EclipseLink/Examples/JPA/Composite

EclipseLink JPA: Composite Persistence Units Example

Starting with EclipseLink 2.3.0 JPA developers can now combine persistence units together at runtime allowing entities to be stored in different databases. This includes support for relationships between entities in different persistence units (references across databases). For long time users of TopLink/EclipseLink this feature is an upgrade to the native Session Broker functionality to make it easier to use with JPA.

Usage

• Two or more persistence units could be combined into a single Composite persistence Unit.
• Each composite members persistence unit keeps mapping its classes to its own database.
  • Therefore Composite persistence unit allows to map different entities to different data bases.

Basic Composition Example

Below is an example of Composite persistence unit definition. This example assumes two persistence units composed into a single parent unit. In this simple case, there are no relationships between the two units. The parent Persistence Unit 'compositePu' specifies transaction type and server platform, contains a property to define it as the parent PU. It 'contains' 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>

• memberPu1 defined in member1.jar file. As it contains no relationships to other PUs, it can be used independently as well as inside composite persistence unit. (Note, this pu is mapped to an Oracle DB)

<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>
        <jta-data-source>jdbc/OracleJtaDS</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.oracle.Oracle11Platform"/>
        </properties>
    </persistence-unit>
</persistence>

• memberPu2 defined in member2.jar file. As with memberPu1, it can be used independently as well as inside composite persistence unit. (Note, this pu is mapped to MySql DB)

<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>
        <jta-data-source>jdbc/MySqlJtaDS</jta-data-source>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.oracle.MySqlPlatform"/>
        </properties>
    </persistence-unit>
</persistence>

For more information about Composite persistence units please see the design doc.

Relationship Example