static access to entity manager in spring and unusual architecture

Question

quick question:

I have webapplication (wicket+spring+jpa) and was thinking about rather unusual architecture design. Please check it out and give your comments.

Answer 1

The EntityManager is stateful (in a way). The factory is stateless. And having a static entity manager is an anti-pattern called "session per application" (or entity manager per application).

Note that these are implementation details - how is @PersistenceContext EntityManager em handled. Hibernate provides EntityManagerImpl which creates a new hibernate session if one isn't already created. But if it is already created, it holds a reference to it (the session=persistence context).

Having a static entity manager means it is not container-managed. Which in turn means that you are responsible for managing the persistence context.

What you are trying to do is Domain-driven design. Here is an article of mine about DDD and JPA.

My personal preference is not to go that way - the object should not be able to persist itself in a database - this is infrastructure logic. In order to avoid code duplication you can simply have a BaseDao which wraps the persist method. Or even directly use the EntityManager in your service layer. (This assumes you have clear layer boundaries)

If you are really sure you want to go the DDD path, take a look at the examples in the article. Spring allows you to inject the entity manager in any object, via aspectJ. So your entity manager will be properly handled, as well as your transactions.