Revision as of 17:19, 6 July 2011

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Key API

• [EntityManagerProperties]

Examples

• [Composite Persistence Units Example]

This page is being reviewed.

Composite Persistence Units

New in version 2.3.

Multiple persistence units with unique sets of entity types can be exposed as a single persistence context by using a composite persistence unit. A persistent unit that is part of a composite persistent unit is called a composite member persistent unit.

With composite persistence units:

• Mapping relationships can be established among any of the entities in the composite.
• The persistence context can access entities stored in different data sources.
• Queries and transactions can be performed transparently across the complete set of entities.

For example, you could persist data from a single context into different data sources, as shown below:

em.persist(new A(..));
em.persist(new Z(..));
// Insert A into database1; insert Z into database2:
// the two databases can be from different vendors.
em.flush();

Configuring Composite Persistence and Composite Member Persistence Units

As with regular persistence units, composite persistence units and their member persistence units can be configured in persistence.xml and/or by passing allowed properties to the CreateEntityManagerFactory() method of EntityManagerFactory. //REVIEWERS: Is that generic statement about using persistence.xml or CreateEntityManagerFactory correct? Does it need to be qualified in any way?// //ANDREI: I would remove it (it's been removed from the design doc )- it's confusing (also createEntityManager method is defined on Persistence interface). What I was trying to say is that composite Persistence Unit created exactly in the same way as regular persistence unit//

Certain properties must be defined on the composite persistence unit; certain properties must be defined on composite member persistence units; and other properties may be defined on either.

• The transaction type must be specified in the composite persistence unit. Transaction types of composite members are ignored.
• Data sources must be specified in composite member persistence units. Those specified in the composite are ignored.
• The eclipselink.composite-unit property must be set on the composite persistent unit.
• The eclipselink.composite-unit.member property can only be set on composite member persitent units.

The Persistence Unit Properties table and the Entity Manager Properties tables, below, show how those and other properties are processed, depending on whether they are set on the composite or on the member persistent unit.

Configuring Composite Persistent Units in persistence.xml

A minimal configuration of a composite persistent unit in persistence.xml requires the following:

• Use the eclipselink.composite-unit property to specify that it is a composite persistence unit. (Note: If this property is passed to the createEntityManagerFactory method or if it is set in system properties, it is ignored.)

• Use the <jar-file> element to specify the jar files containing the composite member persistent units. The composite persistence unit will contain all the persistence units found in the jar files specified.

For example,

...
<jar-file>member1.jar</jar-file>
<jar-file>member2.jar</jar-file>
<properties>
    <property name="eclipselink.composite-unit" value="true"/>
</properties>
...

Configuring Composite Member Persistent Units in persistence.xml

Use the eclipselink.composite-unit.member property to specify whether or not a persistent unit should be a member of a composite persistence unit:

• true specifies that the persistent unit must be a member of a composite persistence unit.

• false specifies that the persistent unit cannot be a member of a composite persistence unit (if, for example, it has dependencies on other persistence unit(s)).

For example,

...
<properties>
    <property name="eclipselink.composite-unit.member" value="true"/>
</properties>
...

The eclipselink.composite-unit.member property is not required and defaults to false if not specified. //REVIEWERS: <-- Is that statement true?// //ANDREI: Yes. "true" required only in case the persistence unit cannot be used independently (not as a composite member)//

Note: If eclipselink.composite-unit.member is passed to the createEntityManagerFactory method or if it is set in system properties, it is ignored.

//REVIEWERS: Design doc also says "If this property is set to true, the EntityManagerFactory can still be created, but it cannot be connected." I don't understand, as true is perfectly valid, no?// //ANDREI: true is perfectly valid. That means persistence unit can only be used as a member of composite - cannot be used as an independent persistence unit. Motivation: persistence unit that has dependency on classes in other persistence unit(s) - impossible to use standalone, still possible to use as a member of composite, of course the persistence unit(s) on which it depends should also be members in the same composite. Logically I would prefer to fail when the factory is created - but that would be a problem with application servers, so the next best solution is to fail on attempt to actually use the factory - createEntityManager//

Passing EntityManagerFactory Properties to Composite Member Persistent Units

While creating a composite persistent unit, EntityManagerFactory properties can be passed to composite member persistent units, as shown in the following example. The value is a map of properties, and the key is a member persistence unit's name. The map of properties is passed to that persistence unit.

//REVIEWERS: I don't completely understand this part. I have these general questions:

1. When (why) would one want to do this? That is, why do you want to use this instead of persistence.xml?
2. I think this part of the design doc (search for "While creating Composite PU EntityManagerFactory") says that you define the properties on the composite and then pass them to the members. Is that correct? But why not define them on the members directly?
3. If I got item 2, above, correct, are there times when you want to define the properties directly on the composite? directly on the members?

//REVIEWERS:

The design doc (quoting the Javadoc) says this:

"eclipselink.composite-unit.properties" -> (
   ("memberPu1" -> (   "javax.persistence.jdbc.user" -> "user1", 
                          "javax.persistence.jdbc.password" -> "password1",
                          "javax.persistence.jdbc.driver" -> "oracle.jdbc.OracleDriver",
                          "javax.persistence.jdbc.url" -> "jdbc:oracle:thin:@oracle_db_url:1521:db",
                    ) , 
   ("memberPu2" -> (   "javax.persistence.jdbc.user" -> "user2",
                          "javax.persistence.jdbc.password" -> "password2"
                          "javax.persistence.jdbc.driver" -> "com.mysql.jdbc.Driver",
                          "javax.persistence.jdbc.url" -> "jdbc:mysql://my_sql_db_url:3306/user2",
                    )

I tried to convert to code, below, but I know this isn't quite right. I think it just shows how to set the properties directly on the members (does it?). I'm not sure how to use eclipselink.composite-unit.properties itself. Please correct, as needed. // //ANDREI:With regular persistence unit user has an option to override properties specified in persistence.xml with the new ones passed to createEntityManagerFactory method. The goal is to keep the same persistence.xml, but to alter at runtime some properties - for instance connection parameters. To do the same for composite member persistence units eclipselink.composite-unit.properties is used - the value is a Map that keyed on composite member pu names, value is a Map that contains all properties to be passed to this member pu//

eclipselink.composite-unit.properties
 
Map props1 = new HashMap();
 
   props1.put(PersistenceUnitProperties.JDBC_USER, "user1");
   props1.put(PersistenceUnitProperties.JDBC_PASSWORD, "password1");
   props1.put(PersistenceUnitProperties.JDBC_DRIVER, "oracle.jdbc.OracleDriver");
   props1.put(PersistenceUnitProperties.JDBC_URL, "jdbc:oracle:thin:@oracle_db_url:1521:db");
 
Map props2 = new HashMap();
 
   props2.put(PersistenceUnitProperties.JDBC_USER, "user2");
   props2.put(PersistenceUnitProperties.JDBC_PASSWORD, "password2");
   props2.put(PersistenceUnitProperties.JDBC_DRIVER, "oracle.mysql.OracleDriver");
   props2.put(PersistenceUnitProperties.JDBC_URL, " jdbc:mysql:@oracle_sql_url:3306/user2");
 
Map memberProps = new HashMap();
   memberProps.put("memberPu1", props1);
   memberProps.put("memberPu2", props2);
 
Map props = new HashMap();
   props.put("eclipselink.composite-unit.properties", memberProps);
 
EntityManagerFactory emf = Persistence.createEntityManagerFactory("composite", props);

Examples

In the following example, the composite persistence unit compositePU specifies the transaction type and the server platform. It will contain all persistence units defined in member1.jar and member2.jar files.

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_1_0.xsd" version="1.0">
    <persistence-unit name="compositePu" transaction-type="JTA">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
 
        <jar-file>member1.jar</jar-file>
        <jar-file>member2.jar</jar-file>
 
        <properties>
            <property name="eclipselink.composite-unit" value="true"/>
            <property name="eclipselink.target-server" value="WebLogic_10"/>
        </properties>
    </persistence-unit>
</persistence>

In the following example, the composite member persistence unit memberPu1 is defined in the member1.jar file. It can be used independently as well as inside composite persistence unit.

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_1_0.xsd" version="1.0">
    <persistence-unit name="memberPu1" transaction-type="JTA">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <mapping-file>META-INF/advanced-entity-mappings1.xml</mapping-file>
        <jta-data-source>jdbc/OracleJtaDS</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="eclipselink.target-server" value="WebLogic_10"/>
            <property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.oracle.Oracle11Platform"/>
        </properties>
    </persistence-unit>
</persistence>

In the following example, the composite member persistence unit memberPu2 is defined in the member2.jar file. It has dependency on a class defined in member1.jar and cannotbe used independently.

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence persistence_1_0.xsd" version="1.0">
    <persistence-unit name="memberPu2">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <mapping-file>META-INF/advanced-entity-mappings2.xml</mapping-file>
        <jta-data-source>jdbc/MySqlJtaDS</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="eclipselink.composite-unit.member" value="true"/>
            <property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.MySQLPlatform"/>
        </properties>
    </persistence-unit>
</persistence>

Deploying and Accessing a Composite Persistence Unit

All three jars – the composite and the two members– should be deployed on the same class loader. If they are deployed to an application server, the jars should be packed in an ear file. If they run standalone, the jars should be added to the class path.

A composite persistence unit can be accessed as with any other persistence unit.

• It can be accessed using injection, for example:

@PersistenceUnit(unitName="compositePu")
EntityManagerFactory entityManagerFactory;
@PersistenceUnit(unitName="compositePu")
EntityManager entityManager;

• Or it can be created manually, using [Persistence.createEntityManagerFactory ], as shown in the following example:

EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("compositePu", properties);

Persistence Unit Properties

Persistence unit properties can be set on the EntityManagerFactory as follow:

• Composite persistence unit properties can be specified either in the composite persistence unit's persistence.xml file or passed to the its createEntityManagerFactory() method.
• Composite member persistence unit properties can either be specified in the composite member persistence unit's persistence.xml file or passed to the composite persistence unit's createEntityManagerFactory() method through the eclipselink.composite.properties property.

//REVIEWERS: Can't the properties also be passed to createEntityManager()? If so, why would you do that instead of using createEntityManagerFactory()?//

The following table shows how properties set on a composite persistence unit and its members are handled when properties are set on both. //REVIEWERS: Is that correct?// For complete PersistenceUnitProperties> reference documentation, see [|PersistenceUnitProperties].

Entity Manager Properties

Persistence unit properties can be set on the EntityManager as follow:

• Composite entity manager properties can be passed directly to the createEntityManager() method or to the setProperty method.
• Composite member properties can be passed to the same methods through the eclipselink.composite.properties property.

Limitations

Joins across tables in different data sources are not supported. This limitation affects mapping, query execution, and optimizations. For example:

• Entities mapped in different composite members cannot be joined in a query.
• If deleting an entity causes deletion from a table that is mapped by another composite member, then a "delete all" query cannot be performed. Therefore a delete all cannot be used if an entity:
  • has ElementCollection mapped in another composite member,
  • owns bidirectional relationship with a JoinTable with the target mapped in another composite member,
  • has any reference mapping that is privately owned with the target mapped in another composite member.

The inheritance hierarchy cannot be shared between different composite members.

If the target of a reference mapping is defined in a different composite member and JoinTable is used, the join table must belong to the target composite member. Such mappings must be unidirectional: the "invert" mapping cannot use mappedBy. That is because JoinTable must be defined in the same composite member with the target entity. Master mapping requires it to be in slave's member, slave mapping - in master's.You can work around this limitation by defining independent invert mapping with its own JoinTable. If you maintain both sides of the relationship, the two join tables will be in sync.

A native query created without a result class must specify the target composite member persistence unit, for example:

em.createNativeQuery("SELECT F_NAME FROM MBR2_EMPLOYEE").setHint(QueryHints.COMPOSITE_UNIT_MEMBER, "composite-advanced-member_2").getResultList();

Extensions

You can specify ElementCollection with primitive type target values with CollectionTable defined in a different composite member persistence unit, using annotations or eclipselink-orm.xml as described below:

• Annotations

@ElementCollection()
@CollectionTable(name = "MBR1_RESPONS", joinColumns=@JoinColumn(name="EMP_ID"))
@CompositeMember("composite-advanced-member_1")
@Column(name = "DESCRIPTION")
public Collection<String> getResponsibilities() {
    return responsibilities;
}

• eclipselink-orm.xml

<element-collection name="responsibilities" composite-member="xml-composite-advanced-member_3">
    <column name="DESCRIPTION"/>
    <collection-table name="XML_MBR3_RESPONS">
        <join-column name="EMP_ID"/>
    </collection-table>
</element-collection>

No @CompositeMember annotation (or composite-member attribute) is required if CollectionTable is defined in the same composite member persistence unit as the source.