I have a problem with a set of objects in a hbm file. I have a table with students that has fk to table schools. Other table with classes that has a FK to schools. So in the hbm of schools I have a set of classes. Imagine that I want to get the students that study in the school x and study in the class x.
The problems is that I cannot do this:

From the table students I do:

filter.addCriterion("school", objectSchool)//fk
filter.addAlias("schools", "schools");
filter.addAlias("schools.classes", "class");
filter.addCriterion(Restrictions.eq("class.classId", new Integer(id)));

But the sql is not correct, I mean , I get all the students from the school objectSchool and not only the student from the class x. My question is:

How to resolve this with Criterions and not with HQL.

Thanks