Question

I’m using JPA (not JDO) on Google App Engine and this is a typical example of my service method:

@Autowired
EntityManagerFactory entityManagerFactory;

public Collection<Message> getAll() {
    EntityManager em = entityManagerFactory.createEntityManager();
    Collection<Message> result = null;

    try {
        Query query = em.createQuery("SELECT e FROM Message e");
        result =  query.getResultList();
        //The workaround
        //if(result != null) result.size();
    } finally {
        em.close();
    }

    return result;
}   

When I try to use the collection outside the method I get the “famous” error reporting that the object manager is closed. Calling the size() method is a workaround, but I dislike this kind of “dirty” solution. I wonder there isn’t any method to have this collection detached or lazy loading disabled.

Answer 1

I don’t know if it is “clean”, but a frequently recommended approach is to have a servlet filter that creates a thread-local EntityManager before your code runs and closes it at the very end.