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Hibernate understands both the Java and JDBC representations of application data. The ability to read and write
object data to a database is called marshalling, and is the function of a Hibernate
type. A type is an implementation of the
org.hibernate.type.Type interface. A Hibernate type describes
various aspects of behavior of the Java type such as how to check for equality and how to clone values.
A Hibernate type is neither a Java type nor a SQL datatype. It provides information about
both of these.
When you encounter the term type in regards to Hibernate, it may refer to the Java type, the JDBC type, or the Hibernate type, depending on context.
Hibernate categorizes types into two high-level groups: Section 8.1, “Value types” and Section 8.2, “Entity Types”.
A value type does not define its own lifecycle. It is, in effect, owned by an Section 8.2, “Entity Types”, which defines its lifecycle. Value types are further classified into three sub-categories.
Basic value types usually map a single database value, or column, to a single, non-aggregated Java type. Hibernate provides a number of built-in basic types, which follow the natural mappings recommended in the JDBC specifications. You can override these mappings and provide and use alternative mappings. These topics are discussed further on.
Table 8.1. Basic Type Mappings
| Hibernate type | Database type | JDBC type | Type registry |
|---|---|---|---|
| org.hibernate.type.StringType | string | VARCHAR | string, java.lang.String |
| org.hibernate.type.MaterializedClob | string | CLOB | materialized_clob |
| org.hibernate.type.TextType | string | LONGVARCHAR | text |
| org.hibernate.type.CharacterType | char, java.lang.Character | CHAR | char, java.lang.Character |
| org.hibernate.type.BooleanType | boolean | BIT | boolean, java.lang.Boolean |
| org.hibernate.type.NumericBooleanType | boolean | INTEGER, 0 is false, 1 is true | numeric_boolean |
| org.hibernate.type.YesNoType | boolean | CHAR, 'N'/'n' is false, 'Y'/'y' is true. The uppercase value is written to the database. | yes_no |
| org.hibernate.type.TrueFalseType | boolean | CHAR, 'F'/'f' is false, 'T'/'t' is true. The uppercase value is written to the database. | true_false |
| org.hibernate.type.ByteType | byte, java.lang.Byte | TINYINT | byte, java.lang.Byte |
| org.hibernate.type.ShortType | short, java.lang.Short | SMALLINT | short, java.lang.Short |
| org.hibernate.type.IntegerTypes | int, java.lang.Integer | INTEGER | int, java.lang.Integer |
| org.hibernate.type.LongType | long, java.lang.Long | BIGINT | long, java.lang.Long |
| org.hibernate.type.FloatType | float, java.lang.Float | FLOAT | float, java.lang.Float |
| org.hibernate.type.DoubleType | double, java.lang.Double | DOUBLE | double, java.lang.Double |
| org.hibernate.type.BigIntegerType | java.math.BigInteger | NUMERIC | big_integer |
| org.hibernate.type.BigDecimalType | java.math.BigDecimal | NUMERIC | big_decimal, java.math.bigDecimal |
| org.hibernate.type.TimestampType | java.sql.Timestamp | TIMESTAMP | timestamp, java.sql.Timestamp |
| org.hibernate.type.TimeType | java.sql.Time | TIME | time, java.sql.Time |
| org.hibernate.type.DateType | java.sql.Date | DATE | date, java.sql.Date |
| org.hibernate.type.CalendarType | java.util.Calendar | TIMESTAMP | calendar, java.util.Calendar |
| org.hibernate.type.CalendarDateType | java.util.Calendar | DATE | calendar_date |
| org.hibernate.type.CurrencyType | java.util.Currency | VARCHAR | currency, java.util.Currency |
| org.hibernate.type.LocaleType | java.util.Locale | VARCHAR | locale, java.utility.locale |
| org.hibernate.type.TimeZoneType | java.util.TimeZone | VARCHAR, using the TimeZone ID | timezone, java.util.TimeZone |
| org.hibernate.type.UrlType | java.net.URL | VARCHAR | url, java.net.URL |
| org.hibernate.type.ClassType | java.lang.Class | VARCHAR, using the class name | class, java.lang.Class |
| org.hibernate.type.BlobType | java.sql.Blob | BLOB | blog, java.sql.Blob |
| org.hibernate.type.ClobType | java.sql.Clob | CLOB | clob, java.sql.Clob |
| org.hibernate.type.BinaryType | primitive byte[] | VARBINARY | binary, byte[] |
| org.hibernate.type.MaterializedBlobType | primitive byte[] | BLOB | materized_blob |
| org.hibernate.type.ImageType | primitive byte[] | LONGVARBINARY | image |
| org.hibernate.type.BinaryType | java.lang.Byte[] | VARBINARY | wrapper-binary |
| org.hibernate.type.CharArrayType | char[] | VARCHAR | characters, char[] |
| org.hibernate.type.CharacterArrayType | java.lang.Character[] | VARCHAR | wrapper-characters, Character[], java.lang.Character[] |
| org.hibernate.type.UUIDBinaryType | java.util.UUID | BINARY | uuid-binary, java.util.UUID |
| org.hibernate.type.UUIDCharType | java.util.UUID | CHAR, can also read VARCHAR | uuid-char |
| org.hibernate.type.PostgresUUIDType | java.util.UUID | PostgreSQL UUID, through Types#OTHER, which complies to the PostgreSQL JDBC driver definition | pg-uuid |
| org.hibernate.type.SerializableType | implementors of java.lang.Serializable | VARBINARY | 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. |
Composite types, or embedded types, as they are called by the Java Persistence API, have traditionally been called components in Hibernate. All of these terms mean the same thing.
Components represent aggregations of values into a single Java type. An example is an
Address class, which aggregates street, city, state, and postal code. A composite type
behaves in a similar way to an entity. They are each classes written specifically for an application. They may
both include references to other application-specific classes, as well as to collections and simple JDK
types. The only distinguishing factors are that a component does not have its own lifecycle or define an
identifier.
Entities are application-specific classes which correlate to rows in a table, using a unique identifier. Because of the requirement for a unique identifier, ntities exist independently and define their own lifecycle. As an example, deleting a Membership should not delete the User or the Group. For more information, see the chapter on Persistent Classes.
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