Select Entity where Hibernate OneToOne association is not present

Question

I have two classes with a bi-directional @OneToOne mapping to each other.

Class A {
@OneToOne(fetch = FetchType.Lazy, mappedBy="a")
private B b;
}

Class B {
@OneToOne(fetch = FetchType.Eager)
private A a;
}

I need to write code to retrieve all instance of B which to do not have an instance of A associated with them. I also need to write a similar query for all A which have no B.

I have tried:

Criteria criteria = getSession().createCriteria(B.class)
criteria.add(Restrictions.isNull("a")

but this seems to always return null. Thoughts?

Answer 1

This should work, for both directions:

Criteria criteria = session.createCriteria(B.class, "b");
criteria.createAlias("b.a", "a", Criteria.LEFT_JOIN);
criteria.add(Restrictions.isNull("a.id"));

Answer 2

There is a documented problem in Hibernate, which says that "The query language IS NULL syntax won't work with a one-to-one association!"

Also, there is a pending Jira on the same issue JIRA

Till this gets fixed, the workaround provided by JB Nizet works great.