JBossDeveloper

This should work :

   @Inject @MyDB private EntityManager db;
   @Resource private UserTransaction ut;

   ...

   ut.begin();
   db.joinTransaction();
   db.persist(myEntity);
   db.flush();
   ut.commit();

Not sure that flush is mandatory.

Sorry @Resource should be :

@Resource(mappedName="java:comp/UserTransaction") 
private UserTransaction ut;

Don't know why the mappedName is necessary, but it works in both JBoss 6 and GF 3.

According to the spec (3.6) @Inject UserTransaction should work. If it doesn't, that's a bug.

Right, this works perfectly (in JB6 at least) :

  @Inject @MyDB private EntityManager db;
  @Inject private UserTransaction ut;

  ...

  ut.begin();
  db.joinTransaction();
  db.persist(myEntity);
  db.flush();
  ut.commit();