JSF application backend architecture with JPA and CDI - jsf

Question

I'm working on a JSF application with JPA and CDI; I use the following backend architecture:
Controllers (CDI annotation for JSF process)
Services (CDI annotations to be injected into Controllers and other Services)
DAOs (handled with EntityManager)
My question is, how should exactly be EntityManager and transactions be handled?
For example transactions (I don't use EJB or Deltaspike, so no declarative transactions available) should be managed by the Service layer (am I right?), but each data-releated other operation should be handled by the DAOs. So where should EntityManager be injected?
Also, should EntityManager be request (or session or method) scoped?
Thanks,
krisy

Answer 1

I would use service layer to manage a business logic and data access layer to manage object-relational model. As a consequence of the above, entity manager and transactions should be part of DAO. It's important to keep transactions as short as possible.
The decision which type of scope to choose is not so obvious as it depends on the nature of your bean/application. An example usage followed by this presentation, slide #15:
#RequestScoped: DTO/Models, JSF backing beans
#ConversationScoped: multi-step workflow, Shopping cart
#SessionScoped: User login credentials
#ApplicationScoped: Data shared by entire app, Cache
As you can see a scope of a given bean and the related entity manager is specific for the problem it concerns. If a given bean is request scoped its state is preserved for a single HTTP request in the same HTTP session. For a session scoped bean the state is maintained through HTTP session. An example approach may look somehow like the following (pseudocode):
#SessionScoped // conversation, application scoped as well
public class ServiceImpl implements Service {
#Inject
private Dao dao;
public void createSomething(SomeDto dto) {
// dto -> entity transformation
dao.create(entity);
}
public SomeDto getSomething(int id) {
SomeEntity entity = em.findById(id);
// entity -> dto transformation
return dto;
}
}
#RequestScoped
#Transactional
public class DaoImpl implements Dao {
#Inject
private EntityManager em; //creating em is cheap
// TxType.REQUIRED by default
public void create(SomeEntity entity) {
em.persist(entity);
}
#Transactional(TxType.NOT_SUPPORTED)
public SomeEntity findById(int id) {
return em.find(SomeEntity.class, id);
}
}