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Kapitel 18. Native SQL

18.1. Using a SQLQuery
18.1.1. Skalare Anfragen
18.1.2. Entity-Anfragen
18.1.3. Umgang mit Assoziationen und Collections
18.1.4. Wiedergabe mehrerer Entities
18.1.5. Wiedergabe nicht gemanagter Entities
18.1.6. Umgang mit Vererbung
18.1.7. Parameter
18.2. Benannte SQL-Anfragen
18.2.1. Die Verwendung der Return-Property zur expliziten Spezifizierung von Spalten-/Aliasnamen
18.2.2. Die Verwendung gespeicherter Prozeduren für Anfragen
18.3. Anwenderspezifische SQL für "create" (erstellen), "update" (aktualisieren) und "delete" (löschen)
18.4. Angepasste SQL für das Laden

You can also express queries in the native SQL dialect of your database. This is useful if you want to utilize database-specific features such as query hints or the CONNECT keyword in Oracle. It also provides a clean migration path from a direct SQL/JDBC based application to Hibernate.

Hibernate3 allows you to specify handwritten SQL, including stored procedures, for all create, update, delete, and load operations.

Execution of native SQL queries is controlled via the SQLQuery interface, which is obtained by calling Session.createSQLQuery(). The following sections describe how to use this API for querying.

Die grundlegendste SQL-Anfrage erfolgt durch eine Liste von Skalaren (Werten).

sess.createSQLQuery("SELECT * FROM CATS").list();

sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").list();

These will return a List of Object arrays (Object[]) with scalar values for each column in the CATS table. Hibernate will use 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():

sess.createSQLQuery("SELECT * FROM CATS")

 .addScalar("ID", Hibernate.LONG)
 .addScalar("NAME", Hibernate.STRING)
 .addScalar("BIRTHDATE", Hibernate.DATE)

Diese Anfrage spezifiziert:

This will return Object arrays, but now it will not use ResultSetMetadata but will instead explicitly get the ID, NAME and BIRTHDATE column as respectively a Long, String and a Short from the underlying resultset. This also means that only these three columns will be returned, even though the query is using * and could return more than the three listed columns.

Es ist möglich, die Typeninformationen für alle oder einige der Skalare auszulassen.

sess.createSQLQuery("SELECT * FROM CATS")

 .addScalar("ID", Hibernate.LONG)
 .addScalar("NAME")
 .addScalar("BIRTHDATE")

This is essentially the same query as before, but now ResultSetMetaData is used to determine the type of NAME and BIRTHDATE, where as 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.

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.

Spalten Alias-Einspeisung wird bei der folgenden Anfrage benötigt (die aller Wahrscheinlichkeit nach fehlschlagen wird):

sess.createSQLQuery("SELECT c.*, m.*  FROM CATS c, CATS m WHERE c.MOTHER_ID = m.ID")

 .addEntity("cat", Cat.class)
 .addEntity("mother", Cat.class)

The query was intended to return two Cat instances per row: a cat and its mother. The query will, however, fail because there is a conflict of names; the instances are mapped to the same column names. Also, on some databases the returned column aliases will most likely be on the form "c.ID", "c.NAME", etc. which are not equal to the columns specified in the mappings ("ID" and "NAME").

Die folgende Form ist nicht anfällig für die Duplizierung von Spaltennamen:

sess.createSQLQuery("SELECT {cat.*}, {m.*}  FROM CATS c, CATS m WHERE c.MOTHER_ID = m.ID")

 .addEntity("cat", Cat.class)
 .addEntity("mother", Cat.class)

Diese Anfrage spezifiziert:

The {cat.*} and {mother.*} notation used above is a 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. In the following example, you retrieve Cats and their mothers from a different table (cat_log) to the one declared in the mapping metadata. You can even use the property aliases in the where clause.

String sql = "SELECT ID as {c.id}, NAME as {c.name}, " +

         "BIRTHDATE as {c.birthDate}, MOTHER_ID as {c.mother}, {mother.*} " +
         "FROM CAT_LOG c, CAT_LOG m WHERE {c.mother} = c.ID";
List loggedCats = sess.createSQLQuery(sql)
        .addEntity("cat", Cat.class)
        .addEntity("mother", Cat.class).list()

Named SQL queries can also be defined in the mapping document and called in exactly the same way as a named HQL query (see Abschnitt 11.4.1.7, „Externalisierung benannter Anfragen“). In this case, you do not need to call addEntity().



The <return-join> element is use to join associations and the <load-collection> element is used to define queries which initialize collections,


Eine benannte SQL-Anfrage kann einen Skalarwert wiedergeben. Sie müssen unter Verwendung des <return-scalar>-Elements den Spalten-Alias und den Hibernate-Typ deklarieren:


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.


You can, alternatively, use the resultset mapping information in your hbm files directly in java code.


So far we have only looked at externalizing SQL queries using Hibernate mapping files. The same concept is also available with anntations and is called named native queries. You can use @NamedNativeQuery (@NamedNativeQueries) in conjunction with @SqlResultSetMapping (@SqlResultSetMappings). Like @NamedQuery, @NamedNativeQuery and @SqlResultSetMapping can be defined at class level, but their scope is global to the application. Lets look at a view examples.

Beispiel 18.7, „Named SQL query using @NamedNativeQuery together with @SqlResultSetMapping“ shows how a resultSetMapping parameter is defined in @NamedNativeQuery. It represents the name of a defined @SqlResultSetMapping. The resultset 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. In the example 2 entities, Night and Area, are returned and each property is declared and associated to a column name, actually the column name retrieved by the query.

In Beispiel 18.8, „Implicit result set mapping“ the result set mapping is implicit. We only describe the entity class of the result set mapping. The property / column mappings is done using the entity mapping values. In this case the model property is bound to the model_txt column.

Finally, if the association to a related entity involve 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. This can be seen in Beispiel 18.9, „Using dot notation in @FieldResult for specifying associations “.



Beispiel 18.9. Using dot notation in @FieldResult for specifying associations

@Entity

@SqlResultSetMapping(name="compositekey",
        entities=@EntityResult(entityClass=SpaceShip.class,
            fields = {
                    @FieldResult(name="name", column = "name"),
                    @FieldResult(name="model", column = "model"),
                    @FieldResult(name="speed", column = "speed"),
                    @FieldResult(name="captain.firstname", column = "firstn"),
                    @FieldResult(name="captain.lastname", column = "lastn"),
                    @FieldResult(name="dimensions.length", column = "length"),
                    @FieldResult(name="dimensions.width", column = "width")
                    }),
        columns = { @ColumnResult(name = "surface"),
                    @ColumnResult(name = "volume") } )
@NamedNativeQuery(name="compositekey",
    query="select name, model, speed, lname as lastn, fname as firstn, length, width, length * width as surface from SpaceShip", 
    resultSetMapping="compositekey")
} )
public class SpaceShip {
    private String name;
    private String model;
    private double speed;
    private Captain captain;
    private Dimensions dimensions;
    @Id
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @ManyToOne(fetch= FetchType.LAZY)
    @JoinColumns( {
            @JoinColumn(name="fname", referencedColumnName = "firstname"),
            @JoinColumn(name="lname", referencedColumnName = "lastname")
            } )
    public Captain getCaptain() {
        return captain;
    }
    public void setCaptain(Captain captain) {
        this.captain = captain;
    }
    public String getModel() {
        return model;
    }
    public void setModel(String model) {
        this.model = model;
    }
    public double getSpeed() {
        return speed;
    }
    public void setSpeed(double speed) {
        this.speed = speed;
    }
    public Dimensions getDimensions() {
        return dimensions;
    }
    public void setDimensions(Dimensions dimensions) {
        this.dimensions = dimensions;
    }
}
@Entity
@IdClass(Identity.class)
public class Captain implements Serializable {
    private String firstname;
    private String lastname;
    @Id
    public String getFirstname() {
        return firstname;
    }
    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }
    @Id
    public String getLastname() {
        return lastname;
    }
    public void setLastname(String lastname) {
        this.lastname = lastname;
    }
}

Tipp

If you retrieve a single entity using the default mapping, you can specify the resultClass attribute instead of resultSetMapping:

@NamedNativeQuery(name="implicitSample", query="select * from SpaceShip", resultClass=SpaceShip.class)

public class SpaceShip {

In some of your native queries, you'll have to return scalar values, for example when building report queries. You can map them in the @SqlResultsetMapping through @ColumnResult. You actually can even mix, entities and scalar returns in the same native query (this is probably not that common though).


An other query hint specific to native queries has been introduced: org.hibernate.callable which can be true or false depending on whether the query is a stored procedure or not.

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.

Falls Ihr Mapping über einen Diskriminator verfügt, so müssen Sie <return-discriminator> verwenden, um die Diskriminator-Spalte festzulegen.

Hibernate3 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;

Um diese Anfrage in Hibernate zu verwenden, müssen Sie sie durch eine benannte Anfrage mappen.


<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.

Hibernate3 can use custom SQL for create, update, and delete operations. The SQL can be overridden at the statement level or inidividual column level. This section describes statement overrides. For columns, see Abschnitt 5.6, „Column transformers: read and write expressions“. Beispiel 18.11, „Custom CRUD via annotations“ shows how to define custom SQL operatons using annotations.


@SQLInsert, @SQLUpdate, @SQLDelete, @SQLDeleteAll respectively override the INSERT, UPDATE, DELETE, and DELETE all statement. The same can be achieved using Hibernate mapping files and the <sql-insert>, <sql-update> and <sql-delete> nodes. This can be seen in Beispiel 18.12, „Custom CRUD XML“.


If you expect to call a store procedure, be sure to set the callable attribute to true. In annotations as well as in xml.

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 annoations as well as in xml.

You can use the exact same set of annotations respectively xml nodes to override the collection related statements -see Beispiel 18.13, „Overriding SQL statements for collections using annotations“.


Tipp

The parameter order is important and is defined by the order Hibernate handles properties. You can see the expected order by enabling debug logging for the org.hibernate.persister.entity level. With this level enabled Hibernate will print out the static SQL that is used to create, update, delete etc. 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 using @org.hibernate.annotations.Table and either (or all) attributes sqlInsert, sqlUpdate, sqlDelete:


The previous example also shows that you can give a comment to a given table (primary or secondary): This comment will be used for DDL generation.

Tipp

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.

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:


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 Abschnitt 5.6, „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>

Das funktioniert sogar mit gespeicherten Prozeduren.

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>

The annotation equivalent <loader> is the @Loader annotation as seen in Beispiel 18.11, „Custom CRUD via annotations“.