Hello,

This is probably quite simple but I am not able to quite figure it out. Consider a class Outer which contains an objects of classes Inner1, Inner2, and Inne3. All the Inner classes extend the same class Inner and do not add any attribute to Inner.

I would like to save this by specifying hibernate-mapping for Outer and Inner, but this throws MappingException in net.sf.hibernate.impl.SessionFactoryImpl.getPersister because no ClassPersister can be found for Inner1.

If using the debugger insider this method I set the persister to be the same as that for Inner then the object is saved properly. Also, if I specify the exact same mapping for Inner1 as that for Inner then also the Outer and Inner are saved without error.

So how do I specify that the ClassPersister for Inner1 is same as that for Inner?

For retrieval, I would use a method Outer.setInner1(Inner i) which can construct an Inner1 from the passed parameter.

Thanks in advance.

It cannot be the exact same persister because there is one crucial difference - the classname ;) (which is used as discriminator to be able to distinguish between data that is Inner or actually Inner1)

Thanks, max. But this seems to require a discriminator. Unfortunately I do not know the value of the discriminator column statically; table Inner has a column Type that is foreign key into the the "type" table.

When I did use the persister for the superclass the object was saved correctly. Am I missing something? I do not want Hibernate to determine the correct type of the object during retrieval and instead treat it as an object of the superclass Inner itself.

Thanks in advance for your help. I am hoping I will be able to do this without having to repeat the specification for all the subclasses.

what kind of object model do you have since the class doesn't matter to you when it is retreived ?

Well the class does matter upon retrieval, but I plan to do that by hand:



Does this make sense or am I trying something very stupid?

sorry - can't see how you would do that in a safe manner - how would you ensure integrity for assocations to those objects ? The original object hibernate has recevied won't be updated when you change the "derived" one you create!

Seriously you need the discriminator ... how do *you* decide which Outer that get's to be an inner ?

If you have some magic for that why don't you just do the conversion from Inner to Outer when you need to save ? (note: this is said very ironically because it will be equally bad integrity-wise)

Let me first thank you for the continued promptness of your responses. I know it is easy to loose interest, especially from all accounts I am not doing the "right thing".

I am afraid I might have confused you with the terms. The Outer is always Outer. There are several Inner* types, which all extend Inner. For these Inner* types, only the fieds that are inherited from the superclass Inner need to be persisted.

Actually the conversion that you ironically refer to is the very approach I have been considering: in method getInner1AsInner construct an Inner and return it (to Hibernate) for persisting and during retrieval when Hibernate calls setInner1AsInner construct an Inner1 from the passed parameter and assign it to the field.

the terms on which class comes from where does not matter in this case.

You will have a heck of a time keeping the object graphs in sync.

e.g.

A1->B2 (where B actually is an A)

Save it to hibernate as (A1->A2, but A2 is not B2, it's a new instance - changes to B2 will not be visible on A2 and vice versa)

Loading it from hibernate you get A1->A2, but you "convert" A2 to a B2, but do you remember to make A1 point to B2 also ? and what if there are more references ? ....you are doing something that will mess you up! ;)

If there really is a difference between these objects (there are since you have different classes and i guess methods or implementations for them - then that should be persisted together with them - namely a discriminator.