Find concrete class using a dynamic expression (where a Class instance is passed to a DAO)

Question

I have this method signature:

public int nrOfEntities(Class<? extends MailConfirmation> clazz, User user, String email)

I would like nrOfEntities to return the number of entities that:

• Are of the concrete class clazz
• Have a matching User if user != null
• Have a matching email if user == null

It's the class matching I'm having a problem with. I've tried a few statements without any luck.

Answer 1

If you want to test the class of an object, you should be able to use something like the following:

Object entity = ... // Get the entity however
boolean matchesClass = entity.getClass().equals(clazz);

If this isn't working for you, give some examples of how it fails since it should be this straightforward!

Answer 2

Are you looking for "from " + clazz.getSimpleName() + " where ..."?

Answer 3

Can clazz have subtypes that should not be counted?

If not, is it not sufficient to create the query on clazz?

Criteria criteria = session.createCriteria(clazz);
if (user == null) {
    criteria.add(Restrictions.eq("email", email);
} else {
    criteria.add(Restrictions.eq("user", user);
}
int result = (Integer) criteria.setProjection(Projections.rowCount()).uniqueResult();

Now I am guessing how your mapping looks (that there are "email" and "user" properties).

If that is not working, I know that there is a pseudo property named "class", at least in HQL. Maybe you can experiment with that.