Persist subclass instance with superclass mapping

jayaramanettar · **Joined:** Mon Dec 04, 2006 1:50 am **Posts:** 2

Hi,

I am facing a problem related to Hibernate Mapping.

I have the following data beans:

Code:

public class A
{
    int id;
    String name;
}

public class B extends A
{
    String address;
}

I have mapped class A with table A.

Now, I have something like:

Code:

A obj = new B();

I want to persist obj in table A (only id and name) without defining a mapping for class B. I want the extra data in obj (address) to be discarded.

If I write session.save(obj), it gives me an error saying that there is no mapping for class B.

Is it possible to persist obj without defining a mapping for B?

Regards,
Jayarama Nettar.

steckemetz · **Posted:** Mon Dec 04, 2006 6:26 am

I dont think that this is possible with hibernate.
The reason may be something like:

hibernate does not throw information away when persisting instances.
In your case, obj is instance of B and this information
would be discarded.

lkline · **Joined:** Wed Sep 21, 2005 11:52 am **Posts:** 43

I don't know if this would work, but here is my idea.

Define an interface, call it I, that A implements. Define the hibernate mapping for the interface only. Define only those properties that you want saved.

The problem I see is how would Hibernate know which concrete class to instantiate when it loads an object from the table?

It's not really that difficult to create mappings that have inheritance relationships. That way you can still store A and B in the same table and retrieve them as instances of the correct class. As long as you define no extra properties for B it will be saved with only the properties it inherits from A.

Good luck. Don't forget to rate.