Understanding EJB Persistence Services

OC4J supports the following persistence APIs:

• TopLink EJB 3.0 JPA persistence provider (see "How Does OC4J Manage Persistence in an EJB 3.0 Application?")

• TopLink EJB 2.1 persistence manager (see "How Does OC4J Manage Persistence in an EJB 2.1 Application?")

• Orion EJB 2.0 persistence manager (deprecated: see the Oracle Containers for J2EE Orion CMP Developer's Guide)

OC4J chooses the type of persistence to use based on the type of object-relational mappings you define and the presence or absence of certain deployment XML files. How OC4J chooses depends on the type of EJB application you are deploying:

• EJB 3.0 Applications

• EJB 2.n Applications

EJB 3.0 Applications

OC4J uses the TopLink EJB 3.0 JPA persistence provider if you deploy EJB 3.0 entities in an ejb.jar file without an ejb-jar.xml file, or if OC4J detects one or more EJB 3.0 annotations.

For more information, see the following:

• "How do You Define an EJB 3.0 Application?"

• "Customizing the JPA Persistence Provider"

EJB 2.n Applications

For EJB 2.1 and EJB 2.0 applications, OC4J uses the algorithm that Table 2-4 summarizes by your action. For example, if you deploy a CMP application without a toplink-ejb-jar.xml file, OC4J uses the TopLink persistence manager and creates default TopLink object-relational mappings.

Table 2-4 OC4J EJB 2.n Persistence Manager Selection

Your Action	toplink-ejb-jar.xml	orion-ejb-jar.xml	Persistence Manager	Mapping Type
Deploy.	Absent	Optional; if present, contains no mappings and no persistence-manager element.	Toplink	Default TopLink
Deploy.	Present	Optional; if present, contains no mappings and no persistence-manager element.	Toplink	TopLink as defined in toplink-ejb-jar.xml (default persistence manager properties)
Edit the orion-ejb-jar.xml file to set persistence-manager element name attribute to toplinkFoot 1 . Edit additional persistence-manager subentriesFootref 1. Deploy.	Present	Optional; if present, contains no mappings	Toplink	TopLink as defined in toplink-ejb-jar.xml (custom persistence manager properties)
Deploy.	Absent	Present and contains Orion mappings; persistence-manager element is optional.	Orion	Orion as defined in orion-ejb-jar.xml
Edit the orion-ejb-jar.xml file to set persistence-manager element name attribute to orionFootref 1. Deploy.	Absent	Optional; if present, contains no mappings	Orion	Default Orion

^Footnote 1 See "<persistence-manager>".

For more information, see the following:

• "How do you Define an EJB 2.1 Module?"

• "Customizing the TopLink EJB 2.1 Persistence Manager"