Hibernate criteria: Joining table without a mapped association

Question

I'd like to use Hibernate's criteria api to formulate a particular query that joins two entities. Let's say I have two entities, Pet and Owner with a owner having many pets, but crucially that association is not mapped in the Java annotations or xml.

With hql, I could select owners that have a pet called 'fido' by specifying the join in the query (rather than adding a set of pets to the owner class).

Can the same be done using hibernate criteria? If so how?

Thanks, J

Answer 1

My understanding is that if you do this using HQL, you are creating a Cartesian join with a filter, rather than an inner join. Criteria queries do not support doing this.

Answer 2

This is indeed possible with criteria:

DetachedCriteria ownerCriteria = DetachedCriteria.forClass(Owner.class);
ownerCriteria.setProjection(Property.forName("id"));
ownerCriteria.add(Restrictions.eq("ownername", "bob"));

Criteria criteria = getSession().createCriteria(Pet.class);
criteria.add(Property.forName("ownerId").in(ownerCriteria));

Update: This actually performs a sub-query instead of a join but it allows you to use Criteria on two entities that do not have a hibernate relationship defined.

Answer 3

In NHibernate you can use subqueries which are defined as DetachedCriteria. Not sure if it works the same in Java, most probably it is the same:

DetachedCriteria pets = DetachedCriteria.For<Pet>("pet")
  .SetProjection(Projections.Property("pet.ownername"))
  .Add(/* some filters */ );

session.CreateCriteria(typeof(Owner))
  .Add(Subqueries.PropertyIn("name", pets);

Assumed that it is joined using the name of the owner.

Answer 4

Criterion ownerCriterion = Restrictions.sqlRestriction(SELECT ownerId FROM   Owner WHERE ownerName ='bob');
Criteria criteria = getSession().createCriteria(Pet.class);
criteria.createCriteria("ownerId").add(ownerCriterion);

Answer 5

There's a SQLCriterion, which you can give arbitrary SQL, and add to your Criteria. In the SQL string, the token {alias} "will be replaced by the alias of the root entity."