GeoDB is that the GEOGRAPHY column type is currently not present in H2GIS.

DB2

The DB2SpatialDialect supports the spatial extensions of the DB2 LUW database. The dialect has been tested with DB2 LUW 11.1. The dialect does not support DB2 for z/OS or DB2 column-oriented databases.

In order to use the DB2 Hibernate Spatial capabilities, it is necessary to first execute the following SQL statements which will allow DB2 to accept Extended WellKnown Text (EWKT) data and return EWKT data. One way to do this is to copy these statements into a file such as ewkt.sql and execute it in a DB2 command window with a command such as db2 -tvf ewkt.sql.

create or replace function db2gse.asewkt(geometry db2gse.st_geometry)
returns clob(2G)
specific db2gse.asewkt1
language sql
deterministic
no external action
reads sql data
return 'srid=' || varchar(db2gse.st_srsid(geometry)) || ';' || db2gse.st_astext(geometry);

create or replace function db2gse.geomfromewkt(instring varchar(32000))
returns db2gse.st_geometry
specific db2gse.fromewkt1
language sql
deterministic
no external action
reads sql data
return db2gse.st_geometry(
substr(instring,posstr(instring,';')+1, length(instring) - posstr(instring,';')),
integer(substr(instring,posstr(instring,'=')+1,posstr(instring,';')-(posstr(instring,'=')+1))));

create transform for db2gse.st_geometry ewkt (
 from sql with function db2gse.asewkt(db2gse.st_geometry),
 to   sql with function db2gse.geomfromewkt(varchar(32000)) );

drop transform db2_program for db2gse.st_geometry;
create transform for db2gse.st_geometry db2_program (
 from sql with function db2gse.asewkt(db2gse.st_geometry),
 to   sql with function db2gse.geomfromewkt(varchar(32000)) );

21.4. Types

It suffices to declare a property as either a JTS or a Geolatte-geom Geometry and Hibernate Spatial will map it using the relevant type.

Here is an example using JTS:

Example 632. Type mapping
import org.locationtech.jts.geom.Point;

@Entity(name = "Event")
public static class Event {

    @Id
    private Long id;

    private String name;

    private Point location;

    //Getters and setters are omitted for brevity
}

We can now treat spatial geometries like any other type.

Example 633. Creating a Point
Event event = new Event();
event.setId( 1L);
event.setName( "Hibernate ORM presentation");
Point point = geometryFactory.createPoint( new Coordinate( 10, 5 ) );
event.setLocation( point );

entityManager.persist( event );

Spatial Dialects defines many query functions that are available both in HQL and JPQL queries. Below we show how we could use the within function to find all objects within a given spatial extent or window.

Example 634. Querying the geometry
Polygon window = geometryFactory.createPolygon( coordinates );
Event event = entityManager.createQuery(
    "select e " +
    "from Event e " +
    "where within(e.location, :window) = true", Event.class)
.setParameter("window", window)
.getSingleResult();

22. Hibernate Vector module

22.1. Overview

The Hibernate ORM Vector module contains support for mathematical vector types and functions. This is useful for AI/ML topics like vector similarity search. The module comes with support for a special vector data type that essentially represents an array of floats.

So far, only the PostgreSQL extension pgvector is supported, but in theory, the vector specific functions could be implemented to work with every database that supports arrays.

For further details, refer to the pgvector documentation.

22.2. Setup

You need to include the hibernate-vector dependency in your build environment. For Maven, you need to add the following dependency:

Example 635. Maven dependency
<dependency>
    <groupId>org.hibernate.orm</groupId>
    <artifactId>hibernate-vector</artifactId>
    <version>${hibernate.version}</version>
</dependency>

The module contains service implementations that are picked up by the Java ServiceLoader automatically, so no further configuration is necessary to make the features available.

22.2.1. Usage

Annotate a persistent attribute with @JdbcTypeCode(SqlTypes.VECTOR) and specify the vector length with @Array(length = …​).

@Column( name = "the_vector" )
@JdbcTypeCode(SqlTypes.VECTOR)
@Array(length = 3)
private float[] theVector;

To cast the string representation of a vector to the vector data type, simply use an HQL cast i.e. cast('[1,2,3]' as vector).

22.2.2. Functions

Expressions of the vector type can be used with various vector functions.

Function Purpose

cosine_distance()

Computes the cosine distance between two vectors. Maps to the <=> operator

euclidean_distance()

Computes the euclidean distance between two vectors. Maps to the <-> operator

l2_distance()

Alias for euclidean_distance()

taxicab_distance()

Computes the taxicab distance between two vectors

l1_distance()

Alias for taxicab_distance()

inner_product()

Computes the inner product between two vectors

negative_inner_product()

Computes the negative inner product. Maps to the <#> operator

vector_dims()

Determines the dimensions of a vector

vector_norm()

Computes the Euclidean norm of a vector

In addition to these special vector functions, it is also possible to use vectors with the following builtin operators

<vector1> + <vector2> = <vector3>

Element-wise addition of vectors.

<vector1> - <vector2> = <vector3>

Element-wise subtraction of vectors.

<vector1> * <vector2> = <vector3>

Element-wise multiplication of vectors.

sum(<vector1>) = <vector2>

Aggregate function support for element-wise summation of vectors.

avg(<vector1>) = <vector2>

Aggregate function support for element-wise average of vectors.

cosine_distance()

Computes the cosine distance between two vectors, which is 1 - inner_product( v1, v2 ) / ( vector_norm( v1 ) * vector_norm( v2 ) ). Maps to the <=> pgvector operator.

final float[] vector = new float[]{ 1, 1, 1 };
final List<Tuple> results = em.createSelectionQuery( "select e.id, cosine_distance(e.theVector, :vec) from VectorEntity e order by e.id", Tuple.class )
		.setParameter( "vec", vector )
		.getResultList();
euclidean_distance() and l2_distance()

Computes the euclidean distance between two vectors, which is sqrt( sum( (v1_i - v2_i)^2 ) ). Maps to the <-> pgvector operator. The l2_distance() function is an alias.

final float[] vector = new float[]{ 1, 1, 1 };
final List<Tuple> results = em.createSelectionQuery( "select e.id, euclidean_distance(e.theVector, :vec) from VectorEntity e order by e.id", Tuple.class )
		.setParameter( "vec", vector )
		.getResultList();
taxicab_distance() and l1_distance()

Computes the taxicab distance between two vectors, which is vector_norm(v1) - vector_norm(v2). The l1_distance() function is an alias.

final float[] vector = new float[]{ 1, 1, 1 };
final List<Tuple> results = em.createSelectionQuery( "select e.id, taxicab_distance(e.theVector, :vec) from VectorEntity e order by e.id", Tuple.class )
		.setParameter( "vec", vector )
		.getResultList();
inner_product() and negative_inner_product()

Computes the inner product between two vectors, which is sum( v1_i * v2_i ). The negative_inner_product() function maps to the <#> pgvector operator, and the inner_product() function as well, but multiplies the result time -1.

final float[] vector = new float[]{ 1, 1, 1 };
final List<Tuple> results = em.createSelectionQuery( "select e.id, inner_product(e.theVector, :vec), negative_inner_product(e.theVector, :vec) from VectorEntity e order by e.id", Tuple.class )
		.setParameter( "vec", vector )
		.getResultList();
vector_dims()

Determines the dimensions of a vector.

final List<Tuple> results = em.createSelectionQuery( "select e.id, vector_dims(e.theVector) from VectorEntity e order by e.id", Tuple.class )
		.getResultList();
vector_norm()

Computes the Euclidean norm of a vector, which is sqrt( sum( v_i^2 ) ).

final List<Tuple> results = em.createSelectionQuery( "select e.id, vector_norm(e.theVector) from VectorEntity e order by e.id", Tuple.class )
		.getResultList();

23. Multitenancy

23.1. What is multitenancy?

The term multitenancy, in general, is applied to software development to indicate an architecture in which a single running instance of an application simultaneously serves multiple clients (tenants). This is highly common in SaaS solutions. Isolating information (data, customizations, etc.) pertaining to the various tenants is a particular challenge in these systems. This includes the data owned by each tenant stored in the database. It is this last piece, sometimes called multitenant data, that we will focus on.

23.2. Multitenant data approaches

There are three main approaches to isolating information in these multitenant systems which go hand-in-hand with different database schema definitions and JDBC setups.

Each multitenancy strategy has pros and cons as well as specific techniques and considerations. Such topics are beyond the scope of this documentation.

23.2.1. Separate database

multitenacy database

Each tenant’s data is kept in a physically separate database instance. JDBC Connections would point specifically to each database so any pooling would be per-tenant. A general application approach, here, would be to define a JDBC Connection pool per-tenant and to select the pool to use based on the tenant identifier associated with the currently logged in user.

23.2.2. Separate schema

multitenacy schema

Each tenant’s data is kept in a distinct database schema on a single database instance. There are two different ways to define JDBC Connections here:

  • Connections could point specifically to each schema as we saw with the Separate database approach. This is an option provided that the driver supports naming the default schema in the connection URL or if the pooling mechanism supports naming a schema to use for its Connections. Using this approach, we would have a distinct JDBC Connection pool per-tenant where the pool to use would be selected based on the "tenant identifier" associated with the currently logged in user.

  • Connections could point to the database itself (using some default schema) but the Connections would be altered using the SQL SET SCHEMA (or similar) command. Using this approach, we would have a single JDBC Connection pool for use to service all tenants, but before using the Connection, it would be altered to reference the schema named by the "tenant identifier" associated with the currently logged in user.

23.2.3. Partitioned (discriminator) data

multitenacy discriminator

All data is kept in a single database schema. The data for each tenant is partitioned by the use of partition value or discriminator. The complexity of this discriminator might range from a simple column value to a complex SQL formula. Again, this approach would use a single Connection pool to service all tenants. However, in this approach, the application needs to alter each and every SQL statement sent to the database to reference the "tenant identifier" discriminator.

23.3. Multitenancy in Hibernate

Using Hibernate with multitenant data comes down to both an API and then integration piece(s). As usual, Hibernate strives to keep the API simple and isolated from any underlying integration complexities. The API is really just defined by passing the tenant identifier as part of opening any session.

Example 636. Specifying tenant identifier from SessionFactory
private void doInSession(String tenant, Consumer<Session> function) {
    Session session = null;
    Transaction txn = null;
    try {
        session = sessionFactory
            .withOptions()
            .tenantIdentifier(tenant)
            .openSession();
        txn = session.getTransaction();
        txn.begin();
        function.accept(session);
        txn.commit();
    } catch (Throwable e) {
        if (txn != null) txn.rollback();
        throw e;
    } finally {
        if (session != null) {
            session.close();
        }
    }
}

23.3.1. @TenantId

For the partitioned data approach, each entity representing partitioned data must declare a field annotated @TenantId.

Example 637. A @TenantId usage example
@Entity
public class Account {

    @Id @GeneratedValue Long id;

    @TenantId String tenantId;

    ...
}

The @TenantId field is automatically populated by Hibernate when an instance is made persistent.

23.3.2. MultiTenantConnectionProvider

When using either the separate database or separate schema approach, Hibernate needs to be able to obtain connections in a tenant-specific manner.

That is the role of the MultiTenantConnectionProvider contract. Application developers will need to provide an implementation of this contract.

Most of its methods are extremely self-explanatory. The only ones which might not be are getAnyConnection and releaseAnyConnection. It is important to note also that these methods do not accept the tenant identifier. Hibernate uses these methods during startup to perform various configuration, mainly via the java.sql.DatabaseMetaData object.

The MultiTenantConnectionProvider to use can be specified in a number of ways:

  • Use the hibernate.multi_tenant_connection_provider setting. It could name a MultiTenantConnectionProvider instance, a MultiTenantConnectionProvider implementation class reference or a MultiTenantConnectionProvider implementation class name.

  • Passed directly to the org.hibernate.boot.registry.StandardServiceRegistryBuilder.

  • If none of the above options match, but the settings do specify a hibernate.connection.datasource value, Hibernate will assume it should use the specific DataSourceBasedMultiTenantConnectionProviderImpl implementation which works on a number of pretty reasonable assumptions when running inside of an app server and using one javax.sql.DataSource per tenant. See its Javadocs for more details.

The following example portrays a MultiTenantConnectionProvider implementation that handles multiple ConnectionProviders.

Example 638. A MultiTenantConnectionProvider implementation
public class ConfigurableMultiTenantConnectionProvider
        extends AbstractMultiTenantConnectionProvider<String> {

    private final Map<String, ConnectionProvider> connectionProviderMap =
        new HashMap<>();

    public ConfigurableMultiTenantConnectionProvider(
            Map<String, ConnectionProvider> connectionProviderMap) {
        this.connectionProviderMap.putAll(connectionProviderMap);
    }

    @Override
    protected ConnectionProvider getAnyConnectionProvider() {
        return connectionProviderMap.values().iterator().next();
    }

    @Override
    protected ConnectionProvider selectConnectionProvider(String tenantIdentifier) {
        return connectionProviderMap.get(tenantIdentifier);
    }
}

The ConfigurableMultiTenantConnectionProvider can be set up as follows:

Example 639. A MultiTenantConnectionProvider usage example
private void init() {
    registerConnectionProvider(FRONT_END_TENANT);
    registerConnectionProvider(BACK_END_TENANT);

    Map<String, Object> settings = new HashMap<>();

    settings.put(AvailableSettings.MULTI_TENANT_CONNECTION_PROVIDER,
        new ConfigurableMultiTenantConnectionProvider(connectionProviderMap));

    sessionFactory = sessionFactory(settings);
}

protected void registerConnectionProvider(String tenantIdentifier) {
    Properties properties = properties();
    properties.put(Environment.URL,
        tenantUrl(properties.getProperty(Environment.URL), tenantIdentifier));

    DriverManagerConnectionProviderImpl connectionProvider =
        new DriverManagerConnectionProviderImpl();
    connectionProvider.configure( PropertiesHelper.map(properties) );
    connectionProviderMap.put(tenantIdentifier, connectionProvider);
}

When using multitenancy, it’s possible to save an entity with the same identifier across different tenants:

Example 640. An example of saving entities with the same identifier across different tenants
doInSession(FRONT_END_TENANT, session -> {
    Person person = new Person();
    person.setId(1L);
    person.setName("John Doe");
    session.persist(person);
});

doInSession(BACK_END_TENANT, session -> {
    Person person = new Person();
    person.setId(1L);
    person.setName("John Doe");
    session.persist(person);
});

23.3.3. CurrentTenantIdentifierResolver

org.hibernate.context.spi.CurrentTenantIdentifierResolver is a contract for Hibernate to be able to resolve what the application considers the current tenant identifier. The implementation to use can be either passed directly to Configuration via its setCurrentTenantIdentifierResolver method, or be specified via the hibernate.tenant_identifier_resolver setting.

There are two situations where CurrentTenantIdentifierResolver is used:

  • The first situation is when the application is using the org.hibernate.context.spi.CurrentSessionContext feature in conjunction with multitenancy. In the case of the current-session feature, Hibernate will need to open a session if it cannot find an existing one in scope. However, when a session is opened in a multitenant environment, the tenant identifier has to be specified. This is where the CurrentTenantIdentifierResolver comes into play; Hibernate will consult the implementation you provide to determine the tenant identifier to use when opening the session. In this case, it is required that a CurrentTenantIdentifierResolver is supplied.

  • The other situation is when you do not want to explicitly specify the tenant identifier all the time. If a CurrentTenantIdentifierResolver has been specified, Hibernate will use it to determine the default tenant identifier to use when opening the session.

Additionally, if the CurrentTenantIdentifierResolver implementation returns true for its validateExistingCurrentSessions method, Hibernate will make sure any existing sessions that are found in scope have a matching tenant identifier. This capability is only pertinent when the CurrentTenantIdentifierResolver is used in current-session settings.

23.3.4. Caching

Multitenancy support in Hibernate works seamlessly with the Hibernate second level cache. The key used to cache data encodes the tenant identifier.

Currently, schema export will not really work with multitenancy.

23.3.5. Multitenancy Hibernate Session configuration

When using multitenancy, you might want to configure each tenant-specific Session differently. For instance, each tenant could specify a different time zone configuration.

Example 641. Registering the tenant-specific time zone information
registerConnectionProvider(FRONT_END_TENANT, TimeZone.getTimeZone("UTC"));
registerConnectionProvider(BACK_END_TENANT, TimeZone.getTimeZone("CST"));

The registerConnectionProvider method is used to define the tenant-specific context.

Example 642. The registerConnectionProvider method used for defining the tenant-specific context
protected void registerConnectionProvider(String tenantIdentifier, TimeZone timeZone) {
    Properties properties = properties();
    properties.put(
        Environment.URL,
        tenantUrl( properties.getProperty(Environment.URL), tenantIdentifier )
   );

    DriverManagerConnectionProviderImpl connectionProvider =
            new DriverManagerConnectionProviderImpl();
    connectionProvider.configure( PropertiesHelper.map(properties) );

    connectionProviderMap.put(tenantIdentifier, connectionProvider);

    timeZoneTenantMap.put(tenantIdentifier, timeZone);
}

For our example, the tenant-specific context is held in the connectionProviderMap and timeZoneTenantMap.

private Map<String, ConnectionProvider> connectionProviderMap = new HashMap<>();

private Map<String, TimeZone> timeZoneTenantMap = new HashMap<>();

Now, when building the Hibernate Session, aside from passing the tenant identifier, we could also configure the Session to use the tenant-specific time zone.

Example 643. The Hibernate Session can be configured using the tenant-specific context
private void doInSession(String tenant, Consumer<Session> function, boolean useTenantTimeZone) {
    Session session = null;
    Transaction txn = null;

    try {
        SessionBuilder sessionBuilder = sessionFactory
                .withOptions()
                .tenantIdentifier(tenant);

        if (useTenantTimeZone) {
            sessionBuilder.jdbcTimeZone(timeZoneTenantMap.get(tenant));
        }

        session = sessionBuilder.openSession();

        txn = session.getTransaction();
        txn.begin();

        function.accept(session);

        txn.commit();
    }
    catch (Throwable e) {
        if (txn != null) {
            txn.rollback();
        }
        throw e;
    }
    finally {
        if (session != null) {
            session.close();
        }
    }
}

So, if we set the useTenantTimeZone parameter to true, Hibernate will persist the Timestamp properties using the tenant-specific time zone. As you can see in the following example, the Timestamp is successfully retrieved even if the currently running JVM uses a different time zone.

Example 644. The useTenantTimeZone allows you to persist a Timestamp in the provided time zone
doInSession(FRONT_END_TENANT, session -> {
    Person person = new Person();
    person.setId(1L);
    person.setName("John Doe");
    person.setCreatedOn(LocalDateTime.of(2018, 11, 23, 12, 0, 0));

    session.persist(person);
}, true);

doInSession(BACK_END_TENANT, session -> {
    Person person = new Person();
    person.setId(1L);
    person.setName("John Doe");
    person.setCreatedOn(LocalDateTime.of(2018, 11, 23, 12, 0, 0));

    session.persist(person);
}, true);

doInSession(FRONT_END_TENANT, session -> {
    Timestamp personCreationTimestamp = (Timestamp) session
    .createNativeQuery(
        "select p.created_on " +
        "from Person p " +
        "where p.id = :personId", Timestamp.class)
    .setParameter("personId", 1L)
    .getSingleResult();

    assertEquals(
        Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)),
        personCreationTimestamp
   );
}, true);

doInSession(BACK_END_TENANT, session -> {
    Timestamp personCreationTimestamp = (Timestamp) session
    .createNativeQuery(
        "select p.created_on " +
        "from Person p " +
        "where p.id = :personId", Timestamp.class)
    .setParameter("personId", 1L)
    .getSingleResult();

    assertEquals(
        Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)),
        personCreationTimestamp
   );
}, true);

However, behind the scenes, we can see that Hibernate has saved the created_on property in the tenant-specific time zone. The following example shows you that the Timestamp was saved in the UTC time zone, hence the offset displayed in the test output.

Example 645. With the useTenantTimeZone property set to false, the Timestamp is fetched in the tenant-specific time zone
doInSession(FRONT_END_TENANT, session -> {
    Timestamp personCreationTimestamp = (Timestamp) session
    .createNativeQuery(
        "select p.created_on " +
        "from Person p " +
        "where p.id = :personId", Timestamp.class)
    .setParameter("personId", 1L)
    .getSingleResult();

    log.infof(
        "The created_on timestamp value is: [%s]",
        personCreationTimestamp
   );

    long timeZoneOffsetMillis =
            Timestamp.valueOf(LocalDateTime.of(2018, 11, 23, 12, 0, 0)).getTime() -
            personCreationTimestamp.getTime();

    assertEquals(
        TimeZone.getTimeZone(ZoneId.systemDefault()).getRawOffset(),
        timeZoneOffsetMillis
   );

    log.infof(
        "For the current time zone: [%s], the UTC time zone offset is: [%d]",
        TimeZone.getDefault().getDisplayName(), timeZoneOffsetMillis
   );
}, false);
SELECT
    p.created_on
FROM
    Person p
WHERE
    p.id = ?

-- binding parameter [1] as [BIGINT] - [1]
-- extracted value ([CREATED_ON] : [TIMESTAMP]) - [2018-11-23 10:00:00.0]

-- The created_on timestamp value is: [2018-11-23 10:00:00.0]
-- For the current time zone: [Eastern European Time], the UTC time zone offset is: [7200000]

Notice that for the Eastern European Time time zone, the time zone offset was 2 hours when the test was executed.

24. Envers

24.1. Basics

To audit changes that are performed on an entity, you only need two things:

  • the hibernate-envers jar on the classpath,

  • an @Audited annotation on the entity.

Unlike in previous versions, you no longer need to specify listeners in the Hibernate configuration file. Just putting the Envers jar on the classpath is enough because listeners will be registered automatically.

And that’s all. You can create, modify and delete the entities as always.

The use of Jakarta Persistence’s CriteriaUpdate and CriteriaDelete bulk operations are not currently supported by Envers due to how an entity’s lifecycle events are dispatched. Such operations should be avoided as they’re not captured by Envers and lead to incomplete audit history.

If you look at the generated schema for your entities, or at the data persisted by Hibernate, you will notice that there are no changes. However, for each audited entity, a new table is introduced - entity_table_AUD, which stores the historical data, whenever you commit a transaction.

Envers automatically creates audit tables if hibernate.hbm2ddl.auto option is set to create, create-drop or update. Appropriate DDL statements can also be generated with an Ant task in Generating Envers schema with Hibernate hbm2ddl tool.

Considering we have a Customer entity, when annotating it with the Audited annotation, Hibernate is going to generate the following tables using the hibernate.hbm2ddl.auto schema tool:

Example 646. Basic Envers entity mapping
@Audited
@Entity(name = "Customer")
public static class Customer {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	@Temporal(TemporalType.TIMESTAMP)
	@Column(name = "created_on")
	@CreationTimestamp
	private Date createdOn;

	//Getters and setters are omitted for brevity

}
create table Customer (
    id bigint not null,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    primary key (id)
)

create table Customer_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    primary key (id, REV)
)

create table REVINFO (
    REV integer generated by default as identity,
    REVTSTMP bigint,
    primary key (REV)
)

alter table Customer_AUD
   add constraint FK5ecvi1a0ykunrriib7j28vpdj
   foreign key (REV)
   references REVINFO

Instead of annotating the whole class and auditing all properties, you can annotate only some persistent properties with @Audited. This will cause only these properties to be audited.

Now, considering the previous Customer entity, let’s see how Envers auditing works when inserting, updating, and deleting the entity in question.

Example 647. Auditing the entity INSERT operation
Customer customer = new Customer();
customer.setId(1L);
customer.setFirstName("John");
customer.setLastName("Doe");

entityManager.persist(customer);
insert
into
    Customer
    (created_on, firstName, lastName, id)
values
    (?, ?, ?, ?)

-- binding parameter [1] as [TIMESTAMP] - [Mon Jul 24 17:21:32 EEST 2017]
-- binding parameter [2] as [VARCHAR]   - [John]
-- binding parameter [3] as [VARCHAR]   - [Doe]
-- binding parameter [4] as [BIGINT]    - [1]

insert
into
    REVINFO
    (REV, REVTSTMP)
values
    (?, ?)

-- binding parameter [1] as [BIGINT]    - [1]
-- binding parameter [2] as [BIGINT]    - [1500906092803]

insert
into
    Customer_AUD
    (REVTYPE, created_on, firstName, lastName, id, REV)
values
    (?, ?, ?, ?, ?, ?)

-- binding parameter [1] as [INTEGER]   - [0]
-- binding parameter [2] as [TIMESTAMP] - [Mon Jul 24 17:21:32 EEST 2017]
-- binding parameter [3] as [VARCHAR]   - [John]
-- binding parameter [4] as [VARCHAR]   - [Doe]
-- binding parameter [5] as [BIGINT]    - [1]
-- binding parameter [6] as [INTEGER]   - [1]
Example 648. Auditing the entity UPDATE operation
Customer customer = entityManager.find(Customer.class, 1L);
customer.setLastName("Doe Jr.");
update
    Customer
set
    created_on=?,
    firstName=?,
    lastName=?
where
    id=?

-- binding parameter [1] as [TIMESTAMP] - [2017-07-24 17:21:32.757]
-- binding parameter [2] as [VARCHAR]   - [John]
-- binding parameter [3] as [VARCHAR]   - [Doe Jr.]
-- binding parameter [4] as [BIGINT]    - [1]

insert
into
    REVINFO
    (REV, REVTSTMP)
values
    (?, ?)

-- binding parameter [1] as [BIGINT]    - [2]
-- binding parameter [2] as [BIGINT]    - [1500906092853]

insert
into
    Customer_AUD
    (REVTYPE, created_on, firstName, lastName, id, REV)
values
    (?, ?, ?, ?, ?, ?)

-- binding parameter [1] as [INTEGER]   - [1]
-- binding parameter [2] as [TIMESTAMP] - [2017-07-24 17:21:32.757]
-- binding parameter [3] as [VARCHAR]   - [John]
-- binding parameter [4] as [VARCHAR]   - [Doe Jr.]
-- binding parameter [5] as [BIGINT]    - [1]
-- binding parameter [6] as [INTEGER]   - [2]
Example 649. Auditing the entity DELETE operation
Customer customer = entityManager.getReference(Customer.class, 1L);
entityManager.remove(customer);
delete
from
    Customer
where
    id = ?

-- binding parameter [1] as [BIGINT]    - [1]

insert
into
    REVINFO
    (REV, REVTSTMP)
values
    (?, ?)

-- binding parameter [1] as [BIGINT]    - [3]
-- binding parameter [2] as [BIGINT]    - [1500906092876]

insert
into
    Customer_AUD
    (REVTYPE, created_on, firstName, lastName, id, REV)
values
    (?, ?, ?, ?, ?, ?)

-- binding parameter [1] as [INTEGER]   - [2]
-- binding parameter [2] as [TIMESTAMP] - [null]
-- binding parameter [3] as [VARCHAR]   - [null]
-- binding parameter [4] as [VARCHAR]   - [null]
-- binding parameter [5] as [BIGINT]    - [1]
-- binding parameter [6] as [INTEGER]   - [3]

The REVTYPE column value is taken from the RevisionType Enum.

Table 8. REVTYPE column values

Database column value

Associated RevisionType Enum value

Description

0

ADD

A database table row was inserted.

1

MOD

A database table row was updated.

2

DEL

A database table row was deleted.

The audit (history) of an entity can be accessed using the AuditReader interface, which can be obtained by having an open EntityManager or Session via the AuditReaderFactory.

Example 650. Getting a list of revisions for the Customer entity
List<Number> revisions = scope.fromTransaction( entityManager -> {
	 return AuditReaderFactory.get(entityManager).getRevisions(
		Customer.class,
		1L
	);
});
select
    c.REV as col_0_0_
from
    Customer_AUD c
cross join
    REVINFO r
where
    c.id = ?
    and c.REV = r.REV
order by
    c.REV asc

-- binding parameter [1] as [BIGINT] - [1]

Using the previously fetched revisions, we can now inspect the state of the Customer entity at that particular revision:

Example 651. Getting the first revision for the Customer entity
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(0))
.getSingleResult();

assertEquals("Doe", customer.getLastName());
select
    c.id as id1_1_,
    c.REV as REV2_1_,
    c.REVTYPE as REVTYPE3_1_,
    c.created_on as created_4_1_,
    c.firstName as firstNam5_1_,
    c.lastName as lastName6_1_
from
    Customer_AUD c
where
    c.REV = (
        select
            max( c_max.REV )
        from
            Customer_AUD c_max
        where
            c_max.REV <= ?
            and c.id = c_max.id
    )
    and c.REVTYPE <> ?

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]

When executing the aforementioned SQL query, there are two parameters:

revision_number

The first parameter marks the revision number we are interested in or the latest one that exists up to this particular revision.

revision_type

The second parameter specifies that we are not interested in DEL RevisionType so that deleted entries are filtered out.

The same goes for the second revision associated with the UPDATE statement.

Example 652. Getting the second revision for the Customer entity
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(1))
.getSingleResult();

assertEquals("Doe Jr.", customer.getLastName());

For the deleted entity revision, Envers throws a NoResultException since the entity was no longer valid at that revision.

Example 653. Getting the third revision for the Customer entity
try {
	Customer customer = (Customer) AuditReaderFactory
	.get(entityManager)
	.createQuery()
	.forEntitiesAtRevision(Customer.class, revisions.get(2))
	.getSingleResult();

	fail("The Customer was deleted at this revision: " + revisions.get(2));
}
catch (NoResultException expected) {
}

You can use the forEntitiesAtRevision(Class<T> cls, String entityName, Number revision, boolean includeDeletions) method to get the deleted entity revision so that, instead of a NoResultException, all attributes, except for the entity identifier, are going to be null.

Example 654. Getting the third revision for the Customer entity without getting a NoResultException
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(
	Customer.class,
	Customer.class.getName(),
	revisions.get(2),
	true)
.getSingleResult();

assertEquals(Long.valueOf(1L), customer.getId());
assertNull(customer.getFirstName());
assertNull(customer.getLastName());
assertNull(customer.getCreatedOn());

See the Javadocs for details on other functionality offered.

24.2. Configuration Properties

It is possible to configure various aspects of Hibernate Envers behavior, such as table names, etc.

org.hibernate.envers.audit_table_prefix

String that will be prepended to the name of an audited entity to create the name of the entity and that will hold audit information.

org.hibernate.envers.audit_table_suffix (default: _AUD)

String that will be appended to the name of an audited entity to create the name of the entity and that will hold audit information.

If you audit an entity with a table name Person, in the default setting Envers will generate a Person_AUD table to store historical data.

org.hibernate.envers.revision_field_name (default: REV)

Name of a field in the audit entity that will hold the revision number.

org.hibernate.envers.revision_type_field_name (default: REVTYPE )

Name of a field in the audit entity that will hold the type of the revision (currently, this can be: add, mod, del).

org.hibernate.envers.revision_on_collection_change (default: true )

Should a revision be generated when a not-owned relation field changes (this can be either a collection in a one-to-many relation or the field using mappedBy attribute in a one-to-one relation).

org.hibernate.envers.do_not_audit_optimistic_locking_field (default: true )

When true, properties to be used for optimistic locking, annotated with @Version, will not be automatically audited (their history won’t be stored; it normally doesn’t make sense to store it).

org.hibernate.envers.store_data_at_delete (default: false )

Should the entity data be stored in the revision when the entity is deleted (instead of only storing the id and all other properties as null).

This is not normally needed, as the data is present in the last-but-one revision. Sometimes, however, it is easier and more efficient to access it in the last revision (then the data that the entity contained before deletion is stored twice).

org.hibernate.envers.default_schema (default: null - same schema as the table being audited)

The default schema name that should be used for audit tables.

Can be overridden using the @AuditTable( schema = "…​" ) annotation.

If not present, the schema will be the same as the schema of the table being audited.

org.hibernate.envers.default_catalog (default: null - same catalog as the table being audited)

The default catalog name that should be used for audit tables.

Can be overridden using the @AuditTable( catalog = "…​" ) annotation.

If not present, the catalog will be the same as the catalog of the normal tables.

org.hibernate.envers.audit_strategy(default: org.hibernate.envers.strategy.DefaultAuditStrategy )

The audit strategy that should be used when persisting audit data. The default stores only the revision, at which an entity was modified.

An alternative, the org.hibernate.envers.strategy.ValidityAuditStrategy stores both the start revision and the end revision. Together these define when an audit row was valid, hence the name ValidityAuditStrategy.

org.hibernate.envers.audit_strategy_validity_end_rev_field_name (default: REVEND)

The column name that will hold the end revision number in audit entities. This property is only valid if the validity audit strategy is used.

org.hibernate.envers.audit_strategy_validity_store_revend_timestamp(default: false )

Should the timestamp of the end revision be stored, until which the data was valid, in addition to the end revision itself. This is useful to be able to purge old Audit records out of a relational database by using table partitioning.

Partitioning requires a column that exists within the table. This property is only evaluated if the ValidityAuditStrategy is used.

org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name(default: REVEND_TSTMP )

Column name of the timestamp of the end revision until which the data was valid. Only used if the ValidityAuditStrategy is used, and org.hibernate.envers.audit_strategy_validity_store_revend_timestamp evaluates to true.

org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric(default: false )

Boolean flag that controls whether the revision end timestamp field is treated as a Long data type. Only used if the ValidityAuditStrategy is used, and org.hibernate.envers.audit_strategy_validity_store_revend_timestamp evaluates to true.

org.hibernate.envers.audit_strategy_validity_revend_timestamp_legacy_placement(default: true )

Boolean flag that controls whether the revision end timestamp field is propagated to the joined subclass audit tables. Only used if the ValidityAuditStrategy is used, and org.hibernate.envers.audit_strategy_validity_store_revend_timestamp evaluates to true.

When set to true, the legacy mapping behavior is used such that the revision end timestamp is only maintained in the root entity audit table. When set to false, the revision end timestamp is maintained in both the root entity and joined subclass audit tables; allowing the potential to apply database partitioning to the joined subclass tables just like the root entity audit tables.

org.hibernate.envers.use_revision_entity_with_native_id (default: true )

Boolean flag that determines the strategy of revision number generation. Default implementation of revision entity uses native identifier generator.

If the current database engine does not support identity columns, users are advised to set this property to false.

In this case revision numbers are created by preconfigured org.hibernate.id.enhanced.SequenceStyleGenerator. See: org.hibernate.envers.DefaultRevisionEntity and org.hibernate.envers.enhanced.SequenceIdRevisionEntity.

org.hibernate.envers.track_entities_changed_in_revision (default: false )

Should entity types, that have been modified during each revision, be tracked. The default implementation creates REVCHANGES table that stores entity names of modified persistent objects. Single record encapsulates the revision identifier (foreign key to REVINFO table) and a string value. For more information, refer to Tracking entity names modified during revisions and Querying for entity types modified in a given revision.

org.hibernate.envers.global_with_modified_flag (default: false, can be individually overridden with @Audited( withModifiedFlag = true ) )

Should property modification flags be stored for all audited entities and all properties.

When set to true, for all properties an additional boolean column in the audit tables will be created, filled with information if the given property changed in the given revision.

When set to false, such column can be added to selected entities or properties using the @Audited annotation.

org.hibernate.envers.modified_flag_suffix (default: _MOD )

The suffix for columns storing "Modified Flags".

For example, a property called "age", will by default get modified flag with column name "age_MOD".

org.hibernate.envers.modified_column_naming_strategy (default: org.hibernate.envers.boot.internal.LegacyModifiedColumnNamingStrategy )

The naming strategy to be used for modified flag columns in the audit metadata.

org.hibernate.envers.embeddable_set_ordinal_field_name (default: SETORDINAL )

Name of column used for storing ordinal of the change in sets of embeddable elements.

org.hibernate.envers.cascade_delete_revision (default: false )

While deleting revision entry, remove data of associated audited entities. Requires database support for cascade row removal.

org.hibernate.envers.allow_identifier_reuse (default: false )

Guarantees proper validity audit strategy behavior when application reuses identifiers of deleted entities. Exactly one row with null end date exists for each identifier.

org.hibernate.envers.original_id_prop_name (default: originalId )

Specifies the composite-id key property name used by the audit table mappings.

org.hibernate.envers.find_by_revision_exact_match (default: false )

Specifies whether or not AuditReader#find methods which accept a revision-number argument are to find results based on fuzzy-match or exact-match behavior.

The old (legacy) behavior has always been to perform a fuzzy-match where these methods would return a match if any revision existed for the primary-key with a revision-number less-than or equal-to the revision method argument. This behavior is great when you want to find the snapshot of a non-related entity based on another entity’s revision number.

The new (optional) behavior when this option is enabled forces the query to perform an exact-match instead. In order for these methods to return a non-null value, a revision entry must exist for the entity with the specified primary key and revision number; otherwise the result will be null.

org.hibernate.envers.global_relation_not_found_legacy_flag (default: true )

Globally defines whether legacy relation not-found behavior should be used or not.

By specifying true, any EntityNotFoundException errors will be thrown unless the Audited annotation explicitly specifies to ignore not-found relations. By specifying false, any EntityNotFoundException will be be ignored unless the Audited annotation explicitly specifies to raise the error rather than silently ignore not-found relations.

The following configuration options have been added recently and should be regarded as experimental:

  1. org.hibernate.envers.track_entities_changed_in_revision

  2. org.hibernate.envers.using_modified_flag

  3. org.hibernate.envers.modified_flag_suffix

  4. org.hibernate.envers.modified_column_naming_strategy

  5. org.hibernate.envers.original_id_prop_name

  6. org.hibernate.envers.find_by_revision_exact_match

  7. org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric

  8. org.hibernate.envers.global_relation_not_found_legacy_flag

24.3. Additional mapping annotations

The name of the audit table can be set on a per-entity basis, using the @AuditTable annotation. It may be tedious to add this annotation to every audited entity, so if possible, it’s better to use a prefix/suffix.

If you have a mapping with secondary tables, audit tables for them will be generated in the same way (by adding the prefix and suffix). If you wish to overwrite this behavior, you can use the @SecondaryAuditTable and @SecondaryAuditTables annotations.

If you have a mapping with collection tables, the audit table for them will be generated in the same way (by using the prefix and suffix). If you wish to overwrite this behavior, you can use the @CollectionAuditTable annotations.

If you’d like to override auditing behavior of some fields/properties inherited from @MappedSuperclass or in an embedded component, you can apply the @AuditOverride annotation on the subtype or usage site of the component.

If you want to audit a relation mapped with @OneToMany and @JoinColumn, please see Mapping exceptions for a description of the additional @AuditJoinTable annotation that you’ll probably want to use.

If you want to audit a relation, where the target entity is not audited (that is the case for example with dictionary-like entities, which don’t change and don’t have to be audited), just annotate it with @Audited( targetAuditMode = RelationTargetAuditMode.NOT_AUDITED ). Then, while reading historic versions of your entity, the relation will always point to the "current" related entity. By default Envers throws jakarta.persistence.EntityNotFoundException when "current" entity does not exist in the database. Apply @NotFound( action = NotFoundAction.IGNORE ) annotation to silence the exception and assign null value instead. The hereby solution causes implicit eager loading of to-one relations.

If you’d like to audit properties of a superclass of an entity, which are not explicitly audited (they don’t have the @Audited annotation on any properties or on the class), you can set the @AuditOverride( forClass = SomeEntity.class, isAudited = true/false ) annotation.

The @Audited annotation also features an auditParents attribute but it’s now deprecated in favor of @AuditOverride.

24.4. Choosing an audit strategy

After the basic configuration, it is important to choose the audit strategy that will be used to persist and retrieve audit information. There is a trade-off between the performance of persisting and the performance of querying the audit information. Currently, there are two audit strategies.

  1. The default audit strategy persists the audit data together with a start revision. For each row inserted, updated or deleted in an audited table, one or more rows are inserted in the audit tables, together with the start revision of its validity. Rows in the audit tables are never updated after insertion. Queries of audit information use subqueries to select the applicable rows in the audit tables.

    These subqueries are notoriously slow and difficult to index.
  2. The alternative is a validity audit strategy. This strategy stores the start-revision and the end-revision of audit information. For each row inserted, updated or deleted in an audited table, one or more rows are inserted in the audit tables, together with the start revision of its validity. But at the same time, the end-revision field of the previous audit rows (if available) is set to this revision. Queries on the audit information can then use 'between start and end revision' instead of subqueries as used by the default audit strategy.

    The consequence of this strategy is that persisting audit information will be a bit slower because of the extra updates involved, but retrieving audit information will be a lot faster.

    This can be improved even further by adding extra indexes.

24.4.1. Configuring the ValidityAuditStrategy

To better visualize how the ValidityAuditStrategy works, consider the following exercise where we replay the previous audit logging example for the Customer entity.

First, you need to configure the ValidityAuditStrategy:

Example 655. Configuring the ValidityAuditStrategy
options.put(
	EnversSettings.AUDIT_STRATEGY,
	ValidityAuditStrategy.class.getName()
);

If, you’re using the persistence.xml configuration file, then the mapping will look as follows:

<property
    name="org.hibernate.envers.audit_strategy"
    value="org.hibernate.envers.strategy.ValidityAuditStrategy"
/>

Once you configured the ValidityAuditStrategy, the following schema is going to be automatically generated:

Example 656. Envers schema for the ValidityAuditStrategy
create table Customer (
    id bigint not null,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    primary key (id)
)

create table Customer_AUD (
   id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    REVEND integer,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    primary key (id, REV)
)

create table REVINFO (
    REV integer generated by default as identity,
    REVTSTMP bigint,
    primary key (REV)
)

alter table Customer_AUD
    add constraint FK5ecvi1a0ykunrriib7j28vpdj
    foreign key (REV)
    references REVINFO

alter table Customer_AUD
    add constraint FKqd4fy7ww1yy95wi4wtaonre3f
    foreign key (REVEND)
    references REVINFO

As you can see, the REVEND column is added as well as its foreign key to the REVINFO table.

When rerunning the previous Customer audit log queries against the ValidityAuditStrategy, we get the following results:

Example 657. Getting the first revision for the Customer entity
select
    c.id as id1_1_,
    c.REV as REV2_1_,
    c.REVTYPE as REVTYPE3_1_,
    c.REVEND as REVEND4_1_,
    c.created_on as created_5_1_,
    c.firstName as firstNam6_1_,
    c.lastName as lastName7_1_
from
    Customer_AUD c
where
    c.REV <= ?
    and c.REVTYPE <> ?
    and (
        c.REVEND > ?
        or c.REVEND is null
    )

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]

Compared to the default strategy, the ValidityAuditStrategy generates simpler queries that can render better SQL execution plans.

24.5. Revision Log

When Envers starts a new revision, it creates a new revision entity which stores information about the revision.

By default, that includes just:

revision number

An integral value (int/Integer or long/Long). Essentially, the primary key of the revision.

A revision number value should always be increasing and never overflows.

The default implementations provided by Envers use an int data type which has an upper bounds of Integer.MAX_VALUE. It is critical that users consider whether this upper bounds is feasible for your application. If a large range is needed, consider using a custom revision entity mapping using a long data type.

In the event that the revision number reaches its upper bounds wrapping around becoming negative, an AuditException will be thrown causing the current transaction to be rolled back. This guarantees that the audit history remains in a valid state that can be queried by the Envers Query API.

revision timestamp

Either a long/Long or java.util.Date value representing the instant at which the revision was made. When using a java.util.Date, instead of a long/Long for the revision timestamp, take care not to store it to a column data type which will lose precision.

Envers handles this information as an entity. By default it uses its own internal class to act as the entity, mapped to the REVINFO table. You can, however, supply your own approach to collecting this information which might be useful to capture additional details such as who made a change or the IP address from which the request came. There are two things you need to make this work:

  1. First, you will need to tell Envers about the entity you wish to use. Your entity must use the @org.hibernate.envers.RevisionEntity annotation. It must define the two attributes described above annotated with @org.hibernate.envers.RevisionNumber and @org.hibernate.envers.RevisionTimestamp, respectively. You can extend from org.hibernate.envers.DefaultRevisionEntity, if you wish, to inherit all these required behaviors.

    Simply add the custom revision entity as you do your normal entities and Envers will find it.

    It is an error for there to be multiple entities marked as @org.hibernate.envers.RevisionEntity.
  2. Second, you need to tell Envers how to create instances of your revision entity which is handled by the newRevision( Object revisionEntity ) method of the org.hibernate.envers.RevisionListener interface.

    You tell Envers your custom org.hibernate.envers.RevisionListener implementation to use by specifying it on the @org.hibernate.envers.RevisionEntity annotation, using the value attribute. If your RevisionListener class is inaccessible from @RevisionEntity (e.g. it exists in a different module), set org.hibernate.envers.revision_listener property to its fully qualified class name. Class name defined by the configuration parameter overrides the revision entity’s value attribute.

Considering we have a CurrentUser utility which stores the currently logged user:

Example 658. CurrentUser utility
public static class CurrentUser {

	public static final CurrentUser INSTANCE = new CurrentUser();

	private static final ThreadLocal<String> storage = new ThreadLocal<>();

	public void logIn(String user) {
		storage.set(user);
	}

	public void logOut() {
		storage.remove();
	}

	public String get() {
		return storage.get();
	}
}

Now, we need to provide a custom @RevisionEntity to store the currently logged user

Example 659. Custom @RevisionEntity example
@Entity(name = "CustomRevisionEntity")
@Table(name = "CUSTOM_REV_INFO")
@RevisionEntity(CustomRevisionEntityListener.class)
public static class CustomRevisionEntity extends DefaultRevisionEntity {

	private String username;

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}
}

With the custom RevisionEntity implementation in place, we only need to provide the RevisionEntity implementation which acts as a factory of RevisionEntity instances.

Example 660. Custom @RevisionListener example
public static class CustomRevisionEntityListener implements RevisionListener {

	public void newRevision(Object revisionEntity) {
		CustomRevisionEntity customRevisionEntity =
			(CustomRevisionEntity) revisionEntity;

		customRevisionEntity.setUsername(
			CurrentUser.INSTANCE.get()
		);
	}
}

When generating the database schema, Envers creates the following RevisionEntity table:

Example 661. Auto-generated RevisionEntity Envers table
create table CUSTOM_REV_INFO (
    id integer not null,
    timestamp bigint not null,
    username varchar(255),
    primary key (id)
)

You can see the username column in place.

Now, when inserting a Customer entity, Envers generates the following statements:

Example 662. Auditing using the custom @RevisionEntity instance
CurrentUser.INSTANCE.logIn("Vlad Mihalcea");

scope.inTransaction( entityManager -> {
	Customer customer = new Customer();
	customer.setId(1L);
	customer.setFirstName("John");
	customer.setLastName("Doe");

	entityManager.persist(customer);
});

CurrentUser.INSTANCE.logOut();
insert
into
    Customer
    (created_on, firstName, lastName, id)
values
    (?, ?, ?, ?)

-- binding parameter [1] as [TIMESTAMP] - [Thu Jul 27 15:45:00 EEST 2017]
-- binding parameter [2] as [VARCHAR]   - [John]
-- binding parameter [3] as [VARCHAR]   - [Doe]
-- binding parameter [4] as [BIGINT]    - [1]

insert
into
    CUSTOM_REV_INFO
    (timestamp, username, id)
values
    (?, ?, ?)

-- binding parameter [1] as [BIGINT]  - [1501159500888]
-- binding parameter [2] as [VARCHAR] - [Vlad Mihalcea]
-- binding parameter [3] as [INTEGER] - [1]

insert
into
    Customer_AUD
    (REVTYPE, created_on, firstName, lastName, id, REV)
values
    (?, ?, ?, ?, ?, ?)

-- binding parameter [1] as [INTEGER]   - [0]
-- binding parameter [2] as [TIMESTAMP] - [Thu Jul 27 15:45:00 EEST 2017]
-- binding parameter [3] as [VARCHAR]   - [John]
-- binding parameter [4] as [VARCHAR]   - [Doe]
-- binding parameter [5] as [BIGINT]    - [1]
-- binding parameter [6] as [INTEGER]   - [1]

As demonstrated by the example above, the username is properly set and propagated to the CUSTOM_REV_INFO table.

This strategy is deprecated since version 5.2. The alternative is to use dependency injection offered as of version 5.3.

An alternative method to using the org.hibernate.envers.RevisionListener is to instead call the getCurrentRevision( Class<T> revisionEntityClass, boolean persist ) method of the org.hibernate.envers.AuditReader interface to obtain the current revision, and fill it with desired information.

The method accepts a persist parameter indicating whether the revision entity should be persisted prior to returning from this method:

true

ensures that the returned entity has access to its identifier value (revision number), but the revision entity will be persisted regardless of whether there are any audited entities changed.

false

means that the revision number will be null, but the revision entity will be persisted only if some audited entities have changed.

As of Hibernate Envers 5.3, dependency injection is now supported for a RevisionListener.

This feature is up to the various dependency frameworks, such as CDI and Spring, to supply the necessary implementation during Hibernate ORM bootstrap to support injection. If no qualifying implementation is supplied, the RevisionListener will be constructed without injection.

24.6. Tracking entity names modified during revisions

By default, entity types that have been changed in each revision are not being tracked. This implies the necessity to query all tables storing audited data in order to retrieve changes made during the specified revision. Envers provides a simple mechanism that creates REVCHANGES table which stores entity names of modified persistent objects. Single record encapsulates the revision identifier (foreign key to REVINFO table) and a string value.

Tracking of modified entity names can be enabled in three different ways:

  1. Set org.hibernate.envers.track_entities_changed_in_revision parameter to true. In this case org.hibernate.envers.DefaultTrackingModifiedEntitiesRevisionEntity will be implicitly used as the revision log entity.

  2. Create a custom revision entity that extends org.hibernate.envers.DefaultTrackingModifiedEntitiesRevisionEntity class.

    @Entity(name = "CustomTrackingRevisionEntity")
    @Table(name = "TRACKING_REV_INFO")
    @RevisionEntity
    public static class CustomTrackingRevisionEntity
    	extends DefaultTrackingModifiedEntitiesRevisionEntity {
    
    }
  3. Mark an appropriate field of a custom revision entity with @org.hibernate.envers.ModifiedEntityNames annotation. The property is required to be of Set<String> type.

    @Entity(name = "CustomTrackingRevisionEntity")
    @Table(name = "TRACKING_REV_INFO")
    @RevisionEntity
    public static class CustomTrackingRevisionEntity extends DefaultRevisionEntity {
    
        @ElementCollection
        @JoinTable(
            name = "REVCHANGES",
            joinColumns = @JoinColumn(name = "REV")
       )
        @Column(name = "ENTITYNAME")
        @ModifiedEntityNames
        private Set<String> modifiedEntityNames = new HashSet<>();
    
        public Set<String> getModifiedEntityNames() {
            return modifiedEntityNames;
        }
    }

Considering we have a Customer entity illustrated by the following example:

Example 663. Customer entity before renaming
@Audited
@Entity(name = "Customer")
public static class Customer {

    @Id
    private Long id;

    private String firstName;

    private String lastName;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "created_on")
    @CreationTimestamp
    private Date createdOn;

    //Getters and setters are omitted for brevity
}

If the Customer entity class name is changed to ApplicationCustomer, Envers is going to insert a new record in the REVCHANGES table with the previous entity class name:

Example 664. Customer entity after renaming
@Audited
@Entity(name = "Customer")
public static class ApplicationCustomer {

    @Id
    private Long id;

    private String firstName;

    private String lastName;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "created_on")
    @CreationTimestamp
    private Date createdOn;

    //Getters and setters are omitted for brevity
}
insert
into
    REVCHANGES
    (REV, ENTITYNAME)
values
    (?, ?)

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [VARCHAR] - [org.hibernate.userguide.envers.EntityTypeChangeAuditTest$Customer]

Users, that have chosen one of the approaches listed above, can retrieve all entities modified in a specified revision by utilizing API described in Querying for entity types modified in a given revision.

Users are also allowed to implement custom mechanisms of tracking modified entity types. In this case, they shall pass their own implementation of org.hibernate.envers.EntityTrackingRevisionListener interface as the value of @org.hibernate.envers.RevisionEntity annotation.

EntityTrackingRevisionListener interface exposes one method that notifies whenever audited entity instance has been added, modified or removed within current revision boundaries.

Example 665. The EntityTrackingRevisionListener implementation
public static class CustomTrackingRevisionListener implements EntityTrackingRevisionListener {

	@Override
	public void entityChanged(Class entityClass,
							  String entityName,
							  Object entityId,
							  RevisionType revisionType,
							  Object revisionEntity) {
		String type = entityClass.getName();
		((CustomTrackingRevisionEntity) revisionEntity).addModifiedEntityType(type);
	}

	@Override
	public void newRevision(Object revisionEntity) {
	}
}

The CustomTrackingRevisionListener adds the fully-qualified class name to the modifiedEntityTypes attribute of the CustomTrackingRevisionEntity.

Example 666. The RevisionEntity using the custom EntityTrackingRevisionListener
@Entity(name = "CustomTrackingRevisionEntity")
@Table(name = "TRACKING_REV_INFO")
@RevisionEntity(CustomTrackingRevisionListener.class)
public static class CustomTrackingRevisionEntity {

	@Id
	@GeneratedValue
	@RevisionNumber
	private int customId;

	@RevisionTimestamp
	private long customTimestamp;

	@OneToMany(
		mappedBy="revision",
		cascade={
			CascadeType.PERSIST,
			CascadeType.REMOVE
		}
	)
	private Set<EntityType> modifiedEntityTypes = new HashSet<>();

	public Set<EntityType> getModifiedEntityTypes() {
		return modifiedEntityTypes;
	}

	public void addModifiedEntityType(String entityClassName) {
		modifiedEntityTypes.add(new EntityType(this, entityClassName));
	}
}

The CustomTrackingRevisionEntity contains a @OneToMany list of ModifiedTypeRevisionEntity

Example 667. The EntityType encapsulates the entity type name before a class name modification
@Entity(name = "EntityType")
public static class EntityType {

	@Id
	@GeneratedValue
	private Integer id;

	@ManyToOne
	private CustomTrackingRevisionEntity revision;

	private String entityClassName;

	private EntityType() {
	}

	public EntityType(CustomTrackingRevisionEntity revision, String entityClassName) {
		this.revision = revision;
		this.entityClassName = entityClassName;
	}

	//Getters and setters are omitted for brevity
}

Now, when fetching the CustomTrackingRevisionEntity, you can get access to the previous entity class name.

Example 668. Getting the EntityType through the CustomTrackingRevisionEntity
AuditReader auditReader = AuditReaderFactory.get(entityManager);

List<Number> revisions = auditReader.getRevisions(
	ApplicationCustomer.class,
	1L
);

CustomTrackingRevisionEntity revEntity = auditReader.findRevision(
	CustomTrackingRevisionEntity.class,
	revisions.get(0)
);

Set<EntityType> modifiedEntityTypes = revEntity.getModifiedEntityTypes();
assertEquals(1, modifiedEntityTypes.size());

EntityType entityType = modifiedEntityTypes.iterator().next();
assertEquals(
	Customer.class.getName(),
	entityType.getEntityClassName()
);

24.7. Tracking entity changes at the property level

By default, the only information stored by Envers are revisions of modified entities. This approach lets users create audit queries based on historical values of entity properties. Sometimes it is useful to store additional metadata for each revision, when you are interested also in the type of changes, not only about the resulting values.

The feature described in Tracking entity names modified during revisions makes it possible to tell which entities were modified in a given revision.

The feature described here takes it one step further. Modification Flags enable Envers to track which properties of audited entities were modified in a given revision.

Tracking entity changes at the property level can be enabled by:

  1. setting org.hibernate.envers.global_with_modified_flag configuration property to true. This global switch will cause adding modification flags to be stored for all audited properties of all audited entities.

  2. using @Audited( withModifiedFlag = true ) on a property or on an entity.

The trade-off coming with this functionality is an increased size of audit tables and a very little, almost negligible, performance drop during audit writes. This is due to the fact that every tracked property has to have an accompanying boolean column in the schema that stores information about the property modifications. Of course, it is Enver’s job to fill these columns accordingly - no additional work by the developer is required. Because of costs mentioned, it is recommended to enable the feature selectively, when needed with use of the granular configuration means described above.

Example 669. Mapping for tracking entity changes at the property level
@Audited(withModifiedFlag = true)
@Entity(name = "Customer")
public static class Customer {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	@Temporal(TemporalType.TIMESTAMP)
	@Column(name = "created_on")
	@CreationTimestamp
	private Date createdOn;

	//Getters and setters are omitted for brevity
}
create table Customer_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    created_on timestamp,
    createdOn_MOD boolean,
    firstName varchar(255),
    firstName_MOD boolean,
    lastName varchar(255),
    lastName_MOD boolean,
    primary key (id, REV)
)

As you can see, every property features a _MOD column (e.g. createdOn_MOD) in the audit log.

Example 670. Tracking entity changes at the property level example
Customer customer = entityManager.find(Customer.class, 1L);
customer.setLastName("Doe Jr.");
update
    Customer
set
    created_on = ?,
    firstName = ?,
    lastName = ?
where
    id = ?

-- binding parameter [1] as [TIMESTAMP] - [2017-07-31 15:58:20.342]
-- binding parameter [2] as [VARCHAR]   - [John]
-- binding parameter [3] as [VARCHAR]   - [Doe Jr.]
-- binding parameter [4] as [BIGINT]    - [1]

insert
into
    REVINFO
    (REV, REVTSTMP)
values
    (null, ?)

-- binding parameter [1] as [BIGINT] - [1501505900439]

insert
into
    Customer_AUD
    (REVTYPE, created_on, createdOn_MOD, firstName, firstName_MOD, lastName, lastName_MOD, id, REV)
values
    (?, ?, ?, ?, ?, ?, ?, ?, ?)

-- binding parameter [1] as [INTEGER]   - [1]
-- binding parameter [2] as [TIMESTAMP] - [2017-07-31 15:58:20.342]
-- binding parameter [3] as [BOOLEAN]   - [false]
-- binding parameter [4] as [VARCHAR]   - [John]
-- binding parameter [5] as [BOOLEAN]   - [false]
-- binding parameter [6] as [VARCHAR]   - [Doe Jr.]
-- binding parameter [7] as [BOOLEAN]   - [true]
-- binding parameter [8] as [BIGINT]    - [1]
-- binding parameter [9] as [INTEGER]   - [2]

To see how "Modified Flags" can be utilized, check out the very simple query API that uses them: Querying for entity revisions that modified a given property.

24.8. Selecting strategy for tracking property level changes

By default, Envers uses the legacy modified column naming strategy. This strategy is designed to add columns based on the following rule-set:

  1. If property is annotated with @Audited and the modifiedColumnName attribute is specified, the column will directly be based on the supplied name.

  2. If property is not annotated with @Audited or if no modifiedColumnName attribute is given, the column will be named after the java class property, appended with the configured suffix, the default being _MOD.

While this strategy has no performance drawbacks, it does present concerns for users who prefer consistency without verbosity. Lets take the following entity mapping as an example.

@Audited(withModifiedFlags = true)
@Entity
public class Customer {
  @Id
  private Integer id;
  @Column(name = "customer_name")
  private String name;
}

This mapping will actually lead to some inconsistent naming between columns, see below for how the model’s name will be stored in customer_name but the modified column that tracks whether this column changes between revisions is named name_MOD.

CREATE TABLE Customer_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint not null,
    customer_name varchar(255),
    name_MOD boolean,
    primary key(id, REV)
)

An additional strategy called improved, aims to address these inconsistent column naming concerns. This strategy uses the following rule-set:

  1. Property is a Basic type (Single Column valued property)

    1. Use the modifiedColumnName directly if one is supplied on the property mapping

    2. Otherwise use the resolved ORM column name appended with the modified flag suffix configured value

  2. Property is an Association (to-one mapping) with a Foreign Key using a single column

    1. Use the modifiedColumnName directly if one is supplied on the property mapping

    2. Otherwise use the resolved ORM column name appended with the modified flag suffix configured value

  3. Property is an Association (to-one mapping) with a Foreign Key using multiple columns

    1. Use the modifiedColumnName directly if one is supplied on the property mapping

    2. Otherwise use the property name appended with the modified flag suffix configured value

  4. Property is an Embeddable

    1. Use the modifiedColumnName directly if one is supplied on the property mapping

    2. Otherwise use the property name appended with the modified flag suffix configured value

While using this strategy, the same Customer mapping will generate the following table schema:

CREATE TABLE Customer_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint not null,
    customer_name varchar(255),
    customer_name_MOD boolean,
    primary key(id, REV)
)

When already using Envers in conjunction with the modified columns flag feature, it is advised not to enable the new strategy immediately as schema changes would be required. You will need to either migrate your existing schema manually to adhere to the rules above or use the explicit modifiedColumnName attribute on the @Audited annotation for existing columns that use the feature.

To configure a custom strategy implementation or use the improved strategy, the configuration option org.hibernate.envers.modified_column_naming_strategy will need to be set. This option can be the fully qualified class name of a ModifiedColumnNameStrategy implementation or legacy or improved for either of the two provided implementations.

24.9. Queries

You can think of historic data as having two dimensions:

horizontal

The state of the database at a given revision. Thus, you can query for entities as they were at revision N.

vertical

The revisions, at which entities changed. Hence, you can query for revisions, in which a given entity changed.

The queries in Envers are similar to Hibernate Criteria queries, so if you are familiar with them, using Envers queries will be much easier.

The main limitation of the current queries implementation is that you cannot traverse relations. You can only specify constraints on the ids of the related entities, and only on the "owning" side of the relation. This, however, will be changed in future releases.

The queries on the audited data will be in many cases much slower than corresponding queries on "live" data, as, especially for the default audit strategy, they involve correlated subselects.

Queries are improved both in terms of speed and possibilities when using the validity audit strategy, which stores both start and end revisions for entities. See Configuring the ValidityAuditStrategy for a more detailed discussion.

24.10. Querying for entities of a class at a given revision

The entry point for this type of queries is:

Example 671. Getting the Customer entity at a given revision
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(0))
.getSingleResult();

assertEquals("Doe", customer.getLastName());

24.11. Querying for entities using filtering criteria

You can then specify constraints, which should be met by the entities returned, by adding restrictions, which can be obtained using the AuditEntity factory class.

For example, to select only entities where the firstName property is equal to "John":

Example 672. Getting the Customer audit log with a given firstName attribute value
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.property("firstName").eq("John"))
.getResultList();

assertEquals(2, customers.size());
assertEquals("Doe", customers.get(0).getLastName());
assertEquals("Doe Jr.", customers.get(1).getLastName());

And, to select only entities whose relationships are related to a given entity, you can use either the target entity or its identifier.

Example 673. Getting the Customer entities whose address attribute matches the given entity reference
Address address = entityManager.getReference(Address.class, 1L);

List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.property("address").eq(address))
.getResultList();

assertEquals(2, customers.size());
select
    c.id as id1_3_,
    c.REV as REV2_3_,
    c.REVTYPE as REVTYPE3_3_,
    c.REVEND as REVEND4_3_,
    c.created_on as created_5_3_,
    c.firstName as firstNam6_3_,
    c.lastName as lastName7_3_,
    c.address_id as address_8_3_
from
    Customer_AUD c
where
    c.address_id = ?
order by
    c.REV asc

-- binding parameter [1] as [BIGINT] - [1]

The same SQL is generated even if we provide the identifier instead of the target entity reference.

Example 674. Getting the Customer entities whose address identifier matches the given entity identifier
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.relatedId("address").eq(1L))
.getResultList();

assertEquals(2, customers.size());

Apart from strict equality matching, you can also use an IN clause to provide multiple entity identifiers:

Example 675. Getting the Customer entities whose address identifier matches one of the given entity identifiers
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.add(AuditEntity.relatedId("address").in(new Object[] { 1L, 2L }))
.getResultList();

assertEquals(2, customers.size());
select
    c.id as id1_3_,
    c.REV as REV2_3_,
    c.REVTYPE as REVTYPE3_3_,
    c.REVEND as REVEND4_3_,
    c.created_on as created_5_3_,
    c.firstName as firstNam6_3_,
    c.lastName as lastName7_3_,
    c.address_id as address_8_3_
from
    Customer_AUD c
where
    c.address_id in (
        ? , ?
    )
order by
    c.REV asc

-- binding parameter [1] as [BIGINT] - [1]
-- binding parameter [2] as [BIGINT] - [2]

You can limit the number of results, order them, and set aggregations and projections (except grouping) in the usual way. When your query is complete, you can obtain the results by calling the getSingleResult() or getResultList() methods.

A full query, can look for example like this:

Example 676. Getting the Customer entities using filtering and pagination
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, true, true)
.addOrder(AuditEntity.property("lastName").desc())
.add(AuditEntity.relatedId("address").eq(1L))
.setFirstResult(1)
.setMaxResults(2)
.getResultList();

assertEquals(1, customers.size());
select
    c.id as id1_3_,
    c.REV as REV2_3_,
    c.REVTYPE as REVTYPE3_3_,
    c.REVEND as REVEND4_3_,
    c.created_on as created_5_3_,
    c.firstName as firstNam6_3_,
    c.lastName as lastName7_3_,
    c.address_id as address_8_3_
from
    Customer_AUD c
where
    c.address_id = ?
order by
    c.lastName desc
limit ?
offset ?

24.12. Querying for revisions, at which entities of a given class changed

The entry point for this type of queries is:

AuditQuery query = AuditReaderFactory.get(entityManager)
	.createQuery()
	.forRevisionsOfEntity(Customer.class, false, true);

You can add constraints to this query in the same way as to the previous one.

There are some additional possibilities:

  1. using AuditEntity.revisionNumber() you can specify constraints, projections and order on the revision number, in which the audited entity was modified.

  2. similarly, using AuditEntity.revisionProperty( propertyName ) you can specify constraints, projections and order on a property of the revision entity, corresponding to the revision in which the audited entity was modified.

  3. AuditEntity.revisionType() gives you access as above to the type of the revision (ADD, MOD, DEL).

Using these methods, you can order the query results by revision number, set projection or constraint the revision number to be greater or less than a specified value, etc. For example, the following query will select the smallest revision number, at which entity of class MyEntity with id entityId has changed, after revision number 2:

Number revision = (Number) AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.addProjection(AuditEntity.revisionNumber().min())
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.revisionNumber().gt(2))
.getSingleResult();

The second additional feature you can use in queries for revisions is the ability to maximize/minimize a property.

For example, if you want to select the smallest possible revision at which the value of the createdOn attribute was larger then a given value, you can run the following query:

Number revision = (Number) AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.addProjection(AuditEntity.revisionNumber().min())
.add(AuditEntity.id().eq(1L))
.add(
	AuditEntity.property("createdOn")
	.minimize()
	.add(AuditEntity.property("createdOn")
		.ge(
			Timestamp.from(
				LocalDateTime.now()
					.minusDays(1)
					.toInstant(ZoneOffset.UTC)
				)
		)
	)
)
.getSingleResult();

The minimize() and maximize() methods return a criterion, to which you can add constraints, which must be met by the entities with the maximized/minimized properties.

You probably also noticed that there are two boolean parameters, passed when creating the query.

selectEntitiesOnly

The first parameter is only valid when you don’t set an explicit projection.

If true, the result of the query will be a list of entities (which changed at revisions satisfying the specified constraints).

If false, the result will be a list of three element arrays:

  • the first element will be the changed entity instance.

  • the second will be an entity containing revision data (if no custom entity is used, this will be an instance of DefaultRevisionEntity).

  • the third will be the type of the revision (one of the values of the RevisionType enumeration: ADD, MOD, DEL).

selectDeletedEntities

The second parameter specifies if revisions, in which the entity was deleted should be included in the results.

If yes, such entities will have the revision type DEL and all attributes, except the id, will be set to null.

Another useful feature is AggregatedAuditExpression#computeAggregationInInstanceContext(). This can be used to create an aggregate query based on the entity instance primary key.

For example, if you wanted to locate all customers but only wanted to retrieve the instances with the maximum revision number, you would use the following query:

List<Customer> results = AuditReaderFactory
	.get(entityManager)
	.createQuery()
	.forRevisionsOfEntity(Customer.class, true, false)
	.add(AuditEntity.revisionNumber().maximize().computeAggregationInInstanceContext())
	.getResultList();

In other words, the result set would contain a list of Customer instances, one per primary key. Each instance would hold the audited property data at the maximum revision number for each Customer primary key.

24.13. Querying for entity revisions that modified a given property

For the two types of queries described above it’s possible to use special Audit criteria called hasChanged() and hasNotChanged() that make use of the functionality described in Tracking entity changes at the property level.

Let’s have a look at various queries that can benefit from these two criteria.

First, you must make sure that your entity can track modification flags:

Example 677. Valid only when audit logging tracks entity attribute modification flags
@Audited(withModifiedFlag = true)

The following query will return all revisions of the Customer entity with the given id, for which the lastName property has changed.

Example 678. Getting all Customer revisions for which the lastName attribute has changed
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.getResultList();
select
    c.id as id1_3_0_,
    c.REV as REV2_3_0_,
    defaultrev1_.REV as REV1_4_1_,
    c.REVTYPE as REVTYPE3_3_0_,
    c.REVEND as REVEND4_3_0_,
    c.created_on as created_5_3_0_,
    c.createdOn_MOD as createdO6_3_0_,
    c.firstName as firstNam7_3_0_,
    c.firstName_MOD as firstNam8_3_0_,
    c.lastName as lastName9_3_0_,
    c.lastName_MOD as lastNam10_3_0_,
    c.address_id as address11_3_0_,
    c.address_MOD as address12_3_0_,
    defaultrev1_.REVTSTMP as REVTSTMP2_4_1_
from
    Customer_AUD c cross
join
    REVINFO defaultrev1_
where
    c.id = ?
    and c.lastName_MOD = ?
    and c.REV=defaultrev1_.REV
order by
    c.REV asc

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [BOOLEAN] - [true]

Using this query we won’t get all other revisions in which lastName wasn’t touched. From the SQL query you can see that the lastName_MOD column is being used in the WHERE clause, hence the aforementioned requirement for tracking modification flags.

Of course, nothing prevents users from combining hasChanged condition with some additional criteria.

Example 679. Getting all Customer revisions for which the lastName attribute has changed and the firstName attribute has not changed
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forRevisionsOfEntity(Customer.class, false, true)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.add(AuditEntity.property("firstName").hasNotChanged())
.getResultList();
select
    c.id as id1_3_0_,
    c.REV as REV2_3_0_,
    defaultrev1_.REV as REV1_4_1_,
    c.REVTYPE as REVTYPE3_3_0_,
    c.REVEND as REVEND4_3_0_,
    c.created_on as created_5_3_0_,
    c.createdOn_MOD as createdO6_3_0_,
    c.firstName as firstNam7_3_0_,
    c.firstName_MOD as firstNam8_3_0_,
    c.lastName as lastName9_3_0_,
    c.lastName_MOD as lastNam10_3_0_,
    c.address_id as address11_3_0_,
    c.address_MOD as address12_3_0_,
    defaultrev1_.REVTSTMP as REVTSTMP2_4_1_
from
    Customer_AUD c cross
join
    REVINFO defaultrev1_
where
    c.id=?
    and c.lastName_MOD=?
    and c.firstName_MOD=?
    and c.REV=defaultrev1_.REV
order by
    c.REV asc

-- binding parameter [1] as [BIGINT]  - [1]
-- binding parameter [2] as [BOOLEAN] - [true]
-- binding parameter [3] as [BOOLEAN] - [false]

To get the Customer entities changed at a given revisionNumber with lastName modified and firstName untouched, we have to use the forEntitiesModifiedAtRevision query:

Example 680. Getting the Customer entity for a given revision if the lastName attribute has changed and the firstName attribute has not changed
Customer customer = (Customer) AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesModifiedAtRevision(Customer.class, 2)
.add(AuditEntity.id().eq(1L))
.add(AuditEntity.property("lastName").hasChanged())
.add(AuditEntity.property("firstName").hasNotChanged())
.getSingleResult();
select
    c.id as id1_3_,
    c.REV as REV2_3_,
    c.REVTYPE as REVTYPE3_3_,
    c.REVEND as REVEND4_3_,
    c.created_on as created_5_3_,
    c.createdOn_MOD as createdO6_3_,
    c.firstName as firstNam7_3_,
    c.firstName_MOD as firstNam8_3_,
    c.lastName as lastName9_3_,
    c.lastName_MOD as lastNam10_3_,
    c.address_id as address11_3_,
    c.address_MOD as address12_3_
from
    Customer_AUD c
where
    c.REV=?
    and c.id=?
    and c.lastName_MOD=?
    and c.firstName_MOD=?

-- binding parameter [1] as [INTEGER] - [2]
-- binding parameter [2] as [BIGINT]  - [1]
-- binding parameter [3] as [BOOLEAN] - [true]
-- binding parameter [4] as [BOOLEAN] - [false]

24.14. Querying for revisions of entity including property names that were modified

This feature described here is still considered experimental. It is subject to change in future releases based on user feedback to improve its usefulness.

Sometimes it may be useful to query entity revisions and also determine all the properties of that revision which were modified without having to issue multiple queries using hasChanged() and hasNotChanged() criteria.

You can now obtain this information easily by using the following query:

Example 681. Querying entity revisions including property names modified.
List results  = AuditReaderFactory.get( entityManager )
    .createQuery()
    .forRevisionsOfEntityWithChanges( Customer.class, false )
    .add( AuditEntity.id().eq( 1L ) )
    .getResultList();

for ( Object entry : results ) {
    final Object[] array = (Object[]) entry;
    final Set<String> propertiesChanged = (Set<String>) array[3];
    for ( String propertyName : propertiesChanged ) {
    /* Do something useful with the modified property `propertyName` */
    }
}

24.15. Querying for entity types modified in a given revision

The methods described below can be used only when the default mechanism of tracking changed entity types is enabled (see Tracking entity names modified during revisions).

This basic query allows retrieving entity names and corresponding Java classes changed in a specified revision:

Example 682. Retrieving entity names and corresponding Java classes changed in a specified revision
assertEquals(
    "org.hibernate.orm.test.envers.EntityTypeChangeAuditTest$Customer",
    AuditReaderFactory
        .get(entityManager)
        .getCrossTypeRevisionChangesReader()
        .findEntityTypes(1)
        .iterator().next()
        .getFirst()
   );
 assertEquals(
     "org.hibernate.orm.test.envers.EntityTypeChangeAuditTest$ApplicationCustomer",
     AuditReaderFactory
     .get(entityManager)
     .getCrossTypeRevisionChangesReader()
     .findEntityTypes(2)
     .iterator().next()
     .getFirst()
);

Other queries (also accessible from org.hibernate.envers.CrossTypeRevisionChangesReader):

List<Object> findEntities(Number)

Returns snapshots of all audited entities changed (added, updated and removed) in a given revision. Executes N + 1 SQL queries, where N is a number of different entity classes modified within specified revision.

List<Object> findEntities(Number, RevisionType)

Returns snapshots of all audited entities changed (added, updated or removed) in a given revision filtered by modification type. Executes N + 1 SQL queries, where N is a number of different entity classes modified within specified revision.

Map<RevisionType, List<Object>> findEntitiesGroupByRevisionType(Number)

Returns a map containing lists of entity snapshots grouped by modification operation (e.g. addition, update and removal). Executes 3N + 1 SQL queries, where N is a number of different entity classes modified within specified revision.

24.16. Querying for entities using entity relation joins

Relation join queries are considered experimental and may change in future releases.

Audit queries support the ability to apply constraints, projections, and sort operations based on entity relations. In order to traverse entity relations through an audit query, you must use the relation traversal API with a join type.

Relation joins can be applied to many-to-one and one-to-one mappings only when using JoinType.LEFT or JoinType.INNER.

The basis for creating an entity relation join query is as follows:

Example 683. INNER JOIN entity audit query
AuditQuery innerJoinAuditQuery = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER);
Example 684. LEFT JOIN entity audit query
AuditQuery innerJoinAuditQuery = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.LEFT);

Like any other query, constraints may be added to restrict the results.

For example, to find all Customer entities at a given revision whose addresses are in România, you can use the following query:

Example 685. Filtering the join relation with a WHERE clause predicate
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER)
.add(AuditEntity.property("country").eq("România"))
.getResultList();
select
    c.id as id1_3_,
    c.REV as REV2_3_,
    c.REVTYPE as REVTYPE3_3_,
    c.REVEND as REVEND4_3_,
    c.created_on as created_5_3_,
    c.firstName as firstNam6_3_,
    c.lastName as lastName7_3_,
    c.address_id as address_8_3_
from
    Customer_AUD c
inner join
    Address_AUD a
        on (
            c.address_id=a.id
            or (
                c.address_id is null
            )
            and (
                a.id is null
            )
        )
where
    c.REV<=?
    and c.REVTYPE<>?
    and (
        c.REVEND>?
        or c.REVEND is null
    )
    and a.REV<=?
    and a.country=?
    and (
        a.REVEND>?
        or a.REVEND is null
    )

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [VARCHAR] - [România]
-- binding parameter [6] as [INTEGER] - [1]

It is also possible to traverse beyond the first relation in an entity graph.

For example, to find all Customer entities at a given revision with the country attribute of the address property being România:

Example 686. Filtering a nested join relation with a WHERE clause predicate
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER)
.traverseRelation("country", JoinType.INNER)
.add(AuditEntity.property("name").eq("România"))
.getResultList();

assertEquals(1, customers.size());
select
    cu.id as id1_5_,
    cu.REV as REV2_5_,
    cu.REVTYPE as REVTYPE3_5_,
    cu.REVEND as REVEND4_5_,
    cu.created_on as created_5_5_,
    cu.firstName as firstNam6_5_,
    cu.lastName as lastName7_5_,
    cu.address_id as address_8_5_
from
    Customer_AUD cu
inner join
    Address_AUD a
        on (
            cu.address_id=a.id
            or (
                cu.address_id is null
            )
            and (
                a.id is null
            )
        )
inner join
    Country_AUD co
        on (
            a.country_id=co.id
            or (
                a.country_id is null
            )
            and (
                co.id is null
            )
        )
where
    cu.REV<=?
    and cu.REVTYPE<>?
    and (
        cu.REVEND>?
        or cu.REVEND is null
    )
    and a.REV<=?
    and (
        a.REVEND>?
        or a.REVEND is null
    )
    and co.REV<=?
    and co.name=?
    and (
        co.REVEND>?
        or co.REVEND is null
    )

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [INTEGER] - [1]
-- binding parameter [6] as [INTEGER] - [1]
-- binding parameter [7] as [VARCHAR] - [România]
-- binding parameter [8] as [INTEGER] - [1]

Constraints may also be added to the properties of nested joined relations, such as testing for null.

For example, the following query illustrates how to find all Customer entities at a given revision having the address in Cluj-Napoca or the address does not have any country entity reference:

Example 687. Filtering a join relation using multiple predicates
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.LEFT, "a")
.add(
	AuditEntity.or(
		AuditEntity.property("a", "city").eq("Cluj-Napoca"),
		AuditEntity.relatedId("country").eq(null)
	)
)
.getResultList();
select
  c.id as id1_5_,
  c.REV as REV2_5_,
  c.REVTYPE as REVTYPE3_5_,
  c.REVEND as REVEND4_5_,
  c.created_on as created_5_5_,
  c.firstName as firstNam6_5_,
  c.lastName as lastName7_5_,
  c.address_id as address_8_5_
from
  Customer_AUD c
left outer join
  Address_AUD a
    on (
      c.address_id=a.id
      or (
        c.address_id is null
      )
      and (
        a.id is null
      )
    )
where
  c.REV<=?
  and c.REVTYPE<>?
  and (
    c.REVEND>?
    or c.REVEND is null
  )
  and (
    a.REV is null
    or a.REV<=?
    and (
      a.REVEND>?
      or a.REVEND is null
    )
  )
  and (
    a.city=?
    or a.country_id is null
  )

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [INTEGER] - [1]
-- binding parameter [5] as [INTEGER] - [1]
-- binding parameter [6] as [VARCHAR] - [Cluj-Napoca]

Queries can use the up method to navigate back up the entity graph.

Disjunction criterion may also be applied to relation join queries.

For example, the following query will find all Customer entities at a given revision where the country name is România or that the Customer lives in Cluj-Napoca:

Example 688. Filtering a nested join relation using multiple predicates
List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, 1)
.traverseRelation("address", JoinType.INNER, "a")
.traverseRelation("country", JoinType.INNER, "cn")
.up()
.up()
.add(
	AuditEntity.disjunction()
	.add(AuditEntity.property("a", "city").eq("Cluj-Napoca"))
	.add(AuditEntity.property("cn", "name").eq("România"))
)
.addOrder(AuditEntity.property("createdOn").asc())
.getResultList();
select
    cu.id as id1_5_,
    cu.REV as REV2_5_,
    cu.REVTYPE as REVTYPE3_5_,
    cu.REVEND as REVEND4_5_,
    cu.created_on as created_5_5_,
    cu.firstName as firstNam6_5_,
    cu.lastName as lastName7_5_,
    cu.address_id as address_8_5_
from
    Customer_AUD cu
inner join
    Address_AUD a
        on (
            cu.address_id=a.id
            or (
                cu.address_id is null
            )
            and (
                a.id is null
            )
        )
inner join
    Country_AUD co
        on (
            a.country_id=co.id
            or (
                a.country_id is null
            )
            and (
                co.id is null
            )
        )
where
    cu.REV<=?
    and cu.REVTYPE<>?
    and (
        cu.REVEND>?
        or cu.REVEND is null
    )
    and (
        a.city=?
        or co.name=?
    )
    and a.REV<=?
    and (
        a.REVEND>?
        or a.REVEND is null
    )
    and co.REV<=?
    and (
        co.REVEND>?
        or co.REVEND is null
    )
order by
    cu.created_on asc

-- binding parameter [1] as [INTEGER] - [1]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [1]
-- binding parameter [4] as [VARCHAR] - [Cluj-Napoca]
-- binding parameter [5] as [VARCHAR] - [România]
-- binding parameter [6] as [INTEGER] - [1]
-- binding parameter [7] as [INTEGER] - [1]
-- binding parameter [8] as [INTEGER] - [1]
-- binding parameter [9] as [INTEGER] - [1]

Lastly, this example illustrates how related entity properties can be compared in a single constraint.

Assuming the Customer and the Address were previously changed as follows:

Example 689. Changing the Address to match the Country name
Customer customer = entityManager.createQuery(
	"select c " +
	"from Customer c " +
	"join fetch c.address a " +
	"join fetch a.country " +
	"where c.id = :id", Customer.class)
.setParameter("id", 1L)
.getSingleResult();

customer.setLastName("Doe Sr.");

customer.getAddress().setCity(
	customer.getAddress().getCountry().getName()
);

The following query shows how to find the Customer entities where the city property of the address attribute equals the name of the associated country attribute.

Example 690. Filtering a nested join relation using multiple predicates
List<Number> revisions = AuditReaderFactory.get(entityManager).getRevisions(
	Customer.class,
	1L
);

List<Customer> customers = AuditReaderFactory
.get(entityManager)
.createQuery()
.forEntitiesAtRevision(Customer.class, revisions.get(revisions.size() - 1))
.traverseRelation("address", JoinType.INNER, "a")
.traverseRelation("country", JoinType.INNER, "cn")
.up()
.up()
.add(AuditEntity.property("a", "city").eqProperty("cn", "name"))
.getResultList();
select
    cu.id as id1_5_,
    cu.REV as REV2_5_,
    cu.REVTYPE as REVTYPE3_5_,
    cu.REVEND as REVEND4_5_,
    cu.created_on as created_5_5_,
    cu.firstName as firstNam6_5_,
    cu.lastName as lastName7_5_,
    cu.address_id as address_8_5_
from
    Customer_AUD cu
inner join
    Address_AUD a
        on (
            cu.address_id=a.id
            or (
                cu.address_id is null
            )
            and (
                a.id is null
            )
        )
inner join
    Country_AUD cr
        on (
            a.country_id=cr.id
            or (
                a.country_id is null
            )
            and (
                cr.id is null
            )
        )
where
    cu.REV<=?
    and cu.REVTYPE<>?
    and a.city=cr.name
    and (
        cu.REVEND>?
        or cu.REVEND is null
    )
    and a.REV<=?
    and (
        a.REVEND>?
        or a.REVEND is null
    )
    and cr.REV<=?
    and (
        cr.REVEND>?
        or cr.REVEND is null
    )

-- binding parameter [1] as [INTEGER] - [2]
-- binding parameter [2] as [INTEGER] - [2]
-- binding parameter [3] as [INTEGER] - [2]
-- binding parameter [4] as [INTEGER] - [2]
-- binding parameter [5] as [INTEGER] - [2]
-- binding parameter [6] as [INTEGER] - [2]
-- binding parameter [7] as [INTEGER] - [2]

24.17. Querying for revision information without loading entities

Sometimes, it may be useful to load information about revisions to find out who performed specific revisions or to know what entity names were modified but the change log about the related audited entities isn’t needed. This API allows an efficient way to get the revision information entity log without instantiating the actual entities themselves.

Here is a simple example:

AuditQuery query = getAuditReader().createQuery()
    .forRevisionsOfEntity( DefaultRevisionEntity.class, true )
    .add( AuditEntity.revisionNumber().between( 1, 25 ) );

This query will return all revision information entities for revisions between 1 and 25 including those which are related to deletions. If deletions are not of interest, you would pass false as the second argument.

Note that this query uses the DefaultRevisionEntity class type. The class provided will vary depending on the configuration properties used to configure Envers or if you supply your own revision entity. Typically users who will use this API will likely be providing a custom revision entity implementation to obtain custom information being maintained per revision.

24.18. Conditional auditing

Envers persists audit data in reaction to various Hibernate events (e.g. post update, post insert, and so on), using a series of event listeners from the org.hibernate.envers.event.spi package. By default, if the Envers jar is in the classpath, the event listeners are auto-registered with Hibernate.

Conditional auditing can be implemented by overriding some of the Envers event listeners. To use customized Envers event listeners, the following steps are needed:

  1. Turn off automatic Envers event listeners registration by setting the hibernate.envers.autoRegisterListeners Hibernate property to false.

  2. Create subclasses for appropriate event listeners. For example, if you want to conditionally audit entity insertions, extend the org.hibernate.envers.event.spi.EnversPostInsertEventListenerImpl class. Place the conditional-auditing logic in the subclasses, call the super method if auditing should be performed.

  3. Create your own implementation of org.hibernate.integrator.spi.Integrator, similar to org.hibernate.envers.boot.internal.EnversIntegrator. Use your event listener classes instead of the default ones.

  4. For the integrator to be automatically used when Hibernate starts up, you will need to add a META-INF/services/org.hibernate.integrator.spi.Integrator file to your jar. The file should contain the fully qualified name of the class implementing the interface.

The use of hibernate.listeners.envers.autoRegister has been deprecated. The new hibernate.envers.autoRegisterListeners configuration setting should be used instead.

24.19. Understanding the Envers Schema

For each audited entity (that is, for each entity containing at least one audited field), an audit table is created. By default, the audit table’s name is created by adding an "_AUD" suffix to the original table name, but this can be overridden by specifying a different suffix/prefix in the configuration properties or per-entity using the @org.hibernate.envers.AuditTable annotation.

The audit table contains the following columns:

id

id of the original entity (this can be more then one column in the case of composite primary keys).

revision number

an integer, which matches to the revision number in the revision entity table.

revision type

The org.hibernate.envers.RevisionType enumeration ordinal stating if the change represents an INSERT, UPDATE or DELETE.

audited fields

properties from the original entity being audited.

The primary key of the audit table is the combination of the original id of the entity and the revision number, so there can be at most one historic entry for a given entity instance at a given revision.

The current entity data is stored in the original table and in the audit table. This is a duplication of data, however, as this solution makes the query system much more powerful, and as memory is cheap, hopefully, this won’t be a major drawback for the users.

A row in the audit table with entity id ID, revision N, and data D means: entity with id ID has data D from revision N upwards. Hence, if we want to find an entity at revision M, we have to search for a row in the audit table, which has the revision number smaller or equal to M, but as large as possible. If no such row is found, or a row with a "deleted" marker is found, it means that the entity didn’t exist at that revision.

The "revision type" field can currently have three values: 0, 1 and 2, which means ADD, MOD, and DEL, respectively. A row with a revision of type DEL will only contain the id of the entity and no data (all fields NULL), as it only serves as a marker saying "this entity was deleted at that revision".

Additionally, there is a revision entity table which contains the information about the global revision. By default, the generated table is named REVINFO and contains just two columns: ID and TIMESTAMP. A row is inserted into this table on each new revision, that is, on each commit of a transaction, which changes audited data. The name of this table can be configured, the name of its columns as well as adding additional columns can be achieved as discussed in Revision Log.

While global revisions are a good way to provide correct auditing of relations, some people have pointed out that this may be a bottleneck in systems where data is very often modified.

One viable solution is to introduce an option to have an entity "locally revisioned", that is revisions would be created for it independently. This would not enable correct versioning of relations, but it would work without the REVINFO table.

Another possibility is to introduce a notion of "revisioning groups", which would group entities sharing the same revision numbering. Each such group would have to consist of one or more strongly connected components belonging to the entity graph induced by relations between entities.

Your opinions on the subject are very welcome on the forum.

24.20. Generating Envers schema with Hibernate hbm2ddl tool

If you would like to generate the database schema file with Hibernate, you simply need to use the hbm2ddl tool.

This task will generate the definitions of all entities, both of those which are audited by Envers and those which are not.

See the Schema generation chapter for more info.

For the following entities, Hibernate is going to generate the following database schema:

Example 691. Filtering a nested join relation using multiple predicates
@Audited
@Entity(name = "Customer")
public static class Customer {

	@Id
	private Long id;

	private String firstName;

	private String lastName;

	@Temporal(TemporalType.TIMESTAMP)
	@Column(name = "created_on")
	@CreationTimestamp
	private Date createdOn;

	@ManyToOne(fetch = FetchType.LAZY)
	private Address address;

	//Getters and setters omitted for brevity
}

@Audited
@Entity(name = "Address")
public static class Address {

	@Id
	private Long id;

	@ManyToOne(fetch = FetchType.LAZY)
	private Country country;

	private String city;

	private String street;

	private String streetNumber;

	//Getters and setters omitted for brevity
}

@Audited
@Entity(name = "Country")
public static class Country {

	@Id
	private Long id;

	private String name;

	//Getters and setters omitted for brevity
}
create table Address (
    id bigint not null,
    city varchar(255),
    street varchar(255),
    streetNumber varchar(255),
    country_id bigint,
    primary key (id)
)

create table Address_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    REVEND integer,
    city varchar(255),
    street varchar(255),
    streetNumber varchar(255),
    country_id bigint,
    primary key (id, REV)
)

create table Country (
    id bigint not null,
    name varchar(255),
    primary key (id)
)

create table Country_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    REVEND integer,
    name varchar(255),
    primary key (id, REV)
)

create table Customer (
    id bigint not null,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    address_id bigint,
    primary key (id)
)

create table Customer_AUD (
    id bigint not null,
    REV integer not null,
    REVTYPE tinyint,
    REVEND integer,
    created_on timestamp,
    firstName varchar(255),
    lastName varchar(255),
    address_id bigint,
    primary key (id, REV)
)

create table REVINFO (
    REV integer generated by default as identity,
    REVTSTMP bigint,
    primary key (REV)
)

alter table Address
add constraint FKpr4rl83u5fv832kdihl6w3kii
foreign key (country_id)
references Country

alter table Address_AUD
add constraint FKgwp5sek4pjb4awy66sp184hrv
foreign key (REV)
references REVINFO

alter table Address_AUD
add constraint FK52pqkpismfxg2b9tmwtncnk0d
foreign key (REVEND)
references REVINFO

alter table Country_AUD
add constraint FKrix4g8hm9ui6sut5sy86ujggr
foreign key (REV)
references REVINFO

alter table Country_AUD
add constraint FKpjeqmdccv22y1lbtswjb84ghi
foreign key (REVEND)
references REVINFO

alter table Customer
add constraint FKfok4ytcqy7lovuiilldbebpd9
foreign key (address_id)
references Address

alter table Customer_AUD
add constraint FK5ecvi1a0ykunrriib7j28vpdj
foreign key (REV)
references REVINFO

alter table Customer_AUD
add constraint FKqd4fy7ww1yy95wi4wtaonre3f
foreign key (REVEND)
references REVINFO

24.21. Mapping exceptions

24.21.1. What isn’t and will not be supported

Bags are not supported because they can contain non-unique elements. Persisting a bag of `String`s violates the relational database principle that each table is a set of tuples.

In case of bags, however (which require a join table), if there is a duplicate element, the two tuples corresponding to the elements will be the same. Although Hibernate allows this, Envers (or more precisely the database connector) will throw an exception when trying to persist two identical elements because of a unique constraint violation.

There are at least two ways out if you need bag semantics:

  1. use an indexed collection, with the @jakarta.persistence.OrderColumn annotation.

  2. provide a unique id for your elements with the @CollectionId annotation.

24.21.2. What isn’t and will be supported

  • Bag style collections with a @CollectionId identifier column (see HHH-3950).

24.22. @OneToMany with @JoinColumn

When a collection is mapped using these two annotations, Hibernate doesn’t generate a join table. Envers, however, has to do this so that when you read the revisions in which the related entity has changed, you don’t get false results.

To be able to name the additional join table, there is a special annotation: @AuditJoinTable, which has similar semantics to Jakarta Persistence @JoinTable.

One special case is to have relations mapped with @OneToMany with @JoinColumn on the one side, and @ManyToOne and @JoinColumn( insertable = false, updatable = false) on the many side. Such relations are, in fact, bidirectional, but the owning side is the collection.

To properly audit such relations with Envers, you can use the @AuditMappedBy annotation. It enables you to specify the reverse property (using the mappedBy element). In case of indexed collections, the index column must also be mapped in the referenced entity (using @Column( insertable = false, updatable = false ), and specified using positionMappedBy. This annotation will affect only the way Envers works. Please note that the annotation is experimental and may change in the future.

24.23. Advanced: Audit table partitioning

24.24. Benefits of audit table partitioning

Because audit tables tend to grow indefinitely, they can quickly become really large. When the audit tables have grown to a certain limit (varying per RDBMS and/or operating system) it makes sense to start using table partitioning. SQL table partitioning offers a lot of advantages including, but certainly not limited to:

  1. Improved query performance by selectively moving rows to various partitions (or even purging old rows).

  2. Faster data loads, index creation, etc.

24.25. Suitable columns for audit table partitioning

Generally, SQL tables must be partitioned on a column that exists within the table. As a rule, it makes sense to use either the end revision or the end revision timestamp column for partitioning of audit tables.

End revision information is not available for the default AuditStrategy.

Therefore the following Envers configuration options are required:

org.hibernate.envers.audit_strategy = org.hibernate.envers.strategy.ValidityAuditStrategy

org.hibernate.envers.audit_strategy_validity_store_revend_timestamp = true

Optionally, you can also override the default values using following properties:

org.hibernate.envers.audit_strategy_validity_end_rev_field_name

org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name

org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric

For more information, see Configuration Properties.

The reason why the end revision information should be used for audit table partitioning is based on the assumption that audit tables should be partitioned on an 'increasing level of relevancy', like so:

  1. A couple of partitions with audit data that is not very (or no longer) relevant. This can be stored on slow media, and perhaps even be purged eventually.

  2. Some partitions for audit data that is potentially relevant.

  3. One partition for audit data that is most likely to be relevant. This should be stored on the fastest media, both for reading and writing.

24.26. Audit table partitioning example

In order to determine a suitable column for the 'increasing level of relevancy', consider a simplified example of a salary registration for an unnamed agency.

Currently, the salary table contains the following rows for a certain person X:

Table 9. Salaries table
Year Salary (USD)

2006

3300

2007

3500

2008

4000

2009

4500

The salary for the current fiscal year (2010) is unknown. The agency requires that all changes in registered salaries for a fiscal year are recorded (i.e., an audit trail). The rationale behind this is that decisions made at a certain date are based on the registered salary at that time. And at any time it must be possible to reproduce the reason why a certain decision was made at a certain date.

The following audit information is available, sorted in order of occurrence:

Table 10. Salaries - audit table
Year Revision type Revision timestamp Salary (USD) End revision timestamp

2006

ADD

2007-04-01

3300

null

2007

ADD

2008-04-01

35

2008-04-02

2007

MOD

2008-04-02

3500

null

2008

ADD

2009-04-01

3700

2009-07-01

2008

MOD

2009-07-01

4100

2010-02-01

2008

MOD

2010-02-01

4000

null

2009

ADD

2010-04-01

4500

null

24.27. Determining a suitable partitioning column

To partition this data, the level of relevancy must be defined. Consider the following:

  1. For the fiscal year 2006, there is only one revision. It has the oldest revision timestamp of all audit rows, but should still be regarded as relevant because it’s the latest modification for this fiscal year in the salary table (its end revision timestamp is null).

    Also, note that it would be very unfortunate if in 2011 there would be an update of the salary for the fiscal year 2006 (which is possible until at least 10 years after the fiscal year), and the audit information would have been moved to a slow disk (based on the age of the revision timestamp). Remember that, in this case, Envers will have to update the end revision timestamp of the most recent audit row.

  2. There are two revisions in the salary of the fiscal year 2007 which both have nearly the same revision timestamp and a different end revision timestamp.

On first sight, it is evident that the first revision was a mistake and probably not relevant. The only relevant revision for 2007 is the one with end revision timestamp value of null.

Based on the above, it is evident that only the end revision timestamp is suitable for audit table partitioning. The revision timestamp is not suitable.

24.28. Determining a suitable partitioning scheme

A possible partitioning scheme for the salary table would be as follows:

end revision timestamp year = 2008

This partition contains audit data that is not very (or no longer) relevant.

end revision timestamp year = 2009

This partition contains audit data that is potentially relevant.

end revision timestamp year >= 2010 or null

This partition contains the most relevant audit data.

This partitioning scheme also covers the potential problem of the update of the end revision timestamp, which occurs if a row in the audited table is modified. Even though Envers will update the end revision timestamp of the audit row to the system date at the instant of modification, the audit row will remain in the same partition (the 'extension bucket').

And sometime in 2011, the last partition (or 'extension bucket') is split into two new partitions:

  1. end revision timestamp year = 2010: This partition contains audit data that is potentially relevant (in 2011).

  2. end revision timestamp year >= 2011 or null: This partition contains the most interesting audit data and is the new 'extension bucket'.

  1. Hibernate main page

  2. Forum

  3. JIRA issue tracker (when adding issues concerning Envers, be sure to select the "envers" component!)

  4. Zulip channel

  5. FAQ

25. Managed Beans

Hibernate supports consuming many of its extension points as "managed beans". A bean being managed simply means that its creation and lifecycle are managed by a container of some sort.

The main contract for managed beans is org.hibernate.resource.beans.spi.ManagedBeanRegistry

Often these beans are managed by an external service, such as CDI. The contract org.hibernate.resource.beans.container.spi.BeanContainer is used to integrate the external container. ManagedBeanRegistry integrates support for a BeanContainer if one is specified.

By default, Hibernate creates references to the beans and links their lifecycle to the SessionFactory. It supports a number of ways to influence how this process works.

25.1. Manageable Beans

Jakarta Persistence defines support for resolving AttributeConverter and "entity listener" classes as managed beans.

Additionally, Hibernate supports resolving the following integrations as managed beans:

  • org.hibernate.type.descriptor.jdbc.JdbcType

  • org.hibernate.type.descriptor.java.BasicJavaType

  • org.hibernate.type.descriptor.java.MutabilityPlan

  • org.hibernate.usertype.UserType

  • org.hibernate.usertype.UserCollectionType

  • org.hibernate.metamodel.EmbeddableInstantiator

  • org.hibernate.envers.RevisionListener

  • org.hibernate.id.IdentifierGenerator

At the moment, when using either delayed or extended CDI access, resolving these Hibernate integrations as managed beans is disabled.

25.2. CDI BeanContainer

Hibernate provides built-in support for using a CDI BeanManager as the BeanContainer.

Jakarta Persistence indicates that the setting jakarta.persistence.bean.manager be used to pass along a CDI BeanManager to use, so Hibernate follows that approach.

25.2.1. CDI BeanManager - default

By default, Hibernate follows the Jakarta Persistence requirements for using CDI BeanManager. Most importantly, this means accessing beans from the BeanManager immediately during bootstrap.

In many cases this can cause circularity problems as CDI is often a consumer of persistence as well. In such cases, delayed or extended access should be used

25.2.2. CDI BeanManager - delayed

Rather than accessing the CDI managed beans immediately, Hibernate can be configured to delay accessing the beans until first needed using hibernate.delay_cdi_access.

Note however that this has some limitations{fn-cdi-availability}

25.2.3. CDI BeanManager - extended

Sometimes the actual BeanManager instance is not known until after Hibernate has been bootstrapped.

For such cases, Hibernate provides the org.hibernate.resource.beans.container.spi.ExtendedBeanManager contract, which is basically a promise or future for a BeanManager reference.

An instance of ExtendedBeanManager passed as jakarta.persistence.bean.manager triggers this behavior.

The ExtendedBeanManager implementation accepts the LifecycleListener passed to its #registerLifecycleListener method. It will call LifecycleListener#beanManagerInitialized and LifecycleListener#beforeBeanManagerDestroyed as lifecycle callbacks for the real BeanManager.

Hibernate uses the LifecycleListener#beanManagerInitialized callback to get access to the real BeanManager.

When used in WildFly, this is all automatically set up by the server

25.3. Custom BeanContainer

Other containers (Spring, e.g.) can also be used and integrated by implementing BeanContainer and declaring it using hibernate.resource.beans.container.

26. Database Portability Considerations

26.1. Portability Basics

One of the selling points of Hibernate (and really Object/Relational Mapping as a whole) is the notion of database portability. This could mean an internal IT user migrating from one database vendor to another, or it could mean a framework or deployable application consuming Hibernate to simultaneously target multiple database products by their users. Regardless of the exact scenario, the basic idea is that you want Hibernate to help you run against any number of databases without changes to your code, and ideally without any changes to the mapping metadata.

26.2. Dialect

The first line of portability for Hibernate is the dialect, which is a specialization of the org.hibernate.dialect.Dialect contract. A dialect encapsulates all the differences in how Hibernate must communicate with a particular database to accomplish some task like getting a sequence value or structuring a SELECT query. Hibernate bundles a wide range of dialects for many of the most popular databases. If you find that your particular database is not among them, it is not terribly difficult to write your own.

26.3. Dialect resolution

Originally, Hibernate would always require that users specify which dialect to use. In the case of users looking to simultaneously target multiple databases with their build that was problematic. Generally, this required their users to configure the Hibernate dialect or defining their own method of setting that value.

Starting with version 3.2, Hibernate introduced the notion of automatically detecting the dialect to use based on the java.sql.DatabaseMetaData obtained from a java.sql.Connection to that database. This was much better, except that this resolution was limited to databases Hibernate know about ahead of time and was in no way configurable or overrideable.

Starting with version 3.3, Hibernate has a far more powerful way to automatically determine which dialect to be used by relying on a series of delegates which implement the org.hibernate.dialect.resolver.DialectResolver which defines only a single method:

public Dialect resolveDialect(DatabaseMetaData metaData) throws JDBCConnectionException

The basic contract here is that if the resolver 'understands' the given database metadata then it returns the corresponding Dialect; if not it returns null and the process continues to the next resolver. The signature also identifies org.hibernate.exception.JDBCConnectionException as possibly being thrown. A JDBCConnectionException here is interpreted to imply a non-transient (aka non-recoverable) connection problem and is used to indicate an immediate stop to resolution attempts. All other exceptions result in a warning and continuing on to the next resolver.

The cool part about these resolvers is that users can also register their own custom resolvers which will be processed ahead of the built-in Hibernate ones. This might be useful in a number of different situations:

  • it allows easy integration for auto-detection of dialects beyond those shipped with Hibernate itself.

  • it allows you to specify to use a custom dialect when a particular database is recognized.

To register one or more resolvers, simply specify them (separated by commas, tabs or spaces) using the 'hibernate.dialect_resolvers' configuration setting (see the DIALECT_RESOLVERS constant on org.hibernate.cfg.Environment).

26.4. Identifier generation

When considering portability between databases, another important decision is selecting the identifier generation strategy you want to use. Originally, Hibernate provided the native generator for this purpose, which was intended to select between a sequence, identity, or table strategy depending on the capability of the underlying database.

However, an insidious implication of this approach comes about when targeting some databases which support identity generation and some which do not. identity generation relies on the SQL definition of an IDENTITY (or auto-increment) column to manage the identifier value. It is what is known as a post-insert generation strategy because the insert must actually happen before we can know the identifier value.

Because Hibernate relies on this identifier value to uniquely reference entities within a persistence context, it must then issue the insert immediately when the user requests that the entity be associated with the session (e.g. like via save() or persist()), regardless of current transactional semantics.

Hibernate was changed slightly, once the implications of this were better understood, so now the insert could be delayed in cases where this is feasible.

The underlying issue is that the actual semantics of the application itself changes in these cases.

Starting with version 3.2.3, Hibernate comes with a set of enhanced identifier generators targeting portability in a much different way.

There are specifically 2 bundled enhanced generators:

  • org.hibernate.id.enhanced.SequenceStyleGenerator

  • org.hibernate.id.enhanced.TableGenerator

The idea behind these generators is to port the actual semantics of the identifier value generation to the different databases. For example, the org.hibernate.id.enhanced.SequenceStyleGenerator mimics the behavior of a sequence on databases which do not support sequences by using a table.

26.5. Database functions

HQL now provides a large set of functions which are portable between databases. You can find them listed in the chapter describing the query language. There’s even a way for a program to contribute its own function definitions.

Of course, SQL functions occurring in handwritten SQL fragments or queries usually aren’t very portable.

26.6. Type mappings

TODO

26.6.1. BLOB/CLOB mappings

TODO

26.6.2. Boolean mappings

26.6.3. Jakarta Persistence portability

  • HQL/JPQL differences

  • naming strategies

  • basic types

  • simple id types

  • generated id types

  • composite ids and many-to-one

  • "embedded composite identifiers"

27. Statistics

Hibernate can gather all sorts of statistics which can help you get a better insight into what Hibernate does behind the scenes.

By default, the statistics are not collected because this incurs an additional processing and memory overhead. To instruct Hibernate to start collecting statistics, you need to set the hibernate.generate_statistics configuration property to true:

<property
    name="hibernate.generate_statistics"
    value="true"
/>

27.1. org.hibernate.stat.Statistics methods

The Hibernate statistics are made available via the Statistics interface which exposes the following methods:

27.1.1. General statistics methods

isStatisticsEnabled

Are statistics enabled?

setStatisticsEnabled(boolean b)

Enable statistics based on the provided parameter.

clear

Reset all statistics.

logSummary

Print a summary of the current statistics into the application log.

getStartTime

The milliseconds (JVM standard currentTimeMillis()) since the initial creation of this Statistics instance or the last time clear() was called.

27.1.2. Aggregated statistics methods

getQueries

Get executed query strings. The maximum number of queries tracked by the Hibernate statistics is given by the hibernate.statistics.query_max_size property.

getEntityStatistics(String entityName)

Find entity statistics for the given name.

getCollectionStatistics(String role)

Get collection statistics per role (collection name).

getNaturalIdStatistics(String entityName)

Get the Hibernate-specific natural id resolution statistics for the given entity.

getQueryStatistics(String queryString)

Get the statistics for the given query string (JPQL/HQL or native SQL).

getDomainDataRegionStatistics(String regionName)

Get the second-level cache statistics per domain data (entity, collection, natural-id) region.

getQueryRegionStatistics(String regionName)

Get the second-level cache statistics per query region.

getCacheRegionStatistics(String regionName)

Get statistics for either a domain-data or query-result region (this method checks both, preferring domain data region if one exists).

27.1.3. SessionFactory statistics methods

getEntityNames

Get the names of all entities configured with the current SessionFactory.

getCollectionRoleNames

Get the names of all collection roles configured with the current SessionFactory.

27.1.4. Session statistics methods

getSessionCloseCount

Global number of sessions that got closed.

getSessionOpenCount

Global number of sessions that got opened.

getFlushCount

Get the global number of flush operations executed (either manual or automatic).

27.1.5. JDBC statistics methods

getPrepareStatementCount

The number of JDBC prepared statements that were acquired by Hibernate.

getCloseStatementCount

The number of JDBC prepared statements that were released by Hibernate.

getConnectCount

Get the global number of connections acquired by the Hibernate sessions (the actual number of connections used may be much smaller depending whether you use a connection pool or not).

27.1.6. Transaction statistics methods

getSuccessfulTransactionCount

The number of transactions that completed successfully.

getTransactionCount

The number of transactions we know to have completed.

27.1.7. Concurrency Control statistics methods

getOptimisticFailureCount

The number of Hibernate StaleObjectStateExceptions or Jakarta Persistence OptimisticEntityLockExceptions that occurred.

27.1.8. Entity statistics methods

getEntityDeleteCount

Get the global number of entity deletes.

getEntityInsertCount

Get the global number of entity inserts.

getEntityLoadCount

Get the global number of entity loads.

getEntityFetchCount

Get the global number of entity fetches.

getEntityUpdateCount

Get the global number of entity updates.

27.1.9. Collection statistics methods

getCollectionLoadCount

Global number of collections that were loaded.

getCollectionFetchCount

Global number of collections that were fetched.

getCollectionUpdateCount

Global number of collections that were updated.

getCollectionRemoveCount

Global number of collections that were removed.

getCollectionRecreateCount

Global number of collections that were recreated.

27.1.10. Query statistics methods

getQueryExecutionCount

Get the global number of executed queries.

getQueryExecutionMaxTime

Get the time in milliseconds of the slowest query.

getQueryExecutionMaxTimeQueryString

Get the query string for the slowest query.

getQueryPlanCacheHitCount

Get the global number of query plans successfully retrieved from cache.

getQueryPlanCacheMissCount

Get the global number of query plans lookups not found in cache.

27.1.11. Natural id statistics methods

getNaturalIdQueryExecutionCount

Get the global number of natural id queries executed against the database.

getNaturalIdQueryExecutionMaxTime

Get the global maximum query time for natural id queries executed against the database.

getNaturalIdQueryExecutionMaxTimeRegion

Get the region for the maximum natural id query time.

getNaturalIdQueryExecutionMaxTimeEntity

Get the entity for the maximum natural id query time.

27.1.12. Second-level cache statistics methods

getSecondLevelCacheRegionNames

Get all second-level domain data cache region names.

getSecondLevelCacheHitCount

Global number of cacheable entities/collections successfully retrieved from the cache.

getSecondLevelCacheMissCount

Global number of cacheable entities/collections not found in the cache and loaded from the database.

getSecondLevelCachePutCount

Global number of cacheable entities/collections put in the cache.

Second-level cache natural id statistics methods
getNaturalIdCacheHitCount

Get the global number of cached natural id lookups successfully retrieved from cache.

getNaturalIdCacheMissCount

Get the global number of cached natural id lookups not found in cache.

getNaturalIdCachePutCount

Get the global number of cacheable natural id lookups put in cache.

Second-level cache query statistics methods
getQueryCacheHitCount

Get the global number of cached queries successfully retrieved from cache.

getQueryCacheMissCount

Get the global number of cached queries not found in cache.

getQueryCachePutCount

Get the global number of cacheable queries put in cache.

Second-level cache timestamp statistics methods
getUpdateTimestampsCacheHitCount

Get the global number of timestamps successfully retrieved from cache.

getUpdateTimestampsCacheMissCount

Get the global number of timestamp requests that were not found in the cache.

getUpdateTimestampsCachePutCount

Get the global number of timestamps put in cache.

27.2. Query statistics max size

Traditionally, Hibernate stored all executed queries when statistics were enabled. However, this was a very bad default since, if your application runs millions of different queries, you’d risk running out of memory.

Therefore, to restrict the number of queries the Hibernate statistics can hold, the hibernate.statistics.query_max_size property was added. By default, the maximum number of queries retained is 5000, but you can increase this value via the hibernate.statistics.query_max_size property.

So, if your application makes heavy use of the Jakarta Persistence Criteria API or if you simply have a very large number of queries, you might want to raise the maximum number of queries that are being stored by the Statistics instance.

If the maximum number of queries has been reached, Hibernate uses a Least recently used (LRU) policy to make room for new query entries.

27.3. Query plan cache statistics

Every entity query, be it JPQL/HQL or Criteria API, is compiled to an AST (Abstract Syntax Tree), and this process is resource-intensive. To speed up the entity query executions, Hibernate offers a query plan cache so that compiled plans can be reused.

To monitor the query plan cache you have the following statistics.

27.3.1. Query plan cache global statistics

The Statistics instance provides two global counters which can give you an overall picture of the query plan cache effectiveness.

  • getQueryPlanCacheHitCount

  • getQueryPlanCacheMissCount

If the hit count is high and the miss count is low, then the query plan cache is effective, and the vast majority of entity queries are served from the query plan cache, rather than being compiled over and over again.

27.3.2. Query plan cache query-level statistics

The QueryStatistics instance, which you can get via the getQueryStatistics(String queryString) method of the Statistics object, stores the following query plan cache metrics:

getPlanCacheHitCount

The number of query plans successfully fetched from the cache.

getQueryPlanCacheMissCount

The number of query plans not fetched from the cache.

getPlanCompilationTotalMicroseconds

The overall time spent to compile the plan for this particular query.

28. Build Tool Integration

Hibernate provides build-time services available as plugins for

These services include

28.1. Bytecode Enhancement

Hibernate performs bytecode enhancement through its org.hibernate.bytecode.enhance.spi.Enhancer contract. These build time tools provide a way to incorporate configuration and execution of the enhancer into a build.

See Bytecode Enhancement for discussion of the capabilities of an enhanced model.

At the moment, only annotated classes are supported for enhancement.

28.1.1. Runtime Bytecode Enhancement

Hibernate can also perform run-time bytecode enhancement when used in Jakarta EE compliant containers through jakarta.persistence.spi.ClassTransformer. See the documentation of your container for any additional details. Run-time enhancement is controlled through 3 true/false settings (all of which default to false):

hibernate.enhancer.enableDirtyTracking

Whether to enhance the model for dirty-tracking. This setting is deprecated for removal without a replacement.

hibernate.enhancer.enableLazyInitialization

Whether to enhance the model for lazy loading at the attribute level. This allows even basic types to be fetched lazily. It also allows definition of fetch groups (LazyGroup). This setting is deprecated for removal without a replacement.

hibernate.enhancer.enableAssociationManagement

Whether to automatically synchronize a bidirectional association when only one side is changed.

28.2. Static Metamodel Generator

Jakarta Persistence defines a typesafe Criteria API which allows Criteria queries to be constructed in a strongly-typed manner, utilizing so-called static metamodel classes. The Hibernate Static Metamodel Generator, available via the published org.hibernate.orm:hibernate-jpamodelgen artifact, is an annotation processor used to generate these static metamodel classes.

The Hibernate Static Metamodel Generator has many additional capabilities beyond static metamodel class generation. See the Introduction Guide for a complete discussion of its capabilities. The rest of the discussion here is limited to the Jakarta Persistence static metamodel.

The generator is expected to be run using the javac -processorpath option. See the tool-specific discussions (Gradle, Maven and Ant) for details on integrating the generator into those environments.

28.2.1. Metamodel classes

The structure of the metamodel classes is described in the Jakarta Persistence specification, but for completeness the definition is repeated in the following paragraphs. For every class in a persistence-unit, the generator will produce a static metamodel class based on the following rules:

  • For each managed class X in package p, a metamodel class X_ is created in package p.

  • The name of the metamodel class is derived from the name of the managed class by appending "_" to the managed class name.

  • The metamodel class X_ must be annotated with the jakarta.persistence.StaticMetamodel annotation. The generation can also be configured to add the javax.annotation.processing.Generated annotation.

  • If class X extends another class S, where S is the most derived managed class extended by X, then class X_ must extend class S_, where S_ is the metamodel class created for S.

  • For every persistent singular attribute y declared by class X, where the type of y is Y, the metamodel class must contain a declaration as follows:

    public static volatile SingularAttribute<X, Y> y;
  • For every persistent plural attribute z declared by class X, where the element type of z is Z, the metamodel class must contain a declaration as follows:

    • if the collection type of z is java.util.Collection, then

      public static volatile CollectionAttribute<X, Z> z;
    • if the collection type of z is java.util.Set, then

      public static volatile SetAttribute<X, Z> z;
    • if the collection type of z is java.util.List, then

      public static volatile ListAttribute<X, Z> z;
    • if the collection type of z is java.util.Map, then

      public static volatile MapAttribute<X, K, Z> z;

      where K is the type of the key of the map in class X

  • Import statements must be included for jakarta.persistence.metamodel types as needed, as well as all domain model classes (i.e., X, S, Y, Z, and K).

As an example, consider the following domain model -

Example 692. Order and Item entities
@Entity
public class Customer {
	@Id
	private Integer id;
	@Basic
	private String name;

	// getters and setters omitted for brevity
}
@Entity
@Table(name = "orders")
public class Order {
	@Id
	Integer id;

	@ManyToOne
	Customer customer;

	@OneToMany
	Set<Item> items;
	BigDecimal totalCost;

	// standard setter/getter methods

}
@Entity
public class Item {
	@Id
	Integer id;

	int quantity;

	@ManyToOne
	Order order;

	// getters and setters omitted for brevity
}

Given this model, the generator will produce classes named Customer_, Order_ and Item_. As an example:

Example 693. Order_
package org.hibernate.testing.orm.domain.userguide.tooling;

import jakarta.annotation.Generated;
import jakarta.persistence.metamodel.EntityType;
import jakarta.persistence.metamodel.SetAttribute;
import jakarta.persistence.metamodel.SingularAttribute;
import jakarta.persistence.metamodel.StaticMetamodel;
import java.math.BigDecimal;

@StaticMetamodel(Order.class)
@Generated("org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
public abstract class Order_ {


	/**
	 * @see org.hibernate.testing.orm.domain.userguide.tooling.Order#id
	 **/
	public static volatile SingularAttribute<Order, Integer> id;

	/**
	 * @see org.hibernate.testing.orm.domain.userguide.tooling.Order
	 **/
	public static volatile EntityType<Order> class_;

	/**
	 * @see org.hibernate.testing.orm.domain.userguide.tooling.Order#items
	 **/
	public static volatile SetAttribute<Order, Item> items;

	/**
	 * @see org.hibernate.testing.orm.domain.userguide.tooling.Order#totalCost
	 **/
	public static volatile SingularAttribute<Order, BigDecimal> totalCost;

	/**
	 * @see org.hibernate.testing.orm.domain.userguide.tooling.Order#customer
	 **/
	public static volatile SingularAttribute<Order, Customer> customer;

	public static final String ID = "id";
	public static final String ITEMS = "items";
	public static final String TOTAL_COST = "totalCost";
	public static final String CUSTOMER = "customer";

}

At boot-time, Hibernate will find these classes and populate them. They can then be used in Criteria queries for type-safe path references. For example:

Example 694. Static Metamodel usage
final CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
final CriteriaQuery<Customer> criteria = criteriaBuilder.createQuery( Customer.class );

final Root<Order> root = criteria.from( Order.class );

criteria.select( root.get( Order_.customer ) );
criteria.where( criteriaBuilder.greaterThan( root.get( Order_.totalCost ), new BigDecimal( 100 ) ) );

28.2.2. Generation Options

The Hibernate Static Metamodel Generator accepts a number of configuration options, which are specified as part of the javac execution using standard -A options -

-Adebug=[true|false]

Enables debug logging from the generator.

-AfullyAnnotationConfigured=[true|false]

Controls whether orm.xml mapping should be considered.

-ApersistenceXml=[path]

Specifies the path to the persistence.xml file.

-AormXml=[path]

Specifies the path to an orm.xml file.

-AlazyXmlParsing=[true|false]

Controls whether the processor should attempt to determine whether any orm.xml files have changed.

-AaddGeneratedAnnotation=[true|false]

Controls whether the processor should add @jakarta.annotation.Generated to the generated classes.

-addGenerationDate=[true|false]

Controls whether the processor should add @jakarta.annotation.Generated#date.

-addSuppressWarningsAnnotation=[true|false]

Controls whether the processor should add @SuppressWarnings({"deprecation","rawtypes"}) to the generated classes.

28.3. Schema Management

Coming soon

28.4. Gradle

Hibernate provides the ability to integrate both bytecode enhancement and metamodel generation capabilities into Gradle builds.

28.4.1. Bytecode Enhancement

Bytecode enhancement is incorporated into Gradle builds using Hibernate’s Gradle plugin. To apply the plugin, use Gradle’s plugins {} block:

plugins {
    id "org.hibernate.orm" version "<version-to-use>"
}

Applying the plugin creates a hibernate extension (HibernateOrmSpec) to configure the plugin.

hibernate {
    ...
}

Enhancement is configured through the enhancement extension.

hibernate {} and enhancement {} are separate to allow for schema tooling capabilities to be added later.
hibernate {
    enhancement {
        // for illustration, enable them all
        lazyInitialization true
        dirtyTracking true
        associationManagement true
    }
}

The extension is of type EnhancementSpec which exposes the following properties:

enableLazyInitialization

Whether to incorporate lazy loading support into the enhanced bytecode. Defaults to true. This setting is deprecated for removal without a replacement. See Lazy attribute loading

enableDirtyTracking

Whether to incorporate dirty tracking into the enhanced bytecode. Defaults to true. This setting is deprecated for removal without a replacement. See In-line dirty tracking.

enableAssociationManagement

Whether to add bidirectional association management into the enhanced bytecode. See Bidirectional association management.

It also exposes the following method forms:

  • lazyInitialization(boolean)

  • dirtyTracking(boolean)

  • associationManagement(boolean)

28.4.2. Static Metamodel Generation

Static metamodel generation can be incorporated into Gradle builds via the annotation processor provided by the org.hibernate.orm:hibernate-jpamodelgen artifact. Applying an annotation processor in Gradle is super easy -

dependencies {
    annotationProcessor "org.hibernate.orm:hibernate-jpamodelgen:${hibernateVersion}"
}

28.5. Maven

The following sections illustrate how both bytecode enhancement and metamodel generation capabilities can be integrated into Maven builds.

28.5.1. Bytecode Enhancement

Hibernate provides a Maven plugin capable of providing build-time enhancement of the domain model as they are compiled as part of a Maven build. See the section on Bytecode Enhancement for details on the configuration settings. By default, all enhancements are disabled.

Example 695. Apply the Bytecode Enhancement plugin
<build>
    <plugins>
        [...]
        <plugin>
            <groupId>org.hibernate.orm.tooling</groupId>
            <artifactId>hibernate-enhance-maven-plugin</artifactId>
            <version>$currentHibernateVersion</version>
            <executions>
                <execution>
                    <configuration>
                        <failOnError>true</failOnError>
                        <enableLazyInitialization>true</enableLazyInitialization>
                        <enableDirtyTracking>true</enableDirtyTracking>
                        <enableAssociationManagement>true</enableAssociationManagement>
                    </configuration>
                    <goals>
                        <goal>enhance</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
        [...]
    </plugins>
</build>

28.5.2. Static Metamodel Generation

Static metamodel generation should be integrated into a maven project through the annotation processor paths of the maven compiler plugin.

Example 696. Integrate the metamodel generator
<build>
    <plugins>
        [...]
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>...</version>
            <configuration>
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.hibernate.orm</groupId>
                        <artifactId>hibernate-jpamodelgen</artifactId>
                        <version>$currentHibernateVersion</version>
                        <!-- Optionally exclude transitive dependencies -->
                        <exclusions>
                            <exclusion>
                                <groupId>org.sample</groupId>
                                <artifactId>sample-dependency</artifactId>
                            </exclusion>
                        </exclusions>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
        [...]
    </plugins>
</build>

28.6. Ant Plugin

Hibernate provides Ant support …​

28.6.1. Static Metamodel Generation in Ant

As mentioned in Static Metamodel Generator, the generator is implemented as an annotation processor and can be used anywhere javac is used - such as Ant’s javac task.

Example 697. Javac task configuration
<javac srcdir="${src.dir}"
        destdir="${target.dir}"
        failonerror="false"
        fork="true"
        classpath="${classpath}">
    <compilerarg value="-processorpath" />
    <compilerarg value="/path/to/metamodel-generator.jar"/>
    <compilerarg value="-proc:only"/>
</javac>

28.6.2. Schema Management

Coming soon

29. Performance Tuning and Best Practices

Every enterprise system is unique. However, having a very efficient data access layer is a common requirement for many enterprise applications. Hibernate comes with a great variety of features that can help you tune the data access layer.

29.1. Schema management

Although Hibernate provides the update option for the hibernate.hbm2ddl.auto configuration property, this feature is not suitable for a production environment.

An automated schema migration tool (e.g. Flyway, Liquibase) allows you to use any database-specific DDL feature (e.g. Rules, Triggers, Partitioned Tables). Every migration should have an associated script, which is stored on the Version Control System, along with the application source code.

When the application is deployed on a production-like QA environment, and the deployment worked as expected, then pushing the deployment to a production environment should be straightforward since the latest schema migration was already tested.

You should always use an automatic schema migration tool and have all the migration scripts stored in the Version Control System.

29.2. Logging

Whenever you’re using a framework that generates SQL statements on your behalf, you have to ensure that the generated statements are the ones that you intended in the first place.

There are several alternatives to logging statements. You can log statements by configuring the underlying logging framework. For Log4j, you can use the following appenders:

### log just the SQL
log4j.logger.org.hibernate.SQL=debug

### log JDBC bind parameters and extracted values ###
log4j.logger.org.hibernate.type=trace
log4j.logger.org.hibernate.orm.jdbc.bind=trace
log4j.logger.org.hibernate.orm.jdbc.extract=trace

However, there are some other alternatives like using datasource-proxy or p6spy. The advantage of using a JDBC Driver or DataSource proxy is that you can go beyond simple SQL logging:

Another advantage of using a DataSource proxy is that you can assert the number of executed statements at test time. This way, you can have the integration tests fail when a N+1 query issue is automatically detected.

While simple statement logging is fine, using datasource-proxy or p6spy is even better.

29.3. JDBC batching

JDBC allows us to batch multiple SQL statements and to send them to the database server into a single request. This saves database roundtrips, and so it reduces response time significantly.

Not only INSERT and UPDATE statements, but even DELETE statements can be batched as well. For INSERT and UPDATE statements, make sure that you have all the right configuration properties in place, like ordering inserts and updates and activating batching for versioned data. Check out this article for more details on this topic.

For DELETE statements, there is no option to order parent and child statements, so cascading can interfere with the JDBC batching process.

Unlike any other framework which doesn’t automate SQL statement generation, Hibernate makes it very easy to activate JDBC-level batching as indicated in the Batching chapter.

29.4. Mapping

Choosing the right mappings is very important for a high-performance data access layer. From the identifier generators to associations, there are many options to choose from, yet not all choices are equal from a performance perspective.

29.4.1. Identifiers

When it comes to identifiers, you can either choose a natural id or a synthetic key.

For natural identifiers, the assigned identifier generator is the right choice.

For synthetic keys, the application developer can either choose a randomly generated fixed-size sequence (e.g. UUID) or a natural identifier. Natural identifiers are very practical, being more compact than their UUID counterparts, so there are multiple generators to choose from:

  • IDENTITY

  • SEQUENCE

  • TABLE

Although the TABLE generator addresses the portability concern, in reality, it performs poorly because it requires emulating a database sequence using a separate transaction and row-level locks. For this reason, the choice is usually between IDENTITY and SEQUENCE.

If the underlying database supports sequences, you should always use them for your Hibernate entity identifiers.

Only if the relational database does not support sequences (e.g. MySQL 5.7), you should use the IDENTITY generators. However, you should keep in mind that the IDENTITY generators disables JDBC batching for INSERT statements.

If you’re using the SEQUENCE generator, then you should be using the enhanced identifier generators that were enabled by default in Hibernate 5. The pooled and the pooled-lo optimizers are very useful to reduce the number of database roundtrips when writing multiple entities per database transaction.

29.4.2. Associations

Jakarta Persistence offers four entity association types:

  • @ManyToOne

  • @OneToOne

  • @OneToMany

  • @ManyToMany

And an @ElementCollection for collections of embeddables.

Because object associations can be bidirectional, there are many possible combinations of associations. However, not every possible association type is efficient from a database perspective.

The closer the association mapping is to the underlying database relationship, the better it will perform.

On the other hand, the more exotic the association mapping, the better the chance of being inefficient.

Therefore, the @ManyToOne and the @OneToOne child-side association are best to represent a FOREIGN KEY relationship.

The parent-side @OneToOne association requires bytecode enhancement so that the association can be loaded lazily. Otherwise, the parent-side association is always fetched even if the association is marked with FetchType.LAZY.

For this reason, it’s best to map @OneToOne association using @MapsId so that the PRIMARY KEY is shared between the child and the parent entities. When using @MapsId, the parent-side association becomes redundant since the child-entity can be easily fetched using the parent entity identifier.

For collections, the association can be either:

  • unidirectional

  • bidirectional

For unidirectional collections, Sets are the best choice because they generate the most efficient SQL statements. Unidirectional Lists are less efficient than a @ManyToOne association.

Bidirectional associations are usually a better choice because the @ManyToOne side controls the association.

Embeddable collections (@ElementCollection) are unidirectional associations, hence Sets are the most efficient, followed by ordered Lists, whereas bags (unordered Lists) are the least efficient.

The @ManyToMany annotation is rarely a good choice because it treats both sides as unidirectional associations.

For this reason, it’s much better to map the link table as depicted in the Bidirectional many-to-many with link entity lifecycle section. Each FOREIGN KEY column will be mapped as a @ManyToOne association. On each parent-side, a bidirectional @OneToMany association is going to map to the aforementioned @ManyToOne relationship in the link entity.

Just because you have support for collections, it does not mean that you have to turn any one-to-many database relationship into a collection.

Sometimes, a @ManyToOne association is sufficient, and the collection can be simply replaced by an entity query which is easier to paginate or filter.

29.5. Inheritance

Jakarta Persistence offers SINGLE_TABLE, JOINED, and TABLE_PER_CLASS to deal with inheritance mapping, and each of these strategies has advantages and disadvantages.

  • SINGLE_TABLE performs the best in terms of executed SQL statements. However, you cannot use NOT NULL constraints on the column-level. You can still use triggers and rules to enforce such constraints, but it’s not as straightforward.

  • JOINED addresses the data integrity concerns because every subclass is associated with a different table. Polymorphic queries or @OneToMany base class associations don’t perform very well with this strategy. However, polymorphic @ManyToOne associations are fine, and they can provide a lot of value.

  • TABLE_PER_CLASS should be avoided since it does not render efficient SQL statements.

29.6. Fetching

Fetching too much data is the number one performance issue for the vast majority of Jakarta Persistence applications.

Hibernate supports both entity queries (JPQL/HQL and Criteria API) and native SQL statements. Entity queries are useful only if you need to modify the fetched entities, therefore benefiting from the automatic dirty checking mechanism.

For read-only transactions, you should fetch DTO projections because they allow you to select just as many columns as you need to fulfill a certain business use case. This has many benefits like reducing the load on the currently running Persistence Context because DTO projections don’t need to be managed.

29.6.1. Fetching associations

Related to associations, there are two major fetch strategies:

  • EAGER

  • LAZY

EAGER fetching is almost always a bad choice.

Prior to Jakarta Persistence, Hibernate used to have all associations as LAZY by default. However, when Java Persistence 1.0 specification emerged, it was thought that not all providers would use Proxies. Hence, the @ManyToOne and the @OneToOne associations are now EAGER by default.

The EAGER fetching strategy cannot be overwritten on a per query basis, so the association is always going to be retrieved even if you don’t need it. Moreover, if you forget to JOIN FETCH an EAGER association in a JPQL query, Hibernate will initialize it with a secondary statement, which in turn can lead to N+1 query issues.

So, EAGER fetching is to be avoided. For this reason, it’s better if all associations are marked as LAZY by default.

However, LAZY associations must be initialized prior to being accessed. Otherwise, a LazyInitializationException is thrown. There are good and bad ways to treat the LazyInitializationException.

The best way to deal with LazyInitializationException is to fetch all the required associations prior to closing the Persistence Context. The JOIN FETCH directive is good for @ManyToOne and OneToOne associations, and for at most one collection (e.g. @OneToMany or @ManyToMany). If you need to fetch multiple collections, to avoid a Cartesian Product, you should use secondary queries which are triggered either by navigating the LAZY association or by calling Hibernate#initialize(Object proxy) method.

29.7. Caching

Hibernate has two caching layers:

  • the first-level cache (Persistence Context) which provides application-level repeatable reads.

  • the second-level cache which, unlike application-level caches, doesn’t store entity aggregates but normalized dehydrated entity entries.

The first-level cache is not a caching solution "per se", being more useful for ensuring READ COMMITTED isolation level.

While the first-level cache is short-lived, being cleared when the underlying EntityManager is closed, the second-level cache is tied to an EntityManagerFactory. Some second-level caching providers offer support for clusters. Therefore, a node needs only to store a subset of the whole cached data.

Although the second-level cache can reduce transaction response time since entities are retrieved from the cache rather than from the database, there are other options to achieve the same goal, and you should consider these alternatives prior to jumping to a second-level cache layer:

  • tuning the underlying database cache so that the working set fits into memory, therefore reducing Disk I/O traffic.

  • optimizing database statements through JDBC batching, statement caching, indexing can reduce the average response time, therefore increasing throughput as well.

  • database replication is also a very valuable option to increase read-only transaction throughput.

After properly tuning the database, to further reduce the average response time and increase the system throughput, application-level caching becomes inevitable.

Typically, a key-value application-level cache like Memcached or Redis is a common choice to store data aggregates. If you can duplicate all data in the key-value store, you have the option of taking down the database system for maintenance without completely losing availability since read-only traffic can still be served from the cache.

One of the main challenges of using an application-level cache is ensuring data consistency across entity aggregates. That’s where the second-level cache comes to the rescue. Being tightly integrated with Hibernate, the second-level cache can provide better data consistency since entries are cached in a normalized fashion, just like in a relational database. Changing a parent entity only requires a single entry cache update, as opposed to cache entry invalidation cascading in key-value stores.

The second-level cache provides four cache concurrency strategies:

  • READ_ONLY

  • NONSTRICT_READ_WRITE

  • READ_WRITE

  • TRANSACTIONAL

READ_WRITE is a very good default concurrency strategy since it provides strong consistency guarantees without compromising throughput. The TRANSACTIONAL concurrency strategy uses JTA. Hence, it’s more suitable when entities are frequently modified.

Both READ_WRITE and TRANSACTIONAL use write-through caching, while NONSTRICT_READ_WRITE is a read-through caching strategy. For this reason, NONSTRICT_READ_WRITE is not very suitable if entities are changed frequently.

When using clustering, the second-level cache entries are spread across multiple nodes. When using Infinispan distributed cache, only READ_WRITE and NONSTRICT_READ_WRITE are available for read-write caches. Bear in mind that NONSTRICT_READ_WRITE offers a weaker consistency guarantee since stale updates are possible.

30. Credits

The full list of contributors to Hibernate ORM can be found on the GitHub repository.

The following contributors were involved in this documentation:

  • Gail Badner

  • Christian Bauer

  • Christian Beikov

  • Marco Belladelli

  • Emmanuel Bernard

  • Andrea Boriero

  • Chris Cranford

  • Steve Ebersole

  • Hardy Ferentschik

  • Sanne Grinovero

  • Louis Jacomet

  • Gavin King

  • Karel Maesen

  • Brett Meyer

  • Vlad Mihalcea

  • Gunnar Morling

  • Yoann Rodière

  • Max Rydahl Andersen

  • Jan Schatteman

  • Fábio Ueno

  • Radim Vansa

  • Nathan Xu

Appendix A: Configuration Settings

Configuration settings can be broadly broken down into 3 categories -

Jakarta Persistence

Settings which are standardized by the Jakarta Persistence specification for configuring any persistence provider. These settings are defined by the jakarta.persistence. namespace

Hibernate

Hibernate-specific settings which control various Hibernate behaviors which are extensions to or outside the scope of the Jakarta Persistence specification. These settings are defined by the hibernate. namespace

Legacy JPA

Settings which were standardized by Java Persistence, the legacy version of the Jakarta Persistence specification (prior to version 3.1). These settings are defined by the javax.persistence. namespace

For the time being, Hibernate continues to support the legacy Java Persistence settings in addition to the Jakarta Persistence forms. Applications should strongly consider migrating to the new Jakarta Persistence as support for the legacy Java Persistence will likely be removed at some point.

For (legacy) Hibernate settings which have a direct Jakarta Persistence corollary, the Jakarta Persistence form should be preferred - e.g. hibernate.connection.driver_classjakarta.persistence.jdbc.driver.

A.1. Jakarta Persistence Compliance Settings

hibernate.jpa.compliance

Since: 6.0

Default Value: true with JPA bootstrapping; false otherwise.

Specifies a default value for all JpaCompliance flags. Each individual flag may still be overridden by explicitly specifying its specific configuration property.


hibernate.jpa.compliance.caching

Since: 5.3

Default Value: JPA_COMPLIANCE

Hibernate’s default behavior here is safer and more careful than the behavior mandated by the TCK but YOLO

By default, Hibernate uses second-level cache invalidation for entities with secondary tables in order to avoid the possibility of inconsistent cached data in the case where different transactions simultaneously update different table rows corresponding to the same entity instance.

The Jakarta Persistence TCK, requires that entities with secondary tables be immediately cached in the second-level cache rather than invalidated and re-cached on a subsequent read.


hibernate.jpa.compliance.closed

Since: 5.3

Default Value: JPA_COMPLIANCE

When enabled, this setting forces Hibernate to throw an exception if close() is called on an instance that was already closed.

JPA specifies that an IllegalStateException must be thrown by EntityManager.close() and EntityManagerFactory.close() if the object has already been closed. By default, Hibernate treats any additional call to close() as a noop.


hibernate.jpa.compliance.global_id_generators

Since: 5.2.17

Default Value: JPA_COMPLIANCE

If enabled, the name will be considered globally scoped, and so the existence of two different generators with the same name will be considered a collision, and will result in an exception during bootstrap.

Determines whether the scope of any identifier generator name specified via TableGenerator.name() or SequenceGenerator.name() is considered global to the persistence unit, or local to the entity in which identifier generator is defined.


hibernate.jpa.compliance.list
This setting is considered deprecated

Since: 5.3

Default Value: JPA_COMPLIANCE

If enabled, Hibernate will recognize it as a list where the OrderColumn annotation is simply missing (and its defaults will apply).

Controls whether Hibernate should treat what it would usually consider a "bag", that is, a list with no index column, whose element order is not persistent, as a true list with an index column and a persistent element order.


hibernate.jpa.compliance.load_by_id

Since: 6.0

Default Value: JPA_COMPLIANCE

When enabled, coercion is disallowed, as required by the JPA specification. Hibernate’s default (here non-compliant) behavior is to allow the coercion.

Determines if an identifier value passed to EntityManager.find(java.lang.Class<T>, java.lang.Object) or EntityManager.getReference(java.lang.Class<T>, java.lang.Object) may be coerced to the identifier type declared by the entity. For example, an Integer argument might be widened to Long.


hibernate.jpa.compliance.orderby

Since: 6.0

Default Value: JPA_COMPLIANCE

If enabled, an exception is thrown for items which are not entity attribute references.

JPA specifies that items occurring in OrderBy lists must be references to entity attributes, whereas Hibernate, by default, allows more complex expressions.


hibernate.jpa.compliance.proxy

Since: 5.2.13

Default Value: JPA_COMPLIANCE

When enabled, this setting forces Hibernate to initialize the entity proxy when its identifier is accessed. Clearly, this setting is not recommended.

The JPA specification insists that an EntityNotFoundException must be thrown whenever an uninitialized entity proxy with no corresponding row in the database is accessed. For most programs, this results in many completely unnecessary round trips to the database.

Traditionally, Hibernate does not initialize an entity proxy when its identifier attribute is accessed, since the identifier value is already known and held in the proxy instance. This behavior saves the round trip to the database.


hibernate.jpa.compliance.query

Since: 5.3

Default Value: JPA_COMPLIANCE

When disabled, allows the many useful features of HQL

Controls whether Hibernate’s handling of Query (JPQL, Criteria and native) should strictly follow the requirements defined in the Jakarta Persistence specification, both in terms of JPQL validation and behavior of Query method implementations.


hibernate.jpa.compliance.transaction

When enabled, specifies that the Hibernate Transaction should behave according to the semantics defined by the JPA specification for an EntityTransaction.


A.2. Persistence Unit Settings

jakarta.persistence.provider

Specifies a class implementing PersistenceProvider. Naturally, this should always be HibernatePersistenceProvider, which is the best damn persistence provider ever. There’s no need to explicitly specify this setting when there are no inferior persistence providers floating about.

See JPA 2 sections 9.4.3 and 8.2.1.4


jakarta.persistence.transactionType

Specifies the type of transactions supported by the entity managers. The default depends on whether the program is considered to be executing in a Java SE or EE environment:

See JPA 2 sections 9.4.3 and 8.2.1.2


hibernate.archive.autodetection

Identifies a comma-separated list of values indicating the types of things we should auto-detect during scanning. Allowable values include:

  • "class" specifies that .class files are discovered as managed classes

  • "hbm" specifies that hbm.xml files are discovered as mapping files


hibernate.archive.interpreter

Specifies an ArchiveDescriptorFactory to use in the scanning process, either:

  • an instance of ArchiveDescriptorFactory,

  • a Class representing a class that implements ArchiveDescriptorFactory, or

  • the name of a class that implements ArchiveDescriptorFactory.

See information on Scanner about expected constructor forms.


hibernate.archive.scanner

Specifies an implementation of Scanner, either:

  • an instance of Scanner,

  • a Class representing a class that implements Scanner

  • the name of a class that implements Scanner.


hibernate.jpa_callbacks.enabled

Allows JPA callbacks (via PreUpdate and friends) to be completely disabled. Mostly useful to save some memory when they are not used.

JPA callbacks are enabled by default. Set this property to false to disable them.

Experimental and will likely be removed as soon as the memory overhead is resolved.


hibernate.persistenceUnitName

Specifies the name of the persistence unit.


hibernate.session_factory_name

Setting used to name the Hibernate SessionFactory.

Naming the SessionFactory allows for it to be properly serialized across JVMs as long as the same name is used on each JVM.

If SESSION_FACTORY_NAME_IS_JNDI is set to true, this is also the name under which the SessionFactory is bound into JNDI on startup and from which it can be obtained from JNDI.


hibernate.session_factory_name_is_jndi

Does the value defined by SESSION_FACTORY_NAME represent a JNDI namespace into which the SessionFactory should be bound and made accessible?

Defaults to true for backwards compatibility.

Set this to false if naming a SessionFactory is needed for serialization purposes, but no writable JNDI context exists in the runtime environment or if the user simply does not want JNDI to be used.


hibernate.session_factory_observer

Specifies a class which implements SessionFactoryObserver and has a constructor with no parameters.


javax.persistence.transactionType
This setting is considered deprecated

The type of transactions supported by the entity managers.

See JPA 2 sections 9.4.3 and 8.2.1.2


A.3. JDBC Settings

jakarta.persistence.database-major-version

Used in conjunction with "jakarta.persistence.database-product-name" for the purpose of determining the Dialect to use when the name does not provide enough detail.

The value is expected to match what would be returned from DatabaseMetaData.getDatabaseMajorVersion()) for the underlying database.


jakarta.persistence.database-minor-version

Used in conjunction with "jakarta.persistence.database-product-name" for the purpose of determining the Dialect to use when the name does not provide enough detail.

The value is expected to match what would be returned from DatabaseMetaData.getDatabaseMinorVersion()) for the underlying database.


jakarta.persistence.database-product-name

Specifies the name of the database vendor (as would be reported by DatabaseMetaData.getDatabaseProductName()) for the purpose of determining the Dialect to use.

For cases when the name of the database vendor is not enough alone, a combination of "jakarta.persistence.database-product-version", "jakarta.persistence.database-major-version" "jakarta.persistence.database-minor-version" can be used instead


jakarta.persistence.database-product-version

Used in conjunction with "jakarta.persistence.database-product-name" for the purpose of determining the Dialect to use when the name does not provide enough detail.

The value is expected to match what would be returned from DatabaseMetaData.getDatabaseProductVersion()) for the underlying database.


jakarta.persistence.jdbc.driver

Specifies the name of a JDBC driver to use to connect to the database.

Used in conjunction with JAKARTA_JDBC_URL, JAKARTA_JDBC_USER and JAKARTA_JDBC_PASSWORD to specify how to connect to the database.

When connections are obtained from a DataSource, use either JAKARTA_JTA_DATASOURCE or JAKARTA_NON_JTA_DATASOURCE instead.

See section 8.2.1.9


jakarta.persistence.jdbc.password

Specifies the password to use when connecting via JDBC.

Used in conjunction with JAKARTA_JDBC_DRIVER, JAKARTA_JDBC_URL and JAKARTA_JDBC_USER to specify how to connect to the database.

See JPA 2 section 8.2.1.9


jakarta.persistence.jdbc.url

Specifies the JDBC connection URL to use to connect to the database.

Used in conjunction with JAKARTA_JDBC_DRIVER, JAKARTA_JDBC_USER and JAKARTA_JDBC_PASSWORD to specify how to connect to the database.

When connections are obtained from a DataSource, use either JAKARTA_JTA_DATASOURCE or JAKARTA_NON_JTA_DATASOURCE instead.

See section 8.2.1.9


jakarta.persistence.jdbc.user

Specifies the database user to use when connecting via JDBC.

Used in conjunction with JAKARTA_JDBC_DRIVER, JAKARTA_JDBC_URL and JAKARTA_JDBC_PASSWORD to specify how to connect to the database.

Depending on the configured ConnectionProvider, the specified username might be used to:

See section 8.2.1.9


jakarta.persistence.jtaDataSource

Specifies a JTA DataSource to use for Connections. Hibernate allows either

See JPA 2 sections 9.4.3 and 8.2.1.5


jakarta.persistence.nonJtaDataSource

Specifies a non-JTA DataSource to use for Connections. Hibernate allows either

See JPA 2 sections 9.4.3 and 8.2.1.5


jakarta.persistence.schema-generation-connection

Allows passing a specific Connection instance to be used by SchemaManagementTool for the purpose of determining the Dialect, and for performing database actions if requested.


hibernate.connection

A prefix for properties specifying arbitrary JDBC connection properties. These properties are simply passed along to the provider when creating a connection.

For example, declaring hibernate.connection.foo=bar tells Hibernate to append foo=bar to the JDBC connection URL.


hibernate.connection.autocommit

Controls the autocommit mode of JDBC connections obtained from any ConnectionProvider implementation which respects this setting, which the built-in implementations do, except for DatasourceConnectionProviderImpl.


hibernate.connection.handling_mode

Specifies how Hibernate should manage JDBC connections in terms of acquisition and release, either:

The default is DELAYED_ACQUISITION_AND_RELEASE_AFTER_TRANSACTION.


hibernate.connection.isolation

Specified the JDBC transaction isolation level.


hibernate.connection.pool_size

Default Value: 20

Specifies the maximum number of inactive connections for the built-in connection pool.


hibernate.connection.provider_class

Specifies a ConnectionProvider to use for obtaining JDBC connections, either:

  • an instance of ConnectionProvider,

  • a Class representing a class that implements ConnectionProvider, or

  • the name of a class that implements ConnectionProvider.

The term "class" appears in the setting name due to legacy reasons; however it can accept instances.


hibernate.connection.provider_disables_autocommit

Since: 5.2.10

Default Value: false

By default, Hibernate calls Connection.setAutoCommit(boolean) on newly-obtained connections. This setting allows to circumvent that call (as well as other operations) in the interest of performance.

Indicates that Connections obtained from the configured ConnectionProvider have auto-commit already disabled when they are acquired.

It is inappropriate to set this value to true when the Connections returned by the provider do not, in fact, have auto-commit disabled. Doing so may lead to Hibernate executing SQL operations outside the scope of any transaction.


hibernate.dialect

As of Hibernate 6, this property should not be explicitly specified, except when using a custom user-written implementation of Dialect. Instead, applications should allow Hibernate to select the Dialect automatically.

Specifies the Hibernate SQL dialect, either

  • an instance of Dialect,

  • a Class representing a class that extends Dialect, or

  • the name of a class that extends Dialect.

By default, Hibernate will attempt to automatically determine the dialect from the JDBC URL and JDBC metadata, so this setting is not usually necessary.


hibernate.dialect.native_param_markers

Controls whether to use JDBC markers (?) or dialect native markers for parameters within preparable SQL statements.


hibernate.dialect_resolvers

Specifies additional DialectResolver implementations to register with the standard DialectFactory.


hibernate.format_sql

Default Value: false

Enables formatting of SQL logged to the console.


hibernate.highlight_sql

Default Value: false

Enables highlighting of SQL logged to the console using ANSI escape codes.


hibernate.jdbc.fetch_size

Default Value: 0

Gives the JDBC driver a hint as to the number of rows that should be fetched from the database when more rows are needed. If 0, the JDBC driver’s default settings will be used.


hibernate.jdbc.lob.non_contextual_creation

When enabled, specifies that Hibernate should not use contextual LOB creation.


hibernate.jdbc.log.warnings

When enabled, specifies that JDBC statement warnings should be logged.

The default is determined by Dialect.isJdbcLogWarningsEnabledByDefault().


hibernate.jdbc.time_zone

Since: 5.2.3

Specifies the time zone to use in the JDBC driver, which is supposed to match the database timezone.

The time zone may be given as:

By default, the JVM default time zone is assumed by the JDBC driver.


hibernate.jdbc.use_get_generated_keys

Specifies that generated primary keys may be retrieved using the JDBC 3 Statement.getGeneratedKeys() operation.

Usually, performance will be improved if this behavior is enabled, assuming the JDBC driver supports getGeneratedKeys().


hibernate.jdbc.use_scrollable_resultset

Default Value: true if the underlying driver supports scrollable results

Controls how Hibernate should handle scrollable results -

  • true indicates that insensitive scrolling can be used

  • false indicates that sensitive scrolling must be used


hibernate.log_slow_query

Specifies a duration in milliseconds defining the minimum query execution time that characterizes a "slow" query. Any SQL query which takes longer than this amount of time to execute will be logged.

A value of 0, the default, disables logging of "slow" queries.


hibernate.session_factory.statement_inspector

Specifies a StatementInspector implementation associated with the SessionFactory, either:

  • an instance of StatementInspector,

  • a Class representing an class that implements StatementInspector, or

  • the name of a class that implements StatementInspector.


hibernate.show_sql

Default Value: false

Enables logging of generated SQL to the console.


hibernate.use_sql_comments

Default Value: false

Specifies that comments should be added to the generated SQL.


A.4. C3P0 Connection Pool Settings

hibernate.c3p0

A setting prefix used to indicate settings that target the hibernate-c3p0 integration


hibernate.c3p0.acquire_increment

Number of connections acquired when pool is exhausted


hibernate.c3p0.idle_test_period

Idle time before a C3P0 pooled connection is validated


hibernate.c3p0.max_size

Maximum size of C3P0 connection pool


hibernate.c3p0.max_statements

Maximum size of C3P0 statement cache


hibernate.c3p0.min_size

Minimum size of C3P0 connection pool


hibernate.c3p0.timeout

Maximum idle time for C3P0 connection pool


A.5. Proxool Connection Pool Settings

hibernate.proxool

A setting prefix used to indicate settings that target the hibernate-proxool integration


hibernate.proxool.existing_pool

Proxool property to configure the Proxool Provider from an already existing pool (true / false)


hibernate.proxool.pool_alias

Proxool property with the Proxool pool alias to use (Required for PROXOOL_EXISTING_POOL, PROXOOL_PROPERTIES, or PROXOOL_XML)


hibernate.proxool.properties

Proxool property to configure the Proxool provider using a properties file (/path/to/proxool.properties)


hibernate.proxool.xml

Proxool property to configure the Proxool provider using an XML (/path/to/file.xml)


A.6. Proxool Connection Pool Settings

hibernate.allow_update_outside_transaction

When enabled, allows update operations outside a transaction.

Since version 5.2 Hibernate conforms with the JPA specification and disallows flushing any update outside a transaction.

Values are true, which allows flushing outside a transaction, and false, which does not.

The default behavior is to disallow update operations outside a transaction.


hibernate.enable_lazy_load_no_trans

Default Value: false (disabled)

Allows a detached proxy or lazy collection to be fetched even when not associated with an open persistence context, by creating a temporary persistence context when the proxy or collection is accessed. This behavior is not recommended, since it can easily break transaction isolation or lead to data aliasing; it is therefore disabled by default.


hibernate.jta.allowTransactionAccess

Default Value: false when bootstrapped via JPA; true otherwise.

When enabled, allows access to the Transaction even when using a JTA for transaction management.

Values are true, which grants access, and false, which does not.


hibernate.jta.cacheTransactionManager

Since: 4.0

Default Value: Generally true, though JtaPlatform implementations can do their own thing.

When enabled, indicates that it is safe to cache TransactionManager references in the JtaPlatform


hibernate.jta.cacheUserTransaction

Since: 4.0

Default Value: Generally true, though JtaPlatform implementations can do their own thing.

When enabled, indicates that it is safe to cache UserTransaction references in the JtaPlatform


hibernate.jta.prefer_user_transaction

Since: 5.0

Default Value: false as TransactionManager is preferred.

When enabled, specifies that the UserTransaction should be used in preference to the TransactionManager for JTA transaction management.

By default, the TransactionManager is preferred.


hibernate.jta.track_by_thread

Default Value: true (enabled).

A transaction can be rolled back by another thread ("tracking by thread") — not the original application. Examples of this include a JTA transaction timeout handled by a background reaper thread. The ability to handle this situation requires checking the Thread ID every time Session is called. This can certainly have performance considerations.


hibernate.transaction.auto_close_session

Default Value: false

When enabled, specifies that the Session should be closed automatically at the end of each transaction.


hibernate.transaction.coordinator_class

Since: 5.0

Default Value: With Jakarta Persistence bootstrapping, based on the persistence unit’s PersistenceUnitInfo.getTransactionType(); otherwise jdbc.

Specify the TransactionCoordinatorBuilder implementation to use for creating instances of TransactionCoordinator which the interface Hibernate uses to manage transactions.

Accepts either:
  • an instance of TransactionCoordinatorBuilder,

  • a Class representing a class that implements TransactionCoordinatorBuilder,

  • the name of a class that implements TransactionCoordinatorBuilder,

  • jta or jdbc


hibernate.transaction.flush_before_completion

Default Value: true unless using JPA bootstrap

When enabled, specifies that automatic flushing should occur during the JTA Synchronization.beforeCompletion() callback.


hibernate.transaction.jta.platform

Specifies the JtaPlatform implementation to use for integrating with JTA, either:

  • an instance of JtaPlatform, or

  • the name of a class that implements JtaPlatform.

  • short name of a class (sans package name) that implements JtaPlatform.


hibernate.transaction.jta.platform_resolver

Specifies a JtaPlatformResolver implementation that should be used to obtain an instance of JtaPlatform.


A.7. Domain Mapping Settings

hibernate.auto_quote_keyword

Since: 5.0

Default Value: false - auto-quoting of SQL keywords is disabled by default.

Specifies whether to automatically quote any names that are deemed keywords on the underlying database.


hibernate.column_ordering_strategy

Since: 6.2

Default Value: "default"

Used to specify the ColumnOrderingStrategy class to use. The following shortcut names are defined for this setting:


hibernate.create_empty_composites.enabled
This setting is considered deprecated

Since: 5.1

This is an experimental feature that has known issues. It should not be used in production until it is stabilized. See Hibernate JIRA issue HHH-11936 for details.

Enable instantiation of composite/embedded objects when all attribute values are null. The default (and historical) behavior is that a null reference will be used to represent the composite value when all of its attributes are null.


hibernate.default_catalog

A default database catalog name to use for unqualified database object (table, sequence, …​) names


hibernate.default_schema

A default database schema (owner) name to use for unqualified database object (table, sequence, …​) names


hibernate.discriminator.ignore_explicit_for_joined

Controls whether Hibernate should ignore explicit discriminator metadata with joined inheritance.

Hibernate does not need a discriminator with joined inheritance. Historically it simply ignored discriminator metadata. When enabled (true), any discriminator metadata (DiscriminatorColumn, e.g.) is ignored allowing for backwards compatibility.


hibernate.discriminator.implicit_for_joined

Controls whether Hibernate should infer a discriminator for entity hierarchies defined with joined inheritance.

Hibernate does not need a discriminator with joined inheritance. Therefore, its legacy behavior is to not infer a discriminator. However, some JPA providers do require discriminators with joined inheritance, so in the interest of portability this option has been added to Hibernate. When enabled (true), Hibernate will treat the absence of discriminator metadata as an indication to use the JPA defined defaults for discriminators.


hibernate.globally_quoted_identifiers

When enabled, all database identifiers are quoted.

Corollary to the JPA <delimited-identifiers/> element within the orm.xml <persistence-unit-defaults/> element, but offered as a global flag.


hibernate.globally_quoted_identifiers_skip_column_definitions

Default Value: false to avoid the potential problems quoting non-trivial column-definitions.

Controls whether column-definitions (Column.columnDefinition(), JoinColumn.columnDefinition(), etc.) should be auto-quoted as part of global quoting.

When global quoting is enabled, JPA states that column-definitions are subject to quoting. However, this can lead to problems with definitions such as @Column(…​, columnDefinition="INTEGER DEFAULT 20").


hibernate.id.db_structure_naming_strategy

An implicit naming strategy for database structures (tables, sequences) related to identifier generators.

Resolution uses the StrategySelector service and accepts any of the forms discussed on StrategySelector.resolveDefaultableStrategy(Class, Object, java.util.concurrent.Callable).

The recognized short names being:


hibernate.id.generator.stored_last_used

Since: 5.3

Default Value: The value stored in the database table is the last generated value

Determines if the identifier value stored in the database table backing a table generator is the last value returned by the identifier generator, or the next value to be returned.


hibernate.id.optimizer.pooled.preferred

When a generator specifies an increment-size and an optimizer was not explicitly specified, which of the "pooled" optimizers should be preferred? Can specify an optimizer short name or the name of a class which implements Optimizer.


hibernate.id.sequence.increment_size_mismatch_strategy

Since: 5.4

Default Value: SequenceMismatchStrategy.EXCEPTION, meaning that an exception is thrown when such a conflict is detected.

This setting defines the SequenceMismatchStrategy used when Hibernate detects a mismatch between a sequence configuration in an entity mapping and its database sequence object counterpart.


hibernate.implicit_naming_strategy

Since: 5.0

Default Value: "default"

Used to specify the ImplicitNamingStrategy class to use. The following shortcut names are defined for this setting:


hibernate.jpa.metamodel.population

Setting that indicates whether to build the JPA types, either:

  • enabled - Do the build

  • disabled - Do not do the build

  • ignoreUnsupported - Do the build, but ignore any non-JPA features that would otherwise result in a failure.


hibernate.jpa.static_metamodel.population

Setting that controls whether we seek out JPA "static metamodel" classes and populate them, either:

  • enabled - Do the population

  • disabled - Do not do the population

  • skipUnsupported - Do the population, but ignore any non-JPA features that would otherwise result in the population failing.


hibernate.mapping.default_list_semantics

Specifies the CollectionClassification to use for a plural attribute typed as List with no explicit list index details (OrderColumn, ListIndexBase, etc.).

Accepts any of:

  • an instance of CollectionClassification

  • the (case insensitive) name of a CollectionClassification (list e.g.)

  • a Class representing either List or Collection


hibernate.mapping.precedence
This setting is considered deprecated

Default Value: "hbm,class", which indicates that hbm.xml files should be processed first, followed by annotations and orm.xml files.

Specifies the order in which metadata sources should be processed, is a delimited list of values defined by MetadataSourceType.


hibernate.physical_naming_strategy

Since: 5.0

Default Value: PhysicalNamingStrategyStandardImpl, in which case physical names are taken to be identical to logical names.

Specifies the PhysicalNamingStrategy to use.


hibernate.timezone.default_storage

Since: 6.0

Default Value: DEFAULT, which guarantees that the instant represented by a zoned datetime type is preserved by a round trip to the database. It does not guarantee that the time zone or offset is preserved.

For backward compatibility with older versions of Hibernate, set this property to NORMALIZE.

Specifies the default strategy for storage of the timezone information for the zoned datetime types OffsetDateTime and ZonedDateTime. The possible options for this setting are enumerated by TimeZoneStorageType.


hibernate.transform_hbm_xml.enabled

Since: 6.1

Default Value: false (opt-in).

Enables processing hbm.xml mappings by transforming them to mapping.xml and using that processor.


hibernate.transform_hbm_xml.unsupported_feature_handling

How features in a hbm.xml file which are not supported for transformation should be handled. Valid values are defined by UnsupportedFeatureHandling


hibernate.type.json_format_mapper

Specifies a FormatMapper used for JSON serialization and deserialization, either:

  • an instance of FormatMapper,

  • a Class representing a class that implements FormatMapper,

  • the name of a class that implements FormatMapper, or

  • one of the shorthand constants jackson or jsonb.

By default, the first of the possible providers that is available at runtime is used, according to the listing order.


hibernate.type.preferred_boolean_jdbc_type

Specifies the preferred JDBC type for storing boolean values.

Can be overridden locally using JdbcType, JdbcTypeCode, and friends.

Can also specify the name of the SqlTypes constant field, for example, hibernate.type.preferred_boolean_jdbc_type=BIT.


hibernate.type.preferred_duration_jdbc_type

The preferred JDBC type to use for storing Duration values.

Can be overridden locally using JdbcType, JdbcTypeCode, and friends.

Can also specify the name of the SqlTypes constant field, for example, hibernate.type.preferred_duration_jdbc_type=INTERVAL_SECOND.


hibernate.type.preferred_instant_jdbc_type

Specifies the preferred JDBC type for storing Instant values.

Can be overridden locally using JdbcType, JdbcTypeCode, and friends.

Can also specify the name of the SqlTypes constant field, for example, hibernate.type.preferred_instant_jdbc_type=TIMESTAMP.


hibernate.type.preferred_uuid_jdbc_type

The preferred JDBC type to use for storing UUID values.

Can be overridden locally using JdbcType, JdbcTypeCode, and friends.

Can also specify the name of the SqlTypes constant field, for example, hibernate.type.preferred_uuid_jdbc_type=CHAR.


hibernate.type.wrapper_array_handling

Configurable control over how to handle Byte[] and Character[] types encountered in the application domain model. Allowable semantics are defined by WrapperArrayHandling. Accepted values include:


hibernate.type.xml_format_mapper

Specifies a FormatMapper used for XML serialization and deserialization, either:

  • an instance of FormatMapper,

  • a Class representing a class that implements FormatMapper,

  • the name of a class that implements FormatMapper, or

  • one of the shorthand constants jackson or jaxb.

By default, the first of the possible providers that is available at runtime is used, according to the listing order.


hibernate.use_entity_where_clause_for_collections
This setting is considered deprecated

The setting is very misnamed - it applies across all entity associations, not only to collections.

The @Where annotation specifies a restriction on the table rows which are visible as entity class instances or collection elements.

This setting controls whether the restriction applied to an entity should be applied to association fetches (for one-to-one, many-to-one, one-to-many, and many-to-many associations) which target the entity.


hibernate.use_nationalized_character_data

Default Value: false (disabled)

This is a global setting applying to all mappings associated with a given SessionFactory. The Nationalized annotation may be used to selectively enable nationalized character support for specific columns.

By default, Hibernate maps character data represented by Strings and Clobs to the JDBC types Types.VARCHAR and Types.CLOB. This setting, when enabled, turns on the use of explicit nationalized character support for mappings involving character data, specifying that the JDBC types Types.NVARCHAR and Types.NCLOB should be used instead.

This setting is relevant for use with databases with explicit nationalization support, and it is not needed for databases whose native varchar and clob types support Unicode data. (If you’re not sure how your database handles Unicode, check out the implementation of Dialect.getNationalizationSupport() for its SQL dialect.)

Enabling this setting has two effects:


hibernate.validate_xml

Since: 6.1

Default Value: true

Whether XML should be validated against their schema as Hibernate reads them.


hibernate.xml_mapping_enabled

Since: 5.4.1

Default Value: true - XML mappings are processed

This is a performance optimization appropriate when mapping details are defined exclusively using annotations.

Whether XML mappings should be processed.


A.8. Fetch Related Settings

hibernate.batch_fetch_style
This setting is considered deprecated

Specifies the BatchFetchStyle to use, either the name of a {code BatchFetchStyle} instance, or an instance of BatchFetchStyle.


hibernate.default_batch_fetch_size

Specifies the default value for batch fetching.

By default, Hibernate only uses batch fetching for entities and collections explicitly annotated `@BatchSize`.

hibernate.max_fetch_depth

Default Value: 0 (none)

Specifies the maximum depth of nested outer join fetching.


hibernate.use_subselect_fetch

When enabled, Hibernate will use subselect fetching, when possible, to fetch any collection. Subselect fetching involves fetching the collection based on the restriction used to load it owner(s).

By default, Hibernate only uses subselect fetching for collections explicitly annotated @Fetch(SUBSELECT).


A.9. JDBC Batch Settings

hibernate.jdbc.batch.builder

Default Value: Standard builder based on STATEMENT_BATCH_SIZE

Names the BatchBuilder implementation to use.


hibernate.jdbc.batch_size

Default Value: 0

Specifies the maximum number of statements to batch together.

A nonzero value enables batching

hibernate.jdbc.batch_versioned_data

Default Value: Generally true, though can vary based on Dialect

When enabled, specifies that versioned data should be included in batching.


hibernate.order_inserts

Default Value: false

Enable ordering of insert statements by primary key value, for the purpose of more efficient JDBC batching.


hibernate.order_updates

Default Value: false

Enable ordering of update statements by primary key value, for the purpose of more efficient JDBC batching


A.10. Bytecode Manipulation Settings

hibernate.bytecode.provider
This setting is considered deprecated

Default Value: "bytebuddy"

Selects a bytecode enhancement library.

At present only bytebuddy is supported, bytebuddy being the default since version 5.3.


hibernate.enhancer.enableAssociationManagement

Enable association management feature in runtime bytecode enhancement


A.11. Second-level Cache Settings

jakarta.persistence.cache.retrieveMode

Set a default value for SpecHints.HINT_SPEC_CACHE_RETRIEVE_MODE, used when the hint is not explicitly specified.

It does not usually make sense to change the default from CacheRetrieveMode.USE.


jakarta.persistence.cache.storeMode

Set a default value for SpecHints.HINT_SPEC_CACHE_STORE_MODE, used when the hint is not explicitly specified.

It does not usually make sense to change the default from CacheStoreMode.USE.


jakarta.persistence.sharedCache.mode

When enabled, specifies that the second-level cache (which JPA calls the "shared" cache) may be used, as per the rules defined in JPA 2 section 3.1.7.

See JPA 2 sections 9.4.3 and 8.2.1.7


hibernate.cache.auto_evict_collection_cache

Default Value: false

Enables the automatic eviction of a bidirectional association’s collection cache when an element in the ManyToOne collection is added, updated, or removed without properly managing the change on the OneToMany side.


hibernate.cache.default_cache_concurrency_strategy

Default Value: The cache provider’s default strategy

Specifies the CacheConcurrencyStrategy to use by default when an entity is marked @Cacheable, but no concurrency strategy is explicitly specified via the Cache annotation.

An explicit strategy may be specified using @Cache(usage=…​).


hibernate.cache.keys_factory
This setting is considered deprecated

Since: 5.2

Specifies the CacheKeysFactory to use, either:


hibernate.cache.query_cache_factory

Specifies the TimestampsCacheFactory to use.


hibernate.cache.region.factory_class

The RegionFactory implementation, either:

Defaults to NoCachingRegionFactory, so that caching is disabled.


hibernate.cache.region_prefix

The CacheProvider region name prefix


hibernate.cache.use_minimal_puts

Default Value: The cache provider’s default

Optimize interaction with the second-level cache to minimize writes, at the cost of an additional read before each write. This setting is useful if writes to the cache are much more expensive than reads from the cache, for example, if the cache is a distributed cache.

It’s not usually necessary to set this explicitly because, by default, it’s set to a sensible value by the second-level cache implementation.


hibernate.cache.use_query_cache

Default Value: false

Enable the query results cache


hibernate.cache.use_reference_entries

Enable direct storage of entity references into the second level cache when applicable. This is appropriate only for immutable entities.

By default, entities are always stored in a "disassembled" form, that is, as a tuple of attribute values.


hibernate.cache.use_second_level_cache

Default Value: true when a provider is specified; false otherwise.

When enabled, specifies that the second-level cache may be used.

By default, if the configured RegionFactory is not the NoCachingRegionFactory, then the second-level cache is enabled. Otherwise, the second-level cache is disabled.


hibernate.cache.use_structured_entries

Default Value: false

Enables the use of structured second-level cache entries. This makes the cache entries human-readable, but carries a performance cost.


hibernate.classcache

Entity cache configuration properties follow the pattern hibernate.classcache.packagename.ClassName usage[, region] where usage is the cache strategy used and region the cache region name


hibernate.collectioncache

Collection cache configuration properties follow the pattern hibernate.collectioncache.packagename.ClassName.role usage[, region] where usage is the cache strategy used and region the cache region name


hibernate.javax.cache.cache_manager

Allows providing hibernate-jcache with a custom JCache CacheManager.


hibernate.javax.cache.missing_cache_strategy

Define the behavior of the region factory when a cache is missing, i.e. when the cache was not created by the cache manager as it started. See MissingCacheStrategy for the various possible values. Default value is MissingCacheStrategy.FAIL.


hibernate.javax.cache.provider

Allows providing hibernate-jcache with a custom JCache CachingProvider.


hibernate.javax.cache.uri

Designates the URI for a specific JCache CacheManager JCacheRegionFactory should ask the CachingProvider for


javax.persistence.sharedCache.mode
This setting is considered deprecated

Used to indicate whether second-level (what JPA terms shared cache) caching is enabled as per the rules defined in JPA 2 section 3.1.7.

See JPA 2 sections 9.4.3 and 8.2.1.7


A.12. CDI Settings

jakarta.persistence.bean.manager

Used to pass a CDI BeanManager to Hibernate.

According to the JPA specification, the BeanManager should be passed at boot time and be ready for immediate use at that time. But not all environments can do this (WildFly, for example). To accommodate such environments, Hibernate provides two options:

  • A proprietary CDI extension SPI (which has been proposed to the CDI spec group as a standard option) which can be used to provide delayed BeanManager access: to use this solution, the reference passed as the BeanManager during bootstrap should be typed as ExtendedBeanManager.

  • Delayed access to the BeanManager reference: here, Hibernate will not access the reference passed as the BeanManager during bootstrap until it is first needed. Note, however, that this has the effect of delaying the detection of any deployment problems until after bootstrapping. This setting is used to configure access to the BeanManager, either directly, or via ExtendedBeanManager.


hibernate.cdi.extensions

Controls whether Hibernate can try to create beans other than converters and listeners using CDI. Only meaningful when a CDI container is used.

By default, Hibernate will only attempt to create converter and listener beans using CDI.


hibernate.delay_cdi_access

Used in conjunction with "hibernate.resource.beans.container" when CDI is used.

By default, to be JPA spec compliant, Hibernate should access the CDI BeanManager while bootstrapping the SessionFactory. In some cases however this can lead to a chicken/egg situation where the JPA provider immediately accesses the BeanManager when managed beans are awaiting JPA PU injection.

This setting tells Hibernate to delay accessing until first use.

This setting has the decided downside that bean config problems will not be done at deployment time, but will instead manifest at runtime. For this reason, the preferred means for supplying a CDI BeanManager is to provide an implementation of ExtendedBeanManager which gives Hibernate a callback when the BeanManager is ready for use.


hibernate.resource.beans.container

Identifies a BeanContainer to be used.

Note that for CDI-based containers setting this is not necessary - simply pass the BeanManager to use via CDI_BEAN_MANAGER and optionally specify DELAY_CDI_ACCESS. This setting useful to integrate non-CDI bean containers such as Spring.


A.13. Dialect Specific Settings

hibernate.dialect.cockroach.version_string

Specifies a custom CockroachDB version string. The expected format of the string is the one returned from the version() function, e.g.: "CockroachDB CCL v23.1.8 (x86_64-pc-linux-gnu, built 2023/08/04 18:11:44, go1.19.10)"


hibernate.dialect.mysql.bytes_per_character

Specifies the bytes per character to use based on the database’s configured charset.


hibernate.dialect.mysql.no_backslash_escapes

Specifies whether the NO_BACKSLASH_ESCAPES sql mode is enabled.


hibernate.dialect.oracle.extended_string_size

Specifies whether this database’s MAX_STRING_SIZE is set to EXTENDED.


hibernate.dialect.oracle.is_autonomous

Specifies whether this database is running on an Autonomous Database Cloud Service.


hibernate.dialect.sybase.extended_string_size

Default Value: false

Specifies whether this database’s ansinull setting is enabled.


A.14. Audit/History Settings

org.hibernate.envers.allow_identifier_reuse

Guarantees proper validity audit strategy behavior when application reuses identifiers of deleted entities. Exactly one row with null end date exists for each identifier.


org.hibernate.envers.audit_strategy

Audit strategy. Defaults to DefaultAuditStrategy.


org.hibernate.envers.audit_strategy_validity_end_rev_field_name

Column name that will hold the end revision number in audit entities. Defaults to REVEND.


org.hibernate.envers.audit_strategy_validity_revend_timestamp_field_name

Column name of the timestamp of the end revision until which the data was valid. Defaults to REVEND_TSTMP.


org.hibernate.envers.audit_strategy_validity_revend_timestamp_legacy_placement

Whether to use legacy validity audit strategy revision end timestamp behavior where the field is not included as part of the joined entity inheritance subclass audit tables. Defaults to true.


org.hibernate.envers.audit_strategy_validity_revend_timestamp_numeric

Determines whether the timestamp of the end revision is stored as a numeric data type. Defaults to false.


org.hibernate.envers.audit_strategy_validity_store_revend_timestamp

Store the timestamp of the end revision, until which the data was valid, in addition to the end revision itself. Defaults to false.


org.hibernate.envers.audit_table_prefix

Audit table prefix. Empty by default.


org.hibernate.envers.audit_table_suffix

Audit table suffix. Defaults to _AUD.


org.hibernate.envers.cascade_delete_revision

Deletion of a revision entity will cause a foreign key constraint database error when at least one audit record exists for that revision. By enabling this feature, deletion of the revision entity will also force all audit records associated to that revision to be deleted via cascade. Defaults to false.


org.hibernate.envers.default_catalog

Default name of the catalog containing audit tables.


org.hibernate.envers.default_schema

Default name of the schema containing audit tables.


org.hibernate.envers.do_not_audit_optimistic_locking_field

Treats optimistic locking properties as unversioned. Defaults to true.


org.hibernate.envers.embeddable_set_ordinal_field_name

Name of column used for storing ordinal of the change in sets of embeddable elements. Defaults to SETORDINAL.


org.hibernate.envers.find_by_revision_exact_match

Forces AuditReader#find implementations that accept a revision-number argument to perform an exact match against the supplied revision number rather than potentially returning hits that are less-than or equal-to the supplied revision number. This option is meant to maintain backward compatibility while attempting to correct a bug in behavior without impacting existing users who may use the current behavior. Defaults to false.


org.hibernate.envers.global_relation_not_found_legacy_flag

Globally defines whether legacy relation not-found behavior should be used or not. Defaults to true. By specifying true, any EntityNotFoundException will be thrown unless the containing class or property explicitly specifies that use case to be ignored. Conversely, when specifying the value false, the inverse applies and requires explicitly specifying the use case as error so that the exception is thrown.


org.hibernate.envers.global_with_modified_flag

Globally activates modified properties flag feature. Defaults to false.


org.hibernate.envers.modified_column_naming_strategy

org.hibernate.envers.modified_flag_suffix

Suffix of modified flag columns. Defaults to _MOD.


org.hibernate.envers.original_id_prop_name

Original id property name name. Defaults to originalId.


org.hibernate.envers.revision_field_name

Revision field name. Defaults to REV.


org.hibernate.envers.revision_listener

Fully qualified class name of user defined revision listener.


org.hibernate.envers.revision_on_collection_change

Triggers revision generation when not-owned relation field changes. Defaults to true.


org.hibernate.envers.revision_sequence_nocache

Whether to apply a nocache configuration for the revision sequence. This is mostly interesting for testing.


org.hibernate.envers.revision_type_field_name

Revision type field name. Defaults to REVTYPE.


org.hibernate.envers.store_data_at_delete

Indicates whether entity data should be stored during removal. Defaults to false.


org.hibernate.envers.track_entities_changed_in_revision

Track entity names that have been changed during each revision. Defaults to false.


org.hibernate.envers.use_revision_entity_with_native_id

Use revision entity with native identifier generator. Defaults to true for backward compatibility.


A.15. Runtime Environment Settings

hibernate.classLoader.tccl_lookup_precedence

Specifies how the thread context class loader must be used for class lookup.


hibernate.classLoaders

Specifies a collection of the ClassLoader instances Hibernate should use for classloading and resource loading.


hibernate.jndi

A prefix for properties specifying arbitrary JNDI InitialContext properties. These properties are simply passed along to the constructor InitialContext(java.util.Hashtable).


hibernate.jndi.class

Specifies the JNDI InitialContextFactory implementation class to use. Passed along to InitialContext(Hashtable) as "java.naming.factory.initial".


hibernate.jndi.url

Specifies the JNDI provider/connection URL. Passed along to InitialContext(Hashtable) as "java.naming.provider.url".


A.16. Miscellaneous Settings

jakarta.persistence.lock.scope

Set a default value for the hint SpecHints.HINT_SPEC_LOCK_SCOPE, used when the hint is not explicitly specified.

See JPA 2 sections 8.2.1.9 and 3.4.4.3


jakarta.persistence.lock.timeout

Set a default value for the hint SpecHints.HINT_SPEC_LOCK_TIMEOUT, used when the hint is not explicitly specified.

See JPA 2 sections 8.2.1.9 and 3.4.4.3


hibernate.allow_refresh_detached_entity

When enabled, allows calls to EntityManager.refresh(Object) and Session.refresh(Object) on a detached entity instance.

Values are true, which allows refreshing a detached instance and false, which does not. When refreshing is disallowed, an IllegalArgumentException is thrown.

The default behavior is to allow refreshing a detached instance unless Hibernate is bootstrapped via JPA.


hibernate.current_session_context_class

Specifies a CurrentSessionContext for scoping the current session, either:

  • jta, thread, or managed, or

  • the name of a class implementing org.hibernate.context.spi.CurrentSessionContext. If this property is not set, but JTA support is enabled, then JTASessionContext is used by default.


hibernate.discard_pc_on_close

Default Value: false (not discarded) per the JPA specification.

When enabled, specifies that the persistent context should be discarded when either SharedSessionContract.close() or EntityManager.close() is called.


hibernate.entity_dirtiness_strategy

Setting to identify a CustomEntityDirtinessStrategy to use. May specify either a class name or an instance.


hibernate.event.listener

Event listener configuration properties follow the pattern hibernate.event.listener.eventType packageName.ClassName1, packageName.ClassName2


hibernate.event.merge.entity_copy_observer

Setting that specifies how Hibernate will respond when multiple representations of the same persistent entity ("entity copy") are detected while merging.

The possible values are:

  • disallow (the default): throws IllegalStateException if an entity copy is detected

  • allow: performs the merge operation on each entity copy that is detected

  • log: (provided for testing only) performs the merge operation on each entity copy that is detected and logs information about the entity copies. This setting requires DEBUG logging be enabled for EntityCopyAllowedLoggedObserver.

Alternatively, the application may customize the behavior by providing an implementation of EntityCopyObserver and setting the property "hibernate.event.merge.entity_copy_observer" to the class name.

When this property is set to allow or log, Hibernate will merge each entity copy detected while cascading the merge operation. In the process of merging each entity copy, Hibernate will cascade the merge operation from each entity copy to its associations with CascadeType.MERGE or CascadeType.ALL. The entity state resulting from merging an entity copy will be overwritten when another entity copy is merged.


hibernate.identifier_generator_strategy_provider
This setting is considered deprecated

Specifies a class which implements IdentifierGeneratorStrategyProvider, and has a constructor with no parameters.


hibernate.loader.delay_entity_loader_creations

Controls how entity loaders are created.

When true, the default, the loaders are only created on first access; this ensures that all access patterns which are not useful to the application are never instantiated, possibly saving a substantial amount of memory for applications having many entities. The only exception is the loader for LockMode.NONE, which will always be eagerly initialized; this is necessary to detect mapping errors.

false indicates that all loaders should be created up front; this will consume more memory but ensures all necessary memory is allocated right away.


hibernate.use_identifier_rollback

Default Value: false - generated identifiers are not unset

When enabled, specifies that the generated identifier of an entity is unset when the entity is deleted.


A.17. Query Settings

hibernate.criteria.copy_tree

When enabled, specifies that queries created via EntityManager.createQuery(CriteriaQuery), EntityManager.createQuery(CriteriaUpdate) or EntityManager.createQuery(CriteriaDelete) must create a copy of the passed criteria query object such that the resulting Query object is not affected by mutation of the original criteria query.

If disabled, it’s assumed that the client does not mutate the criteria query after calling createQuery(). Thus, in the interest of performance, no copy is created.

The default behavior depends on how Hibernate is bootstrapped:

  • When bootstrapping Hibernate through the native bootstrap APIs, this setting is disabled, that is, no copy of the criteria query object is made.

  • When bootstrapping Hibernate through the JPA SPI, this setting is enabled so that criteria query objects are copied, as required by the JPA specification.


hibernate.criteria.value_handling_mode

By default, a criteria query produces SQL with a JDBC bind parameter for any value specified via the criteria query API, except when the value is passed via CriteriaBuilder.literal(Object), in which case the value is "inlined" as a SQL literal.

This setting may be used to override this default behavior:

  • the "bind" mode uses bind parameters to pass such values to JDBC, but

  • the "inline" mode inlines values as SQL literals.

In both modes:

The default mode is ValueHandlingMode.BIND.


hibernate.order_by.default_null_ordering

Specifies the default precedence of null values in the HQL ORDER BY clause, either none, first, or last.

The default is none.


hibernate.query.fail_on_pagination_over_collection_fetch

When pagination is used in combination with a fetch join applied to a collection or many-valued association, the limit must be applied in-memory instead of on the database. This typically has terrible performance characteristics, and should be avoided.

When enabled, this setting specifies that an exception should be thrown for any query which would result in the limit being applied in-memory.

By default, the exception is disabled, and the possibility of terrible performance is left as a problem for the client to avoid.


hibernate.query.hql.translator

Specifies a HqlTranslator to use for HQL query translation.


hibernate.query.immutable_entity_update_query_handling_mode

This setting defines how Immutable entities are handled when executing a bulk update query. Valid options are enumerated by ImmutableEntityUpdateQueryHandlingMode:

By default, a warning is logged.


hibernate.query.in_clause_parameter_padding

Determines how parameters occurring in a SQL IN predicate are expanded. By default, the IN predicate expands to include sufficient bind parameters to accommodate the specified arguments.

However, for database systems supporting execution plan caching, there’s a better chance of hitting the cache if the number of possible IN clause parameter list lengths is smaller.

When this setting is enabled, we expand the number of bind parameters to an integer power of two: 4, 8, 16, 32, 64. Thus, if 5, 6, or 7 arguments are bound to a parameter, a SQL statement with 8 bind parameters in the IN clause will be used, and null will be bound to the left-over parameters.


hibernate.query.insert_strategy

Defines the "global" strategy to use for handling HQL and Criteria insert queries. Specifies a SqmMultiTableInsertStrategy.


hibernate.query.mutation_strategy

Defines the "global" strategy to use for handling HQL and Criteria mutation queries. Specifies a SqmMultiTableMutationStrategy..


hibernate.query.native.ignore_jdbc_parameters

When set to true, indicates that ordinal parameters (represented by the '?' placeholder) in native queries will be ignored.

By default, this is set to false, i.e. native queries will be checked for ordinal placeholders.


hibernate.query.plan_cache_enabled

When enabled, specifies that query plans should be cached.

By default, the query plan cache is disabled, unless one of the configuration properties "hibernate.query.plan_cache_max_size" or "hibernate.query.plan_parameter_metadata_max_size" is set.


hibernate.query.plan_cache_max_size

The maximum number of entries in the query interpretation cache.

The default maximum is 2048.


hibernate.query.plan_parameter_metadata_max_size
This setting is considered deprecated

The maximum number of ParameterMetadata instances maintained by the QueryInterpretationCache.


hibernate.query.proc.callable_named_params_enabled

When enabled, specifies that Hibernate should attempt to map parameter names given in a ProcedureCall or StoredProcedureQuery to named parameters of the JDBC CallableStatement.


hibernate.query.sqm.translator

Specifies a SqmTranslatorFactory to use for HQL query translation.


hibernate.query.startup_check

When enabled, specifies that named queries be checked during startup.

By default, named queries are checked at startup.

Mainly intended for use in test environments.


A.18. Schema Tooling Settings

jakarta.persistence.create-database-schemas

The JPA variant of HBM2DDL_CREATE_NAMESPACES used to specify whether database schemas used in the mapping model should be created on export in addition to creating the tables, sequences, etc.

The default is false, meaning to not create schemas


jakarta.persistence.schema-generation.create-script-source

Specifies the CREATE script file as either a Reader configured for reading the DDL script file or a string designating a file URL for the DDL script.

Hibernate historically also accepted HBM2DDL_IMPORT_FILES for a similar purpose. This setting is now preferred.


jakarta.persistence.schema-generation.create-source

Specifies whether schema generation commands for schema creation are to be determined based on object/relational mapping metadata, DDL scripts, or a combination of the two. See SourceType for the list of legal values.

If no value is specified, a default is inferred as follows:


jakarta.persistence.schema-generation.database.action

Specifies what type of schema tooling action should be performed against the database specified using either "jakarta.persistence.schema-generation-connection" or the configured ConnectionProvider for the SessionFactory.

Valid options are enumerated by Action.

This setting takes precedence over "hibernate.hbm2ddl.auto".

If no value is specified, the default is "none".


jakarta.persistence.schema-generation.drop-script-source

Specifies the DROP script file as either a Reader configured for reading the DDL script file or a string designating a file URL for the DDL script.


jakarta.persistence.schema-generation.drop-source

Specifies whether schema generation commands for schema dropping are to be determined based on object/relational mapping metadata, DDL scripts, or a combination of the two. See SourceType for the list of legal values.

If no value is specified, a default is inferred as follows:


jakarta.persistence.schema-generation.scripts.action

Specifies what type of schema tooling action should be written to script files.

Valid options are enumerated by Action.

If no value is specified, the default is "none".


jakarta.persistence.schema-generation.scripts.create-target

For cases where "jakarta.persistence.schema-generation.scripts.action" indicates that schema creation commands should be written to a script file, this setting specifies either a Writer configured for output of the DDL script or a string specifying the file URL for the DDL script.


jakarta.persistence.schema-generation.scripts.drop-target

For cases where "jakarta.persistence.schema-generation.scripts.action" indicates that schema drop commands should be written to a script file, this setting specifies either a Writer configured for output of the DDL script or a string specifying the file URL for the DDL script.


jakarta.persistence.sql-load-script-source

JPA-standard variant of HBM2DDL_IMPORT_FILES for specifying a database initialization script to be run as part of schema-export

Specifies a Reader configured for reading of the SQL load script or a string designating the URL for the SQL load script.


hibernate.dialect.storage_engine

Specifies the default storage engine for a relational databases that supports multiple storage engines. This property must be set either as an Environment variable or JVM System Property, since the Dialect is instantiated before Hibernate property resolution.


hibernate.hbm2ddl.auto

Default Value: "none"

Setting to perform SchemaManagementTool actions automatically as part of the SessionFactory lifecycle. Valid options are enumerated by Action.

Interpreted in combination with JAKARTA_HBM2DDL_DATABASE_ACTION and JAKARTA_HBM2DDL_SCRIPTS_ACTION. If no value is specified, the default is "none".


hibernate.hbm2ddl.charset_name

The name of the charset used by the schema generation resource.

By default, the JVM default charset is used.


hibernate.hbm2ddl.create_namespaces
This setting is considered deprecated

Since: 5.0

Specifies whether to automatically create also the database schema/catalog. The default is false.


hibernate.hbm2ddl.default_constraint_mode

Used with the ConstraintMode.PROVIDER_DEFAULT strategy for foreign key mapping.


hibernate.hbm2ddl.delimiter

Identifies the delimiter to use to separate schema management statements in script outputs.


hibernate.hbm2ddl.extra_physical_table_types

Specifies a comma-separated list of extra table types, in addition to the default types "TABLE" and "VIEW", to recognize as physical tables when performing schema update, creation and validation.


hibernate.hbm2ddl.halt_on_error

Since: 5.2.4

Default Value: false

When enabled, specifies that the schema migration tool should halt on any error, terminating the bootstrap process.


hibernate.hbm2ddl.import_files
This setting is considered deprecated

Specifies a comma-separated list of file names of scripts containing SQL DML statements that should be executed after schema export completes. The order of the scripts is significant, with the first script in the list being executed first.

The scripts are only executed if the schema is created by Hibernate, that is, if "hibernate.hbm2ddl.auto" is set to create or create-drop.

The default value is /import.sql.


hibernate.hbm2ddl.import_files_sql_extractor

Default Value: org.hibernate.tool.schema.internal.script.SingleLineSqlScriptExtractor.

The SqlScriptCommandExtractor implementation to use for parsing source/import files specified by JAKARTA_HBM2DDL_CREATE_SCRIPT_SOURCE, JAKARTA_HBM2DDL_DROP_SCRIPT_SOURCE or HBM2DDL_IMPORT_FILES. Either:

  • an instance of SqlScriptCommandExtractor,

  • a Class object representing a class that implements SqlScriptCommandExtractor, or

  • the name of a class that implements SqlScriptCommandExtractor.

The correct extractor to use depends on the format of the SQL script:


hibernate.hbm2ddl.jdbc_metadata_extraction_strategy

Setting to choose the strategy used to access the JDBC Metadata.

Valid options are defined by JdbcMetadaAccessStrategy. JdbcMetadaAccessStrategy.GROUPED is the default.


hibernate.hbm2ddl.schema-generation.script.append

For cases where the "jakarta.persistence.schema-generation.scripts.action" value indicates that schema commands should be written to DDL script file, specifies if schema commands should be appended to the end of the file rather than written at the beginning of the file.

Values are: true for appending schema commands to the end of the file, false for writing schema commands at the beginning.


hibernate.hbm2ddl.schema_filter_provider

Used to specify the SchemaFilterProvider to be used by create, drop, migrate and validate operations on the database schema. A SchemaFilterProvider provides filters that can be used to limit the scope of these operations to specific namespaces, tables and sequences. All objects are included by default.


hibernate.query.mutation_strategy.global_temporary.create_tables

Allows creation of global temporary tables at application startup to be disabled. By default, table creation is enabled.


hibernate.query.mutation_strategy.global_temporary.drop_tables
This setting is considered deprecated

Allows dropping of global temporary tables at application shutdown to be disabled. By default, table dropping is enabled.


hibernate.query.mutation_strategy.local_temporary.drop_tables
This setting is considered deprecated

Allows dropping of local temporary tables at transaction commit to be enabled. By default, table dropping is disabled, and the database will drop the temporary tables automatically.


hibernate.query.mutation_strategy.persistent.create_tables

Allows creation of persistent temporary tables at application startup to be disabled. By default, table creation is enabled.


hibernate.query.mutation_strategy.persistent.drop_tables

Allows dropping of persistent temporary tables at application shutdown to be disabled. By default, table dropping is enabled.


hibernate.schema_management_tool

Specifies the SchemaManagementTool to use for performing schema management.

By default, HibernateSchemaManagementTool is used.


hibernate.schema_update.unique_constraint_strategy

Unique columns and unique keys both use unique constraints in most dialects. The schema exporter must create these constraints, but database support for finding existing constraints is extremely inconsistent. Worse, unique constraints without explicit names are assigned names with randomly generated characters.

Therefore, select from these strategies:

  • DROP_RECREATE_QUIETLY: Attempt to drop, then (re-)create each unique constraint, ignoring any exceptions thrown. This is the default.

  • RECREATE_QUIETLY: Attempt to (re-)create unique constraints, ignoring exceptions thrown if the constraint already existed.

  • SKIP: Do not attempt to create unique constraints on a schema update.


hibernate.synonyms

Default Value: false

If enabled, allows schema update and validation to support synonyms. Due to the possibility that this would return duplicate tables (especially in Oracle), this is disabled by default.


A.19. Session Event Settings

hibernate.session.events.auto

Defines a default SessionEventListener to be applied to newly-opened Sessions.


hibernate.session.events.log

Controls whether session metrics should be logged for any session in which statistics are being collected.

By default, logging of session metrics is disabled unless StatisticsSettings.GENERATE_STATISTICS is enabled.


hibernate.session_factory.interceptor

Specifies an Interceptor implementation associated with the SessionFactory and propagated to each Session created from the SessionFactory. Either:

  • an instance of Interceptor,

  • a Class representing a class that implements Interceptor, or

  • the name of a class that implements Interceptor.

This setting identifies an Interceptor which is effectively a singleton across all the sessions opened from the SessionFactory to which it is applied; the same instance will be passed to each Session. If there should be a separate instance of Interceptor for each Session, use SESSION_SCOPED_INTERCEPTOR instead.


hibernate.session_factory.session_scoped_interceptor

Specifies an Interceptor implementation associated with the SessionFactory and propagated to each Session created from the SessionFactory. Either:

  • a Class representing a class that implements Interceptor,

  • the name of a class that implements Interceptor, or

  • an instance of Supplier used to obtain the interceptor.

Note that this setting cannot specify an Interceptor instance.

This setting identifies an Interceptor implementation that is to be applied to every Session opened from the SessionFactory, but unlike INTERCEPTOR, a separate instance created for each Session.


A.20. Hibernate Spatial Settings

hibernate.integration.spatial.enabled

The name of the configuration setting used to control whether the spatial integration is enabled. Default is true


hibernate.spatial.connection_finder

The canonical class name of the Oracle ConnectionFinder implementation that will be used by the Oracle spatial dialects


hibernate.spatial.db2.srid

SRID to use for the DB2 Spatial Dialects.


A.21. Statistics Settings

hibernate.generate_statistics

Default Value: false

When enabled, specifies that statistics should be collected.


hibernate.statistics.query_max_size

This setting controls the number of QueryStatistics entries that will be stored by the Hibernate Statistics object.

The default value is 5000.


hibernate.stats.factory

When statistics are enabled, names the StatisticsFactory to use. Recognizes a class name as well as an instance of StatisticsFactory.

Allows customization of how the Hibernate Statistics are collected.

A.22. Multi-tenancy Settings

hibernate.multi_tenant.datasource.identifier_for_any

During bootstrap, Hibernate needs access to any Connection for access to DatabaseMetaData.

This setting configures the name of the DataSource to use for this access

hibernate.multi_tenant_connection_provider

Specifies a MultiTenantConnectionProvider to use. Since MultiTenantConnectionProvider is also a service, it may be configured directly via the StandardServiceRegistryBuilder.


hibernate.tenant_identifier_resolver

Specifies a CurrentTenantIdentifierResolver to use, either:

  • an instance of CurrentTenantIdentifierResolver,

  • a Class representing an class that implements CurrentTenantIdentifierResolver, or

  • the name of a class that implements CurrentTenantIdentifierResolver.


A.23. Jakarta Validation Integeration Settings

jakarta.persistence.validation.factory

Used to pass along any discovered ValidatorFactory.


jakarta.persistence.validation.group.pre-persist

Used to coordinate with bean validators.

See JPA 2 section 8.2.1.9


jakarta.persistence.validation.group.pre-remove

Used to coordinate with bean validators.

See JPA 2 section 8.2.1.9


jakarta.persistence.validation.group.pre-update

Used to coordinate with bean validators.

See JPA 2 section 8.2.1.9


jakarta.persistence.validation.mode

Indicates which form of automatic validation is in effect as per the rules defined in JPA 2 section 3.6.1.1.

See JPA 2 sections 9.4.3 and 8.2.1.8


hibernate.check_nullability

Enable nullability checking, raises an exception if an attribute marked as not null is null at runtime.

Defaults to disabled if Bean Validation is present in the classpath and annotations are used, or enabled otherwise.


Appendix B: Legacy BasicType resolution

Versions prior to 6.0 statically combined the JavaType, JdbcType, BasicValueConverter and MutabilityPlan aspects within the org.hibernate.type.BasicType contract. Hibernate’s legacy strategy for resolving a basic type is based on finding the implementation of org.hibernate.type.BasicType to use.

This appendix will describe the legacy approach for influencing the mapping of basic types.

Generally speaking, this resolution uses an internal registry of BasicType implementations registered under one-or-more "registration keys". The tables in Hibernate-provided BasicTypeReferences describe the initial set of BasicType references registered by Hibernate. BasicTypeRegistry describes this BasicTypeRegistry.

Users can also override mappings in the BasicTypeRegistry or extend them to map new types, as described in Custom BasicTypes.

B.1. Hibernate-provided BasicTypeReferences

Table 11. StandardBasicTypes
StandardBasicTypes constant JDBC type Java type BasicTypeRegistry key(s)

STRING

VARCHAR

java.lang.String

string, java.lang.String

MATERIALIZED_CLOB

CLOB

java.lang.String

materialized_clob

MATERIALIZED_CLOB_CHAR_ARRAY

CHAR

char[]

materialized_clob_char_array

MATERIALIZED_CLOB_CHARACTER_ARRAY

CLOB

java.lang.Character[]

materialized_clob_character_array

TEXT

LONGVARCHAR

java.lang.String

text

CHARACTER

CHAR

char, java.lang.Character

character, char, java.lang.Character

BOOLEAN

BOOLEAN

boolean, java.lang.Boolean

boolean, java.lang.Boolean

NUMERIC_BOOLEAN

TINYINT, 0 is false, 1 is true

boolean, java.lang.Boolean

numeric_boolean

YES_NO

CHAR, 'N'/'n' is false, 'Y'/'y' is true. The uppercase value is written to the database.

boolean, java.lang.Boolean

yes_no

TRUE_FALSE

CHAR, 'F'/'f' is false, 'T'/'t' is true. The uppercase value is written to the database.

boolean, java.lang.Boolean

true_false

BYTE

TINYINT

byte, java.lang.Byte

byte, java.lang.Byte

SHORT

SMALLINT

short, java.lang.Short

short, java.lang.Short

INTEGER

INTEGER

int, java.lang.Integer

integer, int, java.lang.Integer

LONG

BIGINT

long, java.lang.Long

long, java.lang.Long

FLOAT

FLOAT

float, java.lang.Float

float, java.lang.Float

DOUBLE

DOUBLE

double, java.lang.Double

double, java.lang.Double

BIG_INTEGER

NUMERIC

java.math.BigInteger

big_integer, java.math.BigInteger

BIG_DECIMAL

NUMERIC

java.math.BigDecimal

big_decimal, java.math.bigDecimal

TIMESTAMP

TIMESTAMP

java.util.Date

timestamp, java.sql.Timestamp, java.util.Date

TIME

TIME

java.util.Date

time, java.sql.Time

DATE

DATE

java.util.Date

date, java.sql.Date

CALENDAR

TIMESTAMP

java.util.Calendar

calendar, java.util.Calendar, java.util.GregorianCalendar

CALENDAR_DATE

DATE

java.util.Calendar

calendar_date

CALENDAR_TIME

TIME

java.util.Calendar

calendar_time

CURRENCY

VARCHAR

java.util.Currency

currency, java.util.Currency

LOCALE

VARCHAR

java.util.Locale

locale, java.util.Locale

TIMEZONE

VARCHAR, using the TimeZone ID

java.util.TimeZone

timezone, java.util.TimeZone

URL

VARCHAR

java.net.URL

url, java.net.URL

CLASS

VARCHAR (class FQN)

java.lang.Class

class, java.lang.Class

BLOB

BLOB

java.sql.Blob

blob, java.sql.Blob

CLOB

CLOB

java.sql.Clob

clob, java.sql.Clob

BINARY

VARBINARY

byte[]

binary, byte[]

MATERIALIZED_BLOB

BLOB

byte[]

materialized_blob

IMAGE

LONGVARBINARY

byte[]

image

BINARY_WRAPPER

VARBINARY

java.lang.Byte[]

binary_wrapper, wrapper-binary, Byte[], java.lang.Byte[]

MATERIALIZED_BLOB_WRAPPER

BLOB

java.lang.Byte[]

materialized_blob_wrapper

CHAR_ARRAY

VARCHAR

char[]

characters, char[]

CHARACTER_ARRAY

VARCHAR

java.lang.Character[]

wrapper-characters, Character[], java.lang.Character[]

UUID

UUID or BINARY

java.util.UUID

uuid, java.util.UUID, pg-uuid

UUID_BINARY

BINARY

java.util.UUID

uuid-binary, java.util.UUID

UUID_CHAR

CHAR, can also read VARCHAR

java.util.UUID

uuid-char

SERIALIZABLE

VARBINARY

implementors of java.lang.Serializable

Unlike the other value types, multiple instances of this type are registered. It is registered once under java.io.Serializable, and registered under the specific java.io.Serializable implementation class names.

NSTRING

NVARCHAR

java.lang.String

nstring

NTEXT

LONGNVARCHAR

java.lang.String

ntext

NCLOB

NCLOB

java.sql.NClob

nclob, java.sql.NClob

MATERIALIZED_NCLOB

NCLOB

java.lang.String

materialized_nclob

MATERIALIZED_NCLOB_CHAR_ARRAY

NCHAR

char[]

materialized_nclob_char_array

CHARACTER_NCHAR

NCHAR

java.lang.Character

ncharacter

MATERIALIZED_NCLOB_CHARACTER_ARRAY

NCLOB

java.lang.Character[]

materialized_nclob_character_array

ROW_VERSION

VARBINARY

byte[]

row_version

OBJECT_TYPE

VARCHAR

implementors of java.lang.Serializable

object, java.lang.Object

Table 12. Java 8 StandardBasicTypes
Hibernate type (org.hibernate.type package) JDBC type Java type BasicTypeRegistry key(s)

DURATION

NUMERIC

java.time.Duration

Duration, java.time.Duration

INSTANT

TIMESTAMP_UTC

java.time.Instant

Instant, java.time.Instant

LOCAL_DATE_TIME

TIMESTAMP

java.time.LocalDateTime

LocalDateTime, java.time.LocalDateTime

LOCAL_DATE

DATE

java.time.LocalDate

LocalDate, java.time.LocalDate

LOCAL_TIME

TIME

java.time.LocalTime

LocalTime, java.time.LocalTime

OFFSET_DATE_TIME

TIMESTAMP_WITH_TIMEZONE

java.time.OffsetDateTime

OffsetDateTime, java.time.OffsetDateTime

OFFSET_DATE_TIME_WITH_TIMEZONE

TIMESTAMP_WITH_TIMEZONE

java.time.OffsetDateTime

OffsetDateTime, java.time.OffsetDateTime

OFFSET_DATE_TIME_WITHOUT_TIMEZONE

TIMESTAMP

java.time.OffsetDateTime

OffsetDateTime, java.time.OffsetDateTime

OFFSET_TIME

TIME

java.time.OffsetTime

OffsetTime, java.time.OffsetTime

ZONED_DATE_TIME

TIMESTAMP_WITH_TIMEZONE

java.time.ZonedDateTime

ZonedDateTime, java.time.ZonedDateTime

ZONED_DATE_TIME_WITH_TIMEZONE

TIMESTAMP_WITH_TIMEZONE

java.time.ZonedDateTime

ZonedDateTimeWithTimezone

ZONED_DATE_TIME_WITHOUT_TIMEZONE

TIMESTAMP

java.time.ZonedDateTime

ZonedDateTimeWithoutTimezone

ZONE_OFFSET

VARCHAR

java.time.ZoneOffset

ZoneOffset, java.time.ZoneOffset

B.2. BasicTypeRegistry

We said before that a Hibernate type is not a Java type, nor an SQL type, but that it understands both and performs the marshalling between them. But looking at the basic type mappings from the previous examples, how did Hibernate know to use its org.hibernate.type.StandardBasicTypes.STRING for mapping for java.lang.String attributes, or its org.hibernate.type.StandardBasicTypes.INTEGER for mapping java.lang.Integer attributes?

The answer lies in a service inside Hibernate called the org.hibernate.type.BasicTypeRegistry, which maintains a map of org.hibernate.type.BasicType and org.hibernate.type.BasicTypeReference instances keyed by a name.

We will see later, in the Explicit BasicTypes section, that we can explicitly tell Hibernate which BasicType to use for a particular attribute. But first, let’s explore how implicit resolution works and how applications can adjust the implicit resolution.

A thorough discussion of BasicTypeRegistry and all the different ways to contribute types is beyond the scope of this documentation.

Please see the Integration Guide for complete details.

As an example, take a String attribute such as we saw before with Product#sku. Since there is no explicit type mapping, Hibernate looks to the BasicTypeRegistry to find the registered mapping for java.lang.String.

As a baseline within BasicTypeRegistry, Hibernate follows the recommended mappings of JDBC for Java types. JDBC recommends mapping Strings to VARCHAR, which is the exact mapping that StringType handles. So that is the baseline mapping within BasicTypeRegistry for Strings.

Applications can also extend (add new BasicType registrations) or override (replace an existing BasicType registration) using one of the MetadataBuilder#applyBasicType methods or the MetadataBuilder#applyTypes method during bootstrap. For more details, see Custom BasicTypes section.

B.3. Explicit BasicTypes

Sometimes you want a particular attribute to be handled differently. Occasionally Hibernate will implicitly pick a BasicType that you do not want (and for some reason you do not want to adjust the BasicTypeRegistry).

In these cases, you must explicitly tell Hibernate the BasicType to use, via the org.hibernate.annotations.Type annotation.

Example 698. Using @org.hibernate.annotations.Type
@Entity(name = "Product")
public class Product {

	@Id
	private Integer id;

	private String sku;

	@Type(
			value = UserTypeLegacyBridge.class,
			parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "nstring")
	)
	private String name;

	@Type(
			value = UserTypeLegacyBridge.class,
			parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "materialized_nclob")
	)
	private String description;
}

This tells Hibernate to store the Strings as nationalized data. This is just for illustration purposes; for better ways to indicate nationalized character data see Handling nationalized character data section.

Additionally, the description is to be handled as a LOB. Again, for better ways to indicate LOBs see Handling LOB data section.

The org.hibernate.annotations.Type#value attribute can refers to a org.hibernate.type.UserType class which can be configured further by specifying org.hibernate.annotations.Type#parameters.

The special user type org.hibernate.usertype.UserTypeLegacyBridge provides a way to bridge the gap between the named type use before Hibernate 6.0 and the new strongly typed nature of org.hibernate.annotations.Type.

B.4. Custom BasicTypes

Hibernate makes it relatively easy for developers to create their own basic type mappings type. For example, you might want to persist properties of type java.util.BigInteger to VARCHAR columns, or support completely new types.

There are two approaches to developing a custom type:

  • implementing a BasicType and registering it

  • implementing a UserType which doesn’t require type registration

As a means of illustrating the different approaches, let’s consider a use case where we need to support a java.util.BitSet mapping that’s stored as a VARCHAR.

B.4.1. Implementing a BasicType

The first approach is to directly implement the BasicType interface.

Because the BasicType interface has a lot of methods to implement, if the value is stored in a single database column, it’s much more convenient to extend the AbstractStandardBasicType or the AbstractSingleColumnStandardBasicType Hibernate classes.

First, we need to extend the AbstractSingleColumnStandardBasicType like this:

Example 699. Custom BasicType implementation
public class BitSetType
        extends AbstractSingleColumnStandardBasicType<BitSet> {

    public static final BitSetType INSTANCE = new BitSetType();

    public BitSetType() {
        super( VarcharJdbcType.INSTANCE, BitSetJavaType.INSTANCE );
    }

    @Override
    public String getName() {
        return "bitset";
    }

}

The AbstractSingleColumnStandardBasicType requires an jdbcType and a javaType. The jdbcType is VarcharJdbcType.INSTANCE because the database column is a VARCHAR. On the Java side, we need to use a BitSetJavaType instance which can be implemented like this:

Example 700. Custom JavaType implementation
public class BitSetJavaType extends AbstractClassJavaType<BitSet> {
    public static final BitSetJavaType INSTANCE = new BitSetJavaType();

    public BitSetJavaType() {
        super(BitSet.class);
    }

    @Override
    public MutabilityPlan<BitSet> getMutabilityPlan() {
        return BitSetMutabilityPlan.INSTANCE;
    }

    @Override
    public JdbcType getRecommendedJdbcType(JdbcTypeIndicators indicators) {
        return indicators.getTypeConfiguration()
                .getJdbcTypeRegistry()
                .getDescriptor(Types.VARCHAR);
    }

    @Override
    public String toString(BitSet value) {
        return BitSetHelper.bitSetToString(value);
    }

    @Override
    public BitSet fromString(CharSequence string) {
        return BitSetHelper.stringToBitSet(string.toString());
    }

    @SuppressWarnings("unchecked")
    public <X> X unwrap(BitSet value, Class<X> type, WrapperOptions options) {
        if (value == null) {
            return null;
        }
        if (BitSet.class.isAssignableFrom(type)) {
            return (X) value;
        }
        if (String.class.isAssignableFrom(type)) {
            return (X) toString(value);
        }
        if (type.isArray()) {
            if (type.getComponentType() == byte.class) {
                return (X) value.toByteArray();
            }
        }
        throw unknownUnwrap(type);
    }

    public <X> BitSet wrap(X value, WrapperOptions options) {
        if (value == null) {
            return null;
        }
        if (value instanceof CharSequence) {
            return fromString((CharSequence) value);
        }
        if (value instanceof BitSet) {
            return (BitSet) value;
        }
        throw unknownWrap(value.getClass());
    }

}

The unwrap() method is used when passing a BitSet as a PreparedStatement bind parameter, while the wrap() method is used to transform the JDBC column value object (e.g. String in our case) to the actual mapping object type (e.g. BitSet in this example).

The BasicType must be registered, and this can be done at bootstrapping time:

Example 701. Register a Custom BasicType implementation
configuration.registerTypeContributor( (typeContributions, serviceRegistry) -> {
	typeContributions.contributeType( BitSetType.INSTANCE );
} );

or using the MetadataBuilder

ServiceRegistry standardRegistry =
        new StandardServiceRegistryBuilder().build();

MetadataSources sources = new MetadataSources( standardRegistry );

MetadataBuilder metadataBuilder = sources.getMetadataBuilder();

metadataBuilder.applyBasicType( BitSetType.INSTANCE );

With the new BitSetType being registered as bitset, the entity mapping looks like this:

Example 702. Custom BasicType mapping
@Entity(name = "Product")
public static class Product {

	@Id
	private Integer id;

	@Type(
			value = UserTypeLegacyBridge.class,
			parameters = @Parameter(name = UserTypeLegacyBridge.TYPE_NAME_PARAM_KEY, value = "bitset")
	)
	private BitSet bitSet;

	public Integer getId() {
		return id;
	}

	//Getters and setters are omitted for brevity
}

To validate this new BasicType implementation, we can test it as follows:

Example 703. Persisting the custom BasicType
BitSet bitSet = BitSet.valueOf( new long[] {1, 2, 3} );

doInHibernate( this::sessionFactory, session -> {
	Product product = new Product( );
	product.setId( 1 );
	product.setBitSet( bitSet );
	session.persist( product );
} );

doInHibernate( this::sessionFactory, session -> {
	Product product = session.get( Product.class, 1 );
	assertEquals(bitSet, product.getBitSet());
} );

When executing this unit test, Hibernate generates the following SQL statements:

Example 704. Persisting the custom BasicType
DEBUG SQL:92 -
    insert
    into
        Product
        (bitSet, id)
    values
        (?, ?)

TRACE BasicBinder:65 - binding parameter [1] as [VARCHAR] - [{0, 65, 128, 129}]
TRACE BasicBinder:65 - binding parameter [2] as [INTEGER] - [1]

DEBUG SQL:92 -
    select
        bitsettype0_.id as id1_0_0_,
        bitsettype0_.bitSet as bitSet2_0_0_
    from
        Product bitsettype0_
    where
        bitsettype0_.id=?

TRACE BasicBinder:65 - binding parameter [1] as [INTEGER] - [1]
TRACE BasicExtractor:61 - extracted value ([bitSet2_0_0_] : [VARCHAR]) - [{0, 65, 128, 129}]

As you can see, the BitSetType takes care of the Java-to-SQL and SQL-to-Java type conversion.

B.4.2. Implementing a UserType

The second approach is to implement the UserType interface.

Example 705. Custom UserType implementation
public class BitSetUserType implements UserType<BitSet> {

    private static final Logger log = Logger.getLogger(BitSetUserType.class);

    @Override
    public int getSqlType() {
        return Types.VARCHAR;
    }

    @Override
    public Class<BitSet> returnedClass() {
        return BitSet.class;
    }

    @Override
    public boolean equals(BitSet x, BitSet y) {
        return Objects.equals(x, y);
    }

    @Override
    public int hashCode(BitSet x) {
        return Objects.hashCode(x);
    }

    @Override
    public BitSet nullSafeGet(ResultSet rs, int position,
                              SharedSessionContractImplementor session, Object owner)
            throws SQLException {
        String columnValue = rs.getString(position);
        if (rs.wasNull()) {
            columnValue = null;
        }

        log.debugv("Result set column {0} value is {1}", position, columnValue);
        return BitSetHelper.stringToBitSet(columnValue);
    }

    @Override
    public void nullSafeSet(PreparedStatement st, BitSet value, int index,
                            SharedSessionContractImplementor session)
            throws SQLException {
        if (value == null) {
            log.debugv("Binding null to parameter {0} ",index);
            st.setNull(index, Types.VARCHAR);
        }
        else {
            String stringValue = BitSetHelper.bitSetToString(value);
            log.debugv("Binding {0} to parameter {1} ", stringValue, index);
            st.setString(index, stringValue);
        }
    }

    @Override
    public BitSet deepCopy(BitSet bitSet) {
        return bitSet == null ? null : (BitSet) bitSet.clone();
    }

    @Override
    public boolean isMutable() {
        return true;
    }

    @Override
    public Serializable disassemble(BitSet value) {
        return deepCopy(value);
    }

    @Override
    public BitSet assemble(Serializable cached, Object owner)  {
        return deepCopy((BitSet) cached);
    }
}

The entity mapping looks as follows:

Example 706. Custom UserType mapping
@Entity(name = "Product")
public static class Product {

	@Id
	private Integer id;

	@Type(BitSetUserType.class)
	@Column(name = "bitset_col")
	private BitSet bitSet;

	//Constructors, getters, and setters are omitted for brevity
}

In this example, the UserType is registered under the bitset name, and this is done like this:

Example 707. Register a Custom UserType implementation
configuration.registerTypeContributor( (typeContributions, serviceRegistry) -> {
	typeContributions.contributeType( BitSetUserType.INSTANCE, "bitset");
} );

or using the MetadataBuilder

ServiceRegistry standardRegistry =
    new StandardServiceRegistryBuilder().build();

MetadataSources sources = new MetadataSources(standardRegistry);

MetadataBuilder metadataBuilder = sources.getMetadataBuilder();

metadataBuilder.applyBasicType(new BitSetUserType(), "bitset");

When running the previous test case against the BitSetUserType entity mapping, Hibernate executed the following SQL statements:

Example 708. Persisting the custom BasicType
DEBUG SQL:92 -
    insert
    into
        Product
        (bitSet, id)
    values
        (?, ?)

DEBUG BitSetUserType:71 - Binding 1,10,11 to parameter 1
TRACE BasicBinder:65 - binding parameter [2] as [INTEGER] - [1]

DEBUG SQL:92 -
    select
        bitsetuser0_.id as id1_0_0_,
        bitsetuser0_.bitSet as bitSet2_0_0_
    from
        Product bitsetuser0_
    where
        bitsetuser0_.id=?

TRACE BasicBinder:65 - binding parameter [1] as [INTEGER] - [1]
DEBUG BitSetUserType:56 - Result set column bitSet2_0_0_ value is 1,10,11

Appendix C: Legacy Hibernate Native Queries

C.1. Legacy named SQL queries

Named SQL queries can also be defined during mapping and called in exactly the same way as a named HQL query. In this case, you do not need to call addEntity() anymore.

Example 709. Named sql query using the <sql-query> mapping element
<sql-query name = "persons">
    <return alias="person" class="eg.Person"/>
    SELECT person.NAME AS {person.name},
           person.AGE AS {person.age},
           person.SEX AS {person.sex}
    FROM PERSON person
    WHERE person.NAME LIKE :namePattern
</sql-query>
Example 710. Execution of a named query
List people = session
    .getNamedQuery( "persons" )
    .setParameter( "namePattern", namePattern )
    .setMaxResults( 50 )
    .list();

The <return-join> element is use to join associations and the <load-collection> element is used to define queries which initialize collections.

Example 711. Named sql query with association
<sql-query name = "personsWith">
    <return alias="person" class="eg.Person"/>
    <return-join alias="address" property="person.mailingAddress"/>
    SELECT person.NAME AS {person.name},
           person.AGE AS {person.age},
           person.SEX AS {person.sex},
           address.STREET AS {address.street},
           address.CITY AS {address.city},
           address.STATE AS {address.state},
           address.ZIP AS {address.zip}
    FROM PERSON person
    JOIN ADDRESS address
        ON person.ID = address.PERSON_ID AND address.TYPE='MAILING'
    WHERE person.NAME LIKE :namePattern
</sql-query>

A named SQL query may return a scalar value. You must declare the column alias and Hibernate type using the <return-scalar> element:

Example 712. Named query returning a scalar
<sql-query name = "mySqlQuery">
    <return-scalar column = "name" type="string"/>
    <return-scalar column = "age" type="long"/>
    SELECT p.NAME AS name,
           p.AGE AS age,
    FROM PERSON p WHERE p.NAME LIKE 'Hiber%'
</sql-query>

You can externalize the resultset mapping information in a <resultset> element which will allow you to either reuse them across several named queries or through the setResultSetMapping() API.

Example 713. <resultset> mapping used to externalize mapping information
<resultset name = "personAddress">
    <return alias="person" class="eg.Person"/>
    <return-join alias="address" property="person.mailingAddress"/>
</resultset>

<sql-query name = "personsWith" resultset-ref="personAddress">
    SELECT person.NAME AS {person.name},
           person.AGE AS {person.age},
           person.SEX AS {person.sex},
           address.STREET AS {address.street},
           address.CITY AS {address.city},
           address.STATE AS {address.state},
           address.ZIP AS {address.zip}
    FROM PERSON person
    JOIN ADDRESS address
        ON person.ID = address.PERSON_ID AND address.TYPE='MAILING'
    WHERE person.NAME LIKE :namePattern
</sql-query>

You can, alternatively, use the resultset mapping information in your hbm files directly in Java code.

Example 714. Programmatically specifying the result mapping information
List cats = session
    .createSQLQuery( "select {cat.*}, {kitten.*} from cats cat, cats kitten where kitten.mother = cat.id" )
    .setResultSetMapping( "catAndKitten" )
    .list();

C.2. Legacy return-property to explicitly specify column/alias names

You can explicitly tell Hibernate what column aliases to use with <return-property>, instead of using the {} syntax to let Hibernate inject its own aliases. For example:

<sql-query name = "mySqlQuery">
    <return alias = "person" class = "eg.Person">
        <return-property name = "name" column = "myName"/>
        <return-property name = "age" column = "myAge"/>
        <return-property name = "sex" column = "mySex"/>
    </return>
    SELECT person.NAME AS myName,
           person.AGE AS myAge,
           person.SEX AS mySex,
    FROM PERSON person WHERE person.NAME LIKE :name
</sql-query>

<return-property> also works with multiple columns. This solves a limitation with the {} syntax which cannot allow fine grained control of multi-column properties.

<sql-query name = "organizationCurrentEmployments">
    <return alias = "emp" class = "Employment">
        <return-property name = "salary">
            <return-column name = "VALUE"/>
            <return-column name = "CURRENCY"/>
        </return-property>
        <return-property name = "endDate" column = "myEndDate"/>
    </return>
        SELECT EMPLOYEE AS {emp.employee}, EMPLOYER AS {emp.employer},
        STARTDATE AS {emp.startDate}, ENDDATE AS {emp.endDate},
        REGIONCODE as {emp.regionCode}, EID AS {emp.id}, VALUE, CURRENCY
        FROM EMPLOYMENT
        WHERE EMPLOYER = :id AND ENDDATE IS NULL
        ORDER BY STARTDATE ASC
</sql-query>

In this example <return-property> was used in combination with the {} syntax for injection. This allows users to choose how they want to refer column and properties.

If your mapping has a discriminator you must use <return-discriminator> to specify the discriminator column.

C.3. Legacy stored procedures for querying

Hibernate provides support for queries via stored procedures and functions. Most of the following documentation is equivalent for both. The stored procedure/function must return a resultset as the first out-parameter to be able to work with Hibernate. An example of such a stored function in Oracle 9 and higher is as follows:

CREATE OR REPLACE FUNCTION selectAllEmployments
    RETURN SYS_REFCURSOR
AS
    st_cursor SYS_REFCURSOR;
BEGIN
    OPEN st_cursor FOR
        SELECT EMPLOYEE, EMPLOYER,
        STARTDATE, ENDDATE,
        REGIONCODE, EID, VALUE, CURRENCY
        FROM EMPLOYMENT;
    RETURN  st_cursor;
END;

To use this query in Hibernate you need to map it via a named query.

<sql-query name = "selectAllEmployees_SP" callable = "true">
    <return alias="emp" class="Employment">
        <return-property name = "employee" column = "EMPLOYEE"/>
        <return-property name = "employer" column = "EMPLOYER"/>
        <return-property name = "startDate" column = "STARTDATE"/>
        <return-property name = "endDate" column = "ENDDATE"/>
        <return-property name = "regionCode" column = "REGIONCODE"/>
        <return-property name = "id" column = "EID"/>
        <return-property name = "salary">
            <return-column name = "VALUE"/>
            <return-column name = "CURRENCY"/>
        </return-property>
    </return>
    { ? = call selectAllEmployments() }
</sql-query>

Stored procedures currently only return scalars and entities. <return-join> and <load-collection> are not supported.

C.4. Legacy rules/limitations for using stored procedures

You cannot use stored procedures with Hibernate unless you follow some procedure/function rules. If they do not follow those rules they are not usable with Hibernate. If you still want to use these procedures you have to execute them via session.doWork().

The rules are different for each database since database vendors have different stored procedure semantics/syntax.

Stored procedure queries cannot be paged with setFirstResult()/setMaxResults().

The recommended call form is standard SQL92: { ? = call functionName(<parameters>) } or { ? = call procedureName(<parameters>}. Native call syntax is not supported.

For Oracle the following rules apply:

  • A function must return a result set.

  • The first parameter of a procedure must be an OUT that returns a result set. This is done by using a SYS_REFCURSOR type in Oracle 9 or 10. In Oracle you need to define a REF CURSOR type. See Oracle literature for further information.

For Sybase or MS SQL server the following rules apply:

  • The procedure must return a result set. Note that since these servers can return multiple result sets and update counts, Hibernate will iterate the results and take the first result that is a result set as its return value. Everything else will be discarded.

  • If you can enable SET NOCOUNT ON in your procedure it will probably be more efficient, but this is not a requirement.

C.5. Legacy custom SQL for create, update and delete

Hibernate can use custom SQL for create, update, and delete operations. The SQL can be overridden at the statement level or individual column level. This section describes statement overrides. For columns, see Column transformers: read and write expressions. The following example shows how to define custom SQL operations using annotations.

Example 715. Custom CRUD XML
<class name = "Person">
    <id name = "id">
        <generator class = "increment"/>
    </id>
    <property name = "name" not-null = "true"/>
    <sql-insert>INSERT INTO PERSON (NAME, ID) VALUES ( UPPER(?), ? )</sql-insert>
    <sql-update>UPDATE PERSON SET NAME=UPPER(?) WHERE ID=?</sql-update>
    <sql-delete>DELETE FROM PERSON WHERE ID=?</sql-delete>
</class>

If you expect to call a stored procedure, be sure to set the callable attribute to true in both annotation and XML-based mappings.

To check that the execution happens correctly, Hibernate allows you to define one of those three strategies:

  • none: no check is performed; the store procedure is expected to fail upon issues

  • count: use of rowcount to check that the update is successful

  • param: like COUNT but using an output parameter rather that the standard mechanism

To define the result check style, use the check parameter which is again available in annotations as well as in xml.

Last but not least, stored procedures are in most cases required to return the number of rows inserted, updated and deleted. Hibernate always registers the first statement parameter as a numeric output parameter for the CUD operations:

Example 716. Stored procedures and their return value
CREATE OR REPLACE FUNCTION updatePerson (uid IN NUMBER, uname IN VARCHAR2)
    RETURN NUMBER IS
BEGIN

    update PERSON
    set
        NAME = uname,
    where
        ID = uid;

    return SQL%ROWCOUNT;

END updatePerson;

C.6. Legacy custom SQL for loading

You can also declare your own SQL (or HQL) queries for entity loading. As with inserts, updates, and deletes, this can be done at the individual column level as described in For columns, see Column transformers: read and write expressions or at the statement level. Here is an example of a statement level override:

<sql-query name = "person">
    <return alias = "pers" class = "Person" lock-mode= "upgrade"/>
    SELECT NAME AS {pers.name}, ID AS {pers.id}
    FROM PERSON
    WHERE ID=?
    FOR UPDATE
</sql-query>

This is just a named query declaration, as discussed earlier. You can reference this named query in a class mapping:

<class name = "Person">
    <id name = "id">
        <generator class = "increment"/>
    </id>
    <property name = "name" not-null = "true"/>
    <loader query-ref = "person"/>
</class>

This even works with stored procedures.

You can even define a query for collection loading:

<set name = "employments" inverse = "true">
    <key/>
    <one-to-many class = "Employment"/>
    <loader query-ref = "employments"/>
</set>
<sql-query name = "employments">
    <load-collection alias = "emp" role = "Person.employments"/>
    SELECT {emp.*}
    FROM EMPLOYMENT emp
    WHERE EMPLOYER = :id
    ORDER BY STARTDATE ASC, EMPLOYEE ASC
</sql-query>

You can also define an entity loader that loads a collection by join fetching:

<sql-query name = "person">
    <return alias = "pers" class = "Person"/>
    <return-join alias = "emp" property = "pers.employments"/>
    SELECT NAME AS {pers.*}, {emp.*}
    FROM PERSON pers
    LEFT OUTER JOIN EMPLOYMENT emp
        ON pers.ID = emp.PERSON_ID
    WHERE ID=?
</sql-query>

Appendix D: Monitoring with Java Flight Recorder

Hibernate can provide an integration with Java Flight Recorder in order to monitor low level events. The Events that can be monitored are :

  • org.hibernate.orm.SessionOpen and org.hibernate.orm.SessionClosed to respectively monitor the opening and closing of a Hibernate Session

  • org.hibernate.orm.JdbcConnectionAcquisition and org.hibernate.orm.JdbcConnectionRelease to respectively monitor the acquisition and release of a JDBC connection

  • org.hibernate.orm.JdbcPreparedStatementCreation and org.hibernate.orm.JdbcPreparedStatementExecution to respectively monitor PreparedStatements creation and execution

  • org.hibernate.orm.JdbcBatchExecution to monitor batching execution

  • org.hibernate.orm.CachePut and org.hibernate.orm.CacheGet to respectively monitor second level cache PUT and GET operations

  • org.hibernate.orm.FlushEvent to monitor flush execution and org.hibernate.orm.PartialFlushEvent to monitor a partial flush execution

  • org.hibernate.orm.DirtyCalculationEvent to monitor dirty check calculations

To use the Java Flight Recorder integration, the application must include the hibernate-jfr jar on the classpath

The hibernate-jfr integration requires a JDK 17 supporting JFR events. It should also work with a JDK 11 supporting JFR events, but we haven’t tested it .

References


1. Jakarta Persistence’s support for Serializable types is to directly serialize their state to the database
2. For details see org.hibernate.mapping.BasicValue#resolve()
3. Only in-DB generation requires the refresh