Can I get a reference from a JPA bean to the EntityManager instance that manages it?

The question basically sums it up.

Play framework has the JPABase cl开发者_如何学JAVAass that JPA beans inherit from. This class has a method called em() which returns the bean's entityManager instance. Is there something equivalent to this in plain JPA?

AFAIK, no. And I would find it very questionable. JPA entities are supposed to be POJOs usable outside of the persistence layer, where the JPA classes are not even in the classpath. Exposing the EntityManager in those POJOs seems wrong to me.

It looks like the Play Framework implements the Active Record pattern allowing you to make persistence operations directly in the bean. This is perfectly acceptable and you can implement a similar solution.

However, once you choose this approach, you will not have the benefits of POJOs. For example, this solution may not be the best alternative if your application has n-tier architecture.

Anyway take a look at the source code, it's free! https://github.com/playframework/play/blob/master/framework/src/play/db/jpa/JPABase.java