Sub-classing a joined-subclass

ravi · **Posted:** Fri Jul 16, 2004 11:48 am

A <--- B
B extends A as joined-subclass

B<----B1
B<----B2
B<----B3

B1, B2 and B3 are subclasses of B. i'm trying to get the entire B hierarchy into a single table (table per-hierarchy with a discriminator).

since B is already a subclass it has the tag

Code:

<joined-subclass name="B">

now where do i put the discriminator since

Code:

<joined-subclass name="B" discriminator-value="subType">

is not supported

thanks
ravi

Marcos Silva Pereira · **Posted:** Mon Jul 19, 2004 12:07 pm

Hi, i'm get the same problem because the Hibernate DTD does not permit that a joined-subclass have a subclass witch is the way to use a single table per-hierarchy with a discriminator value. Anyone knows how to solve it?

Details:
Hibernate Version: 2.1.4, 02. June 2004
Class headers with XDoclet Tags:

Code:

/**
 * @since 18/07/2004
 * @version 0.1
 * 
 * @hibernate.class discriminator-value="U"
 *                  proxy="br.ufpe.scacin.model.People"
 *                  table="SCACIN_PEOPLE"
 */
public class People implements Identifiable {...}

Code:

/**
 * @since 18/07/2004
 * @version 0.1
 *
 * @hibernate.joined-subclass-key column="USER_ID"
 *
 * @hibernate.joined-subclass proxy="br.ufpe.scacin.model.User"
 *                            table="SCACIN_USER"
 *
 */
public class User extends People {...}

Code:

/**
 * @since 18/07/2004
 * @version 0.1
 *
 * @hibernate.subclass discriminator-value="A"
 *                     proxy="br.ufpe.scacin.model.Administrator"
 */
public class Administrator extends User {...}

In the Administrator class, course, the tags does not work and the class is not mapped.

Thanks by any helps.

michael · **Posted:** Mon Jul 19, 2004 12:44 pm

You can't mix sublcass and joined-subclass

Marcos Silva Pereira · **Posted:** Mon Jul 19, 2004 1:22 pm

michael wrote:

You can't mix sublcass and joined-subclass

Thanks, michael, I know this, I read the DTD. ;-)

But, what is the best approach in this case? I'm thinking in change the relationship between People and User, maybe composition instead inheritance. But this imply make changes on the database and I could not make it. So, what you suggest?

valeuz...

ravi · **Posted:** Mon Jul 19, 2004 1:44 pm

for all the subclasses that i intially wanted to put in a single table, i now went with declaring everything as a joined-subclass. it may be a minor performace issue but that depends only how many subclasses you have.

gavin · **Posted:** Mon Jul 19, 2004 3:35 pm

Hibernate3 solves this by allowing you to mix <subclass> and <join>

jandries · **Posted:** Sat Apr 09, 2005 5:52 am

So B is mapped as a <subclass/> of A with a <join/> in it, resulting in tableA and tableB, with tableB having a foreign key to tableA. If now B1, B2 and B3 are mapped to different tables tableB1, tableB2 and tableB3, everything works fine for me with Hibernate 3.0 final.

If, however, I want to map the fields declared by B1 to the same table tableB that was used for class B, Hibernate will try to insert 2 rows into tableB (one for the B attributes and one for the B1 attributes) when saving an object of class B1.

When selecting the data for an object of class B1 Hibernate is doing a join between tableA, tableB and tableB again, making me think that the Hibernate code does not take into account the fact that the joins in a subclass and a subclass of that subclass can make use of a <join/> to the same table.

Is this a bug, a feature request, or just plain nonsense?

Johan.