How to refer to a subclass specific field in a CriteriaQuery where the super class is queried?

Question

I\'m trying to achieve something like the following, using the JPA Criteria API:

SELECT b FROM Box b JOIN SpecialItem s WHERE s.specialAttr = :specialAttr
         


        

Answer 1

If using JPA 2.1 you might use

"SELECT b FROM Box b WHERE TREAT(b.item as SpecialItem).specialAttr = :specialAttr"

or

CriteriaQuery q = cb.createQuery(Box.class);
Root box= q.from(Box.class);
Join order = box.join("item");
q.where(cb.equal(cb.treat(order, SpecialItem.class).get("specialAttr"),
    qb.parameter(String.class, "specialAttr")));
q.select(Box);