Question

I’m building a web app using Seam, using stateful session EJBs as business components (also annotated as Seam components). In this scenario what’s the best practice for injecting the entity manager, using @In or @PersistenceContext? will one of the two options cause me problems? (assume the duration of a conversation and its associated persistence context is not an issue)

If I choose to use @In and need to mark a method as non-transactional, should I use @Transactional(TransactionPropagationType.SUPPORTS) or @TransactionAttribute(TransactionAttributeType.SUPPORTS)?

Answer 1

You are not going to have any issue using Seam managed persistence context instead of the standard container managed persistence context, so in my opinion the best practice is using @In.
Among the advantages of using a Seam managed persistence context there are:

• You can inject the same persistence context in non-EJB Seam component
• Use of <s:convertEntity> in the view (assuming you are going to use JSF)
• Use of EL in the Query Language
• You have the persistence context bound to the conversation context (not important for you, if understand correct)

If you choose @In, thus Seam managed persistence context, then you can have declarative transaction demarcation using @Transactional in non-EJB Seam component where @TransactionAttribute make no sense.
For EJB session bean annotated as Seam component (@Name) @TransactionAttribute should be used with the same semantic as defined for EJB3.

Since @Transactional doesn’t have a REQUIRES_NEW value the following applies as explained in the reference documentation:

If you are using EJB3 and mark your class or method @TransactionAttribute(REQUIRES_NEW)
then the transaction and persistence context shouldn’t be propagated to method calls on this
object. However as the Seam-managed persistence context is propagated to any component
within the conversation, it will be propagated to methods marked REQUIRES_NEW. Therefore,
if you mark a method REQUIRES_NEW then you should access the entity manager using
@PersistenceContext.

Chapter 9 of Dan Allen book Seam In Action will satisfy any doubt on this topic.