在MVP / MVC架构中使用有状态Bean作为演示者/控制器是一个好主意吗？

Question

I'd like a controller that is able to seamlessy access the persistence layer and EJB is a nice technology for this purpose. I can do something like this:

@PersistenceContext
EntityManager em;

...    

Cat timmy = em.findById(Cat.class, "Timmy");
timmy.color = "red";

And it feels like timmy is in-memory. The sad part is that this has to be done at business level because beans are only at business level. However transactions should be defined at client level in the MVP. That's why I would like to have a Presenter that is a @Stateful bean. This way I can start and end transactions at client level. Anyways I have this strange feeling that @Stateful bean are evil and I'd rather not use them.

Answer 1

is that:

@PersistenceContext
EntityManager em;

...

Cat timmy = em.findById(Cat.class, "Timmy");
timmy.setColor("red");
em.merge(timmy);

working?

in term of architecture I use @Stateless Dao

@Stateless
public class CatDao extends Dao<Cat> {
    public CatDao () {
        super(Cat.class);
    }
}

public class Dao<E> {

    @PersistenceContext(unitName = "myappPU")
    private EntityManager em;

    private final Class<E> entityClass;

    protected Dao(Class<E> entityClass) {
        this.entityClass = entityClass;
    }

    public E find(Object id) {
        return em.find(entityClass, id);
    }

    public List<E> findAll() {
        CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
        cq.select(cq.from(entityClass));
        Query q = entityManager.createQuery(cq) ;
        return q.getResultList();
    }

    public void create(E entity) {
        em.persist(entity);
    }

    public void edit(E entity) {
        em.merge(entity);
    }

    public void remove(E entity) {
        em.remove(entityManager.merge(entity));
    }
}

so in the controller I do

    @Inject
    private CatDao dao;

    //...

    Cat cat = dao.find("Timmy");
    cat.setColor("red");
    dao.edit(cat);

see... statless

Netbeans generate this Dao automatically but called them Facade (new>Other>Entreprise JavaBeans>session beans for entity classes)

Answer 2

Finally I did it! The solution was hidden in CDI specs:

@Inject CatRepository catRepository;

 @Transactional
 void changeColorToCat(String color, String catName) {
    Cat timmy = catRepository.findByName("Timmy");
    timmy.color = "red";
 }

And it's done! It's like databases don't exist at all!