Revision as of 14:02, 3 July 2011

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Key API

• @VirtualAccessMethods

Examples

• Extensible Entities

******SANDBOX VERSION******

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. The single context can access entities stored in different data sources, so mapping relationships can be established between them, and 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 db1; insert Z into db2:
// the two different databases can be from different vendors
em.flush();

A persistent unit that is part of a composite persistent unit is called a composite member persistent unit.

Configuring Composite Persistence Units

You can configure composite persistence units in persistence.xml or in the EntityManagerFactory.

Configuration in persistence.xml

Configure a composite persistent unit in persistence.xml, as follows:

• Use the eclipselink.composite-unit property to indicate that it is a composite persistence unit. This property passed to the createEntityManagerFactory method or in system properties is ignored////?/////.
• Use <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>
...

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.

For example,

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

Configuration in EntityManagerFactory

The property passed to the createEntityManagerFactory method or in system properties is ignored.

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, the key is a member persistence unit's name,

• the value is a map of properties to be passed to this persistence unit.

"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",
                    )

• The transaction type should be specified in the composite persistence unit. Transaction types of composite members are ignored.
• Data sources should be specified in composite member persistence units. Those specified in the composite are ignored.

Example

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 could 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 can't be 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], as shown in the following example:

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

Persistence Unit Properties

• Composite Persistence Unit property could be specified either in its persistence.xml or passed to createEntityManagerFactory method;
• Composite member Persistence Unit property could be either specified in its persistence.xml or passed to composite's createEntityManagerFactory through "eclipselink.composite.properties" property.

Entity Manager Properties

• Composite Entity Manager property could be directly passed to createEntityManager method or setProperty method
• Composite member property could be passed to the same methods through "eclipselink.composite.properties" property.

Limitations

• Main limitations' cause is that tables in different data bases cannot be joined in a query. Examples:
  • Entities mapped in different composite members could not be joined in a query.
  • If deletion of an entity causes deletion from a table that is mapped by another composite member then delete all query can't be performed.
    • Therefore delete all cannot be used if an entity
      • has ElementCollection mapped in another composite member,
      • owns bidirectional relationship with a JoinTable with target mapped in another composite member,
      • has any reference mapping that is privately owned with target mapped in another composite member.
• Inheritance hierarchy cannot be shared between different composite members.
• If target of a reference mapping is defined in a different composite member and JoinTable is used, then the join table must belong to the target composite member.
  • Such mappings must be unidirectional - the "invert" mapping cannot use "mappedBy".
    • That's because JoinTable must be defined in the same composite member with target entity: master mapping requires it to be in slave's member, slave mapping - in master's.
  • Workaround is to define independent invert mapping with its own JoinTable.
    • If user maintains both sides of the relationship then the two join tables will be in sync.
• Native query created without result class must specify the target composite member persistence unit.

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

Extensions

• User can specify ElementCollection with primitive type target values with CollectionTable defined in a different composite member persistence unit using
  • 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.

Documentation

Open Issues

This section lists the open issues that are still pending that must be decided prior to fully implementing this project's requirements.

Decisions

This section lists decisions made. These are intended to document the resolution of open issues or constraints added to the project that are important.