Mapping class & subclass to same table without discrimin

TheXFed · **Posted:** Thu Mar 23, 2006 12:38 pm

(First, I'd like to Note that the only reason for this is to support legacy schema/code in our app)

I have class A, which is a hibernate entity with generated primary keys. However, there is one case where the primary key actually needs to be assigned. For this, I create class B (which extends A), and override the primary key getter/setter, and map it as an "assigned" pk.

Basically, the mapping document for B is identical to A, except for this primary key generator.

So far this is OK. The reason this works, is because I never have to retrieve a B. I only need to save a B, and later it will always be viewed as an A.

The Problem:
I have a one-to-many collection mapped as a bag, with the collection key set as not-null="true". This is necessary, since this ensures that the FK will always be set on an Insert.

Since both A and B have this mapping, and B is actually an A, somewhere under the hood 2 identical "Backrefs" are created, causing an exception on hibernate initialization:

Code:

org.hibernate.MappingException: duplicate property mapping: _customFieldsBackref at org.hibernate.mapping.PersistentClass.checkPropertyDuplication(PersistentClass.java:389) at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:379) at org.hibernate.mapping.RootClass.validate(RootClass.java:192) at org.hibernate.cfg.Configuration.validate(Configuration.java:983) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1147) at

I traced through the hibernate source, and found that using not-null="true" for the collection key, creates these "Backref" pointers. Since I have B extending A, it thinks B is actually an A, and creates 2 identical Backref pointers.

Any suggestions for a different way to handle this?

Hibernate version: 3.1

Mapping documents:
Both A.hbm.xml and B.hbm.xml have this mapping for the one-to-many collection:

Code:

        <bag
            name="customFields"
            lazy="true"
            inverse="false"
            cascade="all-delete-orphan"
        >
            <key
                column="itemId"
                not-null="true"
            >
            </key>

            <one-to-many
class="test.CustomField"
            />
      </bag>

TheXFed · **Posted:** Thu Mar 23, 2006 2:39 pm

I modified my mapping and it fixed the problem.

From:

Code:

<bag
            name="customFields"
            lazy="true"
            inverse="false"
            cascade="all-delete-orphan"
        >
            <key
                column="itemId"
                not-null="true"
            >
            </key>

            <one-to-many
                class="test.CustomField"
            />
      </bag> 

To:

Code:

<bag
            name="customFields"
            lazy="true"
            inverse="false"
            cascade="all-delete-orphan"
        >
            <key>
               <column
                  name="itemId"
                  not-null="true"
               >
               </column>
            </key>

            <one-to-many
                class="test.CustomField"
            />
      </bag> 

The difference being the use of the column element as opposed to the column & not-null attributes in <key>.

TheXFed · **Posted:** Fri Mar 24, 2006 10:47 am

Ok I may have gotten too excited when I saw the different mapping which looked like it would work the same. What i found, is that using the <column name="..." not-null="true"/> element DOES NOT seem to work correctly. It seems to ignore the not-null, since it tries inserting WITHOUT the foreign key.