when to use detached criteria in hibernate?

Question

when to use detached criteria? and what is the advantage we get by using detached criterias instead of normal criteria?

Criteria criteria = sessionFactory.getCurrentSession().createCriteria(Some.class);


DetachedCriteria criteria = DetachedCriteria.forClass(Some.class);

Thanks!

Answer 1

As per docs

Some applications need to create criteria queries in "detached mode", where the Hibernate session is not available. This class may be instantiated anywhere, and then a Criteria may be obtained by passing a session to getExecutableCriteria(). All methods have the same semantics and behavior as the corresponding methods of the Criteria interface.

Answer 2

'Detached from session object'

Detached Criteria may be used in two scenarios:

1. Building criteria query with no session object:
   Session only requires during executing the query/submitting the query to database, not while building the query.

   Ex:

       DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Department.class);
       detachedCriteria.add(Restrictions.eq("DEPTID", 1));
       ProjectionList projectionList = Projections.projectionList();
       projectionList.add(Projections.property("DEPTID"));
       detachedCriteria.setProjection(projectionList);
   
      //Add more
       .............................
   

   In the above code do you find any necessity of having session object for building such a criteria query? absolutely NO.

2. Building same criteria query for multiple times:
   Build it once irrespective of the session object, and can be used whenever/wherever you want.

Finally when session object is available, use the above query with session as follows:

detachedCriteria.getExecutableCriteria(session).list();