[seam-dev] Transactions and persistence

[Stuart Douglas]

As some of you may know I've started looking at the transactions and persistence module. To start with I am just going to port what we had in seam 2, and we can work form there. I have already ported the UserTransaction wrapper stuff and the transaction interceptor. Alternate UserTransaction wrappers can be specified in seam XML (e.g. if you want to use HibernateTransaction).

I have changed the default to use EJB synchronisations (<transaction:ejb-transaction/> from seam 2), you will need to manually install SeSynchronisations in a non EJB environment.  I will look at making the extension smart enough to detect this in most cases, so it will just work either way. 
 
I think that in a normal EE6 setup this module should not require a single line of XML, configuration should only be required if you are in a non-EE environment. 

I that the SMPC should be configured with an annotation on a producer field, something like:

@Produces
@ManagedPersistenceContext
@PersistenceContext
@ConversationScoped
EntityManager entityManager;

I don't think we should override the behaviour of every resource producer field by default, and xml configuration should also be supported. 

Questions:

Do we want to allow @TransactionAttribute to be used on managed beans (as well as @Transactional)?

I think we should do this. Also there was talk of changing the names used in the seam provided annotation, is that still on the cards (personally I am very much against this)? 

Are we still going to provide seam equivalents of the EE API's (e.g. @ApplicationException etc)? 

I'm guessing yes.

Seam 2 allowed you to use seam-jndi.properties to specify JNDI properties

Are we going to do something like this? If so where at. 

Are we going to support REQUIRES_NEW for managed beans?

I really want this. It will probably only be availible in a JTA environment though, and will probably require XML configuration in some cases.

Are we going to stop the ManagedPersistenceContext from propagating across the transaction boundary for REQUIRES_NEW transactions?

I think that in this situation:

@Stateless
public class MyEJB
{
  @Inject EntityManager entityManager;

  @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
  public void doStuff()
  {
	entityManager.createQuery(...);
       ...	
  }
}

we should inject a new EM rather than one that is enlisted in the outside transaction. We could also provide a TransactionScoped em, but that does not solve the problem in the following situation:

@Stateless
public class MyEJB
{
  @Inject HelperBean helper;

  @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
  public void doStuff()
  {
	helper.doStuff()
  }
}

public class HelperBean {

  @Inject EntityManager entityManager;
  public void doStuff() {};
}

I think that we should maintain a stack of EM's in the Managed Persistence Context, and push a new one when we cross a transaction boundary, so all em calls after than point are invoked on a new EM. This is a real problem, and there are heaps of posts about this in the seam 2 forum.

Where do seam managed transactions belong?

Probably the faces module. 

Do we want to support multiple RESOURCE_LOCAL transactions?

There have been quite a few posts on the forum about this, but I don't know if it really makes sense. You would need some way of telling the transaction interceptor which UT it is supposed to use. Seam managed transaction would probably have to work on both transactions, wether they are needed or not. 

Does all this sound ok? If so I will write this stuff up on the module page and start implementing.

Stuart



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