Load object state into a unmapped subclass

luke · **Joined:** Tue May 11, 2004 10:47 am **Posts:** 16

Hibernate 2.1.6

Hi, I have a class A which is persistent (eg, entered in an hbm.xml file). I have a class B which is subclass of A, but is not persistent (not in an hbm.xml file). Can I load the state of an instance of A into an instance of B?

I'm trying to do

Code:

B b = new B();
Serializable aId = // ID of a persistent instance of A.
session.load(b, aId);

but of course I get

net.sf.hibernate.MappingException: No persister for: B

So, I'm looking for something that would work like session.load(Object, Serializable), but would maybe also take the persistent class of the object to load, like

Quote:

session.load(Class cls, Object o, Serializable id)

which would work provided o is a subclass of cls. Does this functionality exist?

Thanks.

anthony · **Posted:** Wed Oct 20, 2004 5:21 pm

take a look at "select new b(a.x,a.y) from a where..."

search projection in the reference guide

morologous · **Joined:** Wed Nov 17, 2004 12:41 pm **Posts:** 2

We have a similar situation.

Based on the above example, how do we persist changes to B?

We get a

Code:

MappingException: No persister for: B

.

How can we achieve persistence for B without mapping B seperately or using a discriminator?

anthony · **Posted:** Tue Nov 23, 2004 12:54 pm

b isn't mapped....

if you want to persist it, just map it...

sounds strange you use select new() to instanciate transcient mapped objet and then want to persist it... but why not, some kind of copy function

morologous · **Joined:** Wed Nov 17, 2004 12:41 pm **Posts:** 2

Thanks. We did decide to map our situation slightly diffierently, and everything worked out.