JSF2：使用EJB在视图中打开会话？

Question

Does it make sense to talk about the Open Session In View Pattern within JSF2 applications? My app has JSF2 Managed Beans calling Business Service EJBs that do all the db-related stuff (there's a DAO layer but that doesn't matter right now).

Having OSIV pattern would mean that the Managed Bean would have to somehow make sure the underlying session was opened.

I am also using JPA.

Answer 1

Theoretically, the issue is exactly the same: entity will become detaches when they leave the EJB unless something keeps the scope of the EntityManager open. (Here is a great post about the topic in general: JPA implementation patterns: Lazy loading ).

From a blog post I read:

8) No Open Entity Manager In View support. [...] In EJB3, when your entity leaves bean with transaction scoped EntityManager, it is detached from persistence context and you may no longer rely on lazy loading (in fact, JPA specification does not specify the behavior in such situation, probably some vendor dependent exception will be thrown...) Of course, you may use EntityManager with extended persistence context , holding the transaction and persistence context as long as you want. But this feature is only available for SFSB, while DAO classes are typical examples of stateless services, since they only dispatch calls to the persistence layer. Additionally, having dedicated DAO bean instance for each client seems to be a big overkill.

I'm however not sure it is really true. From my understanding you should be able to write a servlet filter which uses the UserTransaction to start and commit the transaction (like the regular filter in OSIV). EJB would then participate in the transaction started in the filter and the EntityManager would remain open. I haven't tested it though, but my suggestion would be to give it a try.