Polymorphic CriteriaQuery without inverse relationship

Question

I have the following EJB structure. Don\'t wonder about Animal and Inventory, these classes are only here to demonstrate the structure in a simplified

Answer 1

If you are using EclipseLink, solution is simple. Modify the Path criteria to cast to RfIdTag:

Path<Object> path = ((Path) from.join("idTag").as(RfIdTag.class)).get("code");

If you are using Hibernate, replace your method with:

public static <T extends ItemWithIdTag> T fOwner(Class<T> type, String catName) {
    CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
    CriteriaQuery<T> criteriaQuery = criteriaBuilder.createQuery(type);
    Root<T> fromType = criteriaQuery.from(type);
    Root<RfIdTag> fromRfId = criteriaQuery.from(RfIdTag.class);

    Path<Object> pathCode = fromRfId.get("code");
    Path<Object> pathIdTagType = fromType.get("idTag");
    Path<Object> pathIdTagRfId = fromRfId.get("id");

    CriteriaQuery<T> select = criteriaQuery.select(fromType);
    select.where(
            criteriaBuilder.equal(pathCode, catName),
            criteriaBuilder.equal(pathIdTagType, pathIdTagRfId));

    TypedQuery<T> q = em.createQuery(select);
    return q.getSingleResult();
}

This makes a "join" ("a filtered cartesian product") between "T" and "RfIdTag".