Persistence Unit as Resource_Local or Jta

Persistence unit as RESOURCE_LOCAL or JTA?

JPA implementations have the choice of managing transactions themselves (RESOURCE_LOCAL), or having them managed by the application server's JTA implementation.

In most cases, RESOURCE_LOCAL is fine. This would use basic JDBC-level transactions. The downside is that the transaction is local to the JPA persistence unit, so if you want a transaction that spans multiple persistence units (or other databases), then RESOURCE_LOCAL may not be good enough.

JTA is also used for managing transactions across systems like JMS and JCA, but that's fairly exotic usage for most of us.

To use JTA, you need support for it in your application server, and also support from the JDBC driver.

persistence.xml different transaction-type attributes

Defaults

Default to JTA in a JavaEE environment and to RESOURCE_LOCAL in a JavaSE environment.

RESOURCE_LOCAL

With <persistence-unit transaction-type="RESOURCE_LOCAL"> you are responsible for EntityManager (PersistenceContext/Cache) creating and tracking

• You must use the EntityManagerFactory to get an EntityManager
• The resulting EntityManager instance is a PersistenceContext/Cache
  An EntityManagerFactory can be injected via the @PersistenceUnit annotation only (not @PersistenceContext)
• You are not allowed to use @PersistenceContext to refer to a unit of type RESOURCE_LOCAL
• You must use the EntityTransaction API to begin/commit around every call to your EntityManger
• Calling entityManagerFactory.createEntityManager() twice results in two separate EntityManager instances and therefor two separate PersistenceContexts/Caches.
• It is almost never a good idea to have more than one instance of an EntityManager in use (don't create a second one unless you've destroyed the first)

JTA

With <persistence-unit transaction-type="JTA"> the container will do EntityManager (PersistenceContext/Cache) creating and tracking.

• You cannot use the EntityManagerFactory to get an EntityManager
• You can only get an EntityManager supplied by the container
• An EntityManager can be injected via the @PersistenceContext annotation only (not @PersistenceUnit)
• You are not allowed to use @PersistenceUnit to refer to a unit of type JTA
• The EntityManager given by the container is a reference to the PersistenceContext/Cache associated with a JTA Transaction.
• If no JTA transaction is in progress, the EntityManager cannot be used because there is no PersistenceContext/Cache.
• Everyone with an EntityManager reference to the same unit in the same transaction will automatically have a reference to the same PersistenceContext/Cache
• The PersistenceContext/Cache is flushed and cleared at JTA commit time

ResourceLocal to JTA

I finally was able to fix my problem. From my searches it resulted that you can not use EntityManager when you are using JTA within ManagedBeans for example. However it can be used in a stateless bean and then we can inject this Stateless Bean to the ManagedBean and use its methods. The procedure is as follows:

• create an EJB (a simple class with @Stateless annotation)

• move the method that uses EntityManager to the EJB

• inject the EJB into your managed bean (using @EJB annotation) and call the relevant method

For more information refer to this other post: JTA & MySQL

Cannot inject RESOURCE_LOCAL container managed EntityManager using @PersistenceContext

JTA : In Java EE environment, transactions are managed by the container & by default its JTA transaction. You can get entity manager by lookup or injection.

RESOURCE_LOCAL : In Java SE, application have to manage transactions explicitly & resource local transactions are native transactions. You have to create EntityManagerFactory & then can create entity manager from it.

As you are deploying it in application server, change the transaction-type to JTA in persistence.xml.

What properties does persistence-unit have in apache openjpa?

This is reference for persistence properties for JPA 2.X:
https://www.developer.com/java/ent/standard-persistence-properties-in-jpa-2.html

This is reference for openjpa: https://openjpa.apache.org/builds/3.0.0/apache-openjpa/docs/ref_guide_conf_openjpa.html

And here are also properties for Hibernate and EclipseLink: Properties reference for hibernate in persistence.xml

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