Customize an EntityManager

Question

I require adding a little intelligence to the JPA EntityManager, customizing the createNamedQuery. I'm working in a project build of many modules, where every module annotates its instance of EntityManager with @PersistenceContext(unitName = "emModuleName").

It seems that I cannot simply extends the interface EntityManager, but I don't find any documentation about this matter online.

Does anyone has an idea what is the best solution for my needs?

I cannot extend one specific implementation because the application has to be JPA implementation independent. Thanks

Since each JPA provider IMPLEMENTS EntityManager with their own class, and since you say you cannot extend an implementation, then you cannot do that. — Neil Stockton
– Neil Stockton, Commented Nov 9, 2016 at 15:04

Antoniossss · Accepted Answer · 2016-11-09 15:03:41Z

1

One way would be to create own implementation of EntityManager that would act as a wrapper to real EnityManager. Intercept required method (in your case createNamedQuery), and delegate every other call to underyling object.

OR

Create your own proxies to intercept method calls.

Both ways however are not that trivial to use as you probably would like it to be.

answered Nov 9, 2016 at 15:03

Antoniossss

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sahoora · Accepted Answer · 2016-11-10 14:33:06Z

You can create a BaseEntitymanager which provides a base implementation for basic CRUD services and the respective DAO has to extend the BaseEntityManager.

BaseEntityManager:

public interface EntityManagerBase<E, K> {
    E create(E entity);
    void delete(E entity);
    E update(E entity);
}

EntityManagerBaseImpl

    public abstract class EntityManagerBaseImpl<E, K> implements
        EntityManagerBase<E, K> {

    private EntityManager entityManager;

    private TransactionManager txManager;

    private Class<E> type;

    public E create(E entity) {     
        entityManager.persist(entity);
        entityManager.flush();
        return entity;
    }

MyDaoImpl:

public class MyDaoImpl extends EntityManagerBaseImpl<MyDBO, Long> implements MyDao {
//put your implementation of methods
}

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