Using injected EntityManager in class hierarchies

Question

The following code works:

@Stateless
@LocalBean
public class MyClass 
{
       @PersistenceContext(name = "MyPU")
       EntityManager em;


       public void myBusinessMethod(MyEntity e)
       {
          em.persist(e);
       }
 }

But the following hierarchy gives a TransactionRequiredException in Glassfish 3.0 (and standard JPA annotations with EclipseLink.) at the line of persist.

 @Stateless
 @LocalBean
public class MyClass extends MyBaseClass
{
       public void myBusinessMethod(MyEntity e)
       {
          super.update(e);
       }
 }



public abstract class MyBaseClass
{
       @PersistenceContext(name = "MyPU")
       EntityManager em;

       public void update(Object e)
       {
          em.persist(e);
       }
 }   

For my EJB's I collected common code in an abstract class for cleaner code. (update also saves who did the operation and when, all my entities implement an interface.)

This problem is not fatal, I can simply copy update and sister methods to subclasses but I would like to keep all of them together in a single place.

I didn't try but this may be because my base class is abstract, but I would like to learn a proper method for such a (IMHO common) use case.

Answer 1

Your approach isn't wrong (if it works)

However it is more common to either use (inject) a Dao and call methods on it, or if the Dao is a redundant layer that only wraps the EntityManager, you can simply call the methods on EntityManager directly. Of course, exposing the EntityManager to subclasses via a protected getter.

getEntityManager().persist(e);

Answer 2

The problem was not using superclass' injected entity manager, but calling another EJB's method: e.g.

@Stateless
@LocalBean
public class MyBean extends MySuperBean
{
  @EJB
  com.example.project.MyOtherBean otherBean;

  public boolean myService(String userName, MyEntity entity)
  {
     if(otherBean.checkAuthority(userName))
     { 
        super.insert(entity);
     }
   }
 }

I was using this pattern when OtherBean was not a bean and checkAuthority was a static method using (non-JTA) EntityManagerFactory. Then I changed OtherBean to extend MySuperBean too. I think, in this case, when OtherBean ends checkAuthority, JTA ends the transaction and MySuperBean's insert can't find a transaction to persist entity. Understandably Stateless EJB's don't let fellow EJB's to proceed the transaction.

As Pascal, I initially thought that injection does not work with inheritance but this problem continued when I directly called em.persist() in the subclass. After this I finally was able to check other possible causes.

Thanks for all the input.