Hello,

I'm a new hibernate user. Every day I understand something new.

My question now is:

I'have implemented a superclass (for example Cat) and a subclass (for example DomesticCat that extends Cat).
Everything runs perfectly, but...
If I would like yo load a Cat but I don't know if it is Cat o DomesticCat, what can I do?

If I load it as Cat, have I something to do to know then if it's a Cat or DomesticCat? Exists something like cat.isInstanceOf(DomesticCat()).

Than you!!

Javier.


Hibernate version: 3

The whole purpose of doing the inheritance structure is that, you need not have to know what class you are retrieving. That is you can query it in polymorphic way. If you want a sub class you can ask for it. cat.isInstanceOf is not a good way of using inheritance.

Agreed. But if you really have to, use Hibernate.getClass().

But it is much, much better OO practice to rely on polymorphism. Use of instanceof is a code smell.

I agree with Gavin's view on "instanceof". If you have to use it many times in your code, probably there is some thing wrong in the way you modeled your class.

Thank you very much all.

Your answers have been very util for me.

Could I obtain a recommendation to the following problem:

DomesticCat has a vaccinationDate attribute, WildCat does not, it doesn't make sense for him to have one. I need to list all the Cats treated by a VetinaryClinic, and print their potential vaccinationDates. Hence I'd iterate though VetinaryClinic.getAllTreatedCats(), check the type, and if it's a DomesticCat, load the appropriate proxy and fetch the vaccinationDate.

Am I incorrect in the assumption that both DomesticCat and WildCat should be mapped to the same table, but only the DomesticCat exposes vacinatedDate attribute? Should I use something along the lines of:

Cat derivedTypeProxy = (Cat) session.load(Hibernate.getClass(cat), cat.getId());
if (derivedTypeProxy instanceof DomesticCat) {
// can fetch the vaccinationDate
}

Is this the recommended way, am I missing something?