[SOLVED] How to create an 'instance of' -like query in JPA 2.0?

How to create an 'instance of' -like query in JPA 2.0?

Say we've got an abstract @Entity Animal, and several entity classes that extend Animal, including Dog, Cat, Monkey and Bat.

How can I filter the results based on the extending entity's class?

Example: There are checkboxes where the user can select which entities to retrieve.

[ ] Dog
[X] Cat
[X] Monkey
[ ] Bat

Now I want to retrieve the entities with a (Named)Query defined in the Animal class. What kind of query parameters can I put into the query so that only the Cat and Monkey objects will be returned?

Solution

I'm not absolutely sure it's supported by JPA, but the way to do it in Hibernate, regardless of the inheritance strategy, and thus even if you don't have a discriminator (or didn't map it as a property) is to use the implicit class property :

String jpql = "select a from Animal a where a.class in (:classes)";
Query q = em.createQuery(jpql).setParameter("classes", 
                                            Arrays.asList(Cat.class, Monkey.class));

EDIT :

I just found it's possible in JPA2 using the TYPE operator :

String jpql = "SELECT a FROM Animal a WHERE TYPE(a) IN :classes";
Query q = em.createQuery(jpql).setParameter("classes", 
                                            Arrays.asList(Cat.class, Monkey.class));