With a DAO pattern, do you ever expose the EntityManager or Session as a parameter?

Question

Is there ever a case in a standard webapp where one would pass an EntityManager or Session as a parameter to a DAO call, i.e. findPersonByName(String name, Session session)? Or should the the opening and closing of the session be abstracted in the implementation?

Answer 1

No, it should never be used, but a Service layer might. Imagine you have two different methods (in possibly different DAO's) that need to be encapsulated in the same transaction (commit/rollback), than you might want/have to use the same connection object.

Answer 2

No, neither the DAO nor the service layers should know or care about session. Services ought to be idempotent. The session is an view/controller artifact; let the controller manage it.

Answer 3

A better approach would be to initialize or otherwise inject the DAO with the SessionFactory. Then you can do things like this:

public abstract class AbstractHibernateDao<T extends Object>
    implements AbstractDao<T> {

    private SessionFactory sessionFactory;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    protected Session getSession() {
        return sessionFactory.getCurrentSession();
    }

    public void save(T t) { getSession().save(t); }

    public void update(T t) { getSession().update(t); }

    ...
}

without having to pass Sessions all over the place.