how do I group by a property of a related entity in a criteria?

I'm writing a criteria that should group the results by a property of a related entity. I've tried using an alias, tried using the property path itself, but so far I get nothing. say my classes are (rough sketch):

class A{
 @ManyToOne(...)
 B b;
}
class B{
 @OneToOne(...)
 C c;
}
class C{
 String s;
}

and I want a criteria that returns the amount of A's and B's for each unique string s in C.

my initial attempt was:

session.createCriteria(A.class)
  .setProjection(Projections.projectionList()
    .add(Projections.groupProperty("b.c.s"), "string")
    .add(Projections.countDistinct("b"), "b's")
    .add(Projections.rowCount(), "a's"))

This didn't help much as b.c.s is not a property of A.

then I tried

session.createCriteria(A.class)
  .createAlias("b.c", "al")
  .setProjection(Projections.projectionList()
    .add(Projections.groupProperty("al.s"), "string")
    .add(Projections.countDistinct("b"), "b's")
    .add(Proj开发者_运维技巧ections.rowCount(), "a's"))

this actually was translated to SQL, but did not get far, as it did not include any joins in the query.

seems I am doing something wrong here.

Is it possible to get an efficient query of this kind using the criteria API?

maybe something like this:

sess.createCriteria(A.class)
    .createCriteria("b")
    .createCriteria("c")
    .setProjection(Projections.projectionList()
    .add(Projections.groupProperty("s"), "string")
    .list()
    .size()

i think you must look in double createCriteria()