Question

I have a generic DAO class that looks like this:

public class GenericDaoJpa <T extends DomainObject> implements GenericDao<T> {

    private final Class<T> type;

    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
    protected EntityManager entityManager;

    public GenericDaoJpa(Class<T> type) {
        super();
        this.type = type;
    }

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    public T get(Object id) {
        return (T) entityManager.find(type, id);
    }
}

The implementation DAO class looks like this:

    @Repository("appDao")
    public class ProductDaoJpa extends GenericDaoJpa<Product> implements ProductDao{

    public ProductDaoJpa() {
        super(Product.class);
    }

    public List<Product> getAllProducts() {
        return getAll();
    }   
}

I have configured another persistentUnit called mySecondPersistenceUnit for a different database. I would like to create a new DAO class that will also extend the GenericDaoJpa class but use a different persistent unit. How can i extend the GenericDaoJpa class but use a different persisitent unit for each DAO?

I tried moving this declaration to each of the DAO classes but this causes the parent class not to compile because it has no reference to the entityManager.

@PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
protected EntityManager entityManager;

Answer 1

Try to use method injection instead:

public class GenericDaoJpa <T extends DomainObject> implements GenericDao<T> {

    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}

While child class that need use different PU:

@Repository("appDao")
public class ProductDaoJpa extends GenericDaoJpa<Product> implements ProductDao{

    @Override
    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="mySecondPersistenceUnit")
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}