Subclass w/ discriminator an One-to-many association problem

Saleem Arif · **Posted:** Thu Jul 12, 2007 3:46 pm

Hibernate Version: 3.2

I would like to extend Cat/Domestic Cat inheritance example from

http://www.hibernate.org/hib_docs/v3/reference/en/html_single/

and add a Cage where one or more Domestic Cats can stay together. So I am adding a Cage table with CageID in it and have it in DomesticCat table as foreign key.

While I am trying to load a Cage from Hibernate it is trying to join Cage with both Cat and DomesticCat and failing since cage ID exist only in DomesticCat table.

DomesticCat.hbm.xml contains:

Code:

<many-to-one name="cage" column="CageID" lazy="false" />

Cage.hbm.xml contains:

Code:

<subclass name="DomesticCat" extends="Cat" discriminator-value="DOM">
     <join table="DOMESTIC_CAT">
        <many-to-one name="cage" column="CageID" lazy="false" />
      </join>
</subclass>

Doe any one have idea how to resolve this issue?

Saleem Arif · **Posted:** Thu Jul 12, 2007 3:51 pm

Oops!

Here are correct code segments:

DomesticCat.hbm.xml contains:

Code:

<subclass name="DomesticCat" extends="Cat" discriminator-value="DOM"> 
     <join table="DOMESTIC_CAT"> 
        <many-to-one name="cage" column="CageID" lazy="false" /> 
      </join> 
</subclass> 

Cage.hbm.xml contains:

Code:

<bag name="domesticCats" lazy="false" inverse="true">
    <key column="cageID" not-null="true"/>
    <one-to-many class="DomesticCat"/>
</bag>

TiMiD · **Joined:** Sun Sep 09, 2007 9:26 pm **Posts:** 8

Hello,

I push this topic up since it's unsolved and I'm getting exactly the same problem.

Also, when cascade="all-delete-orphan" is set in the bag definition, and when deleting a Cage, only rows from the "domesticCat" table are deleted, the corresponding rows in the "cat" table are left.

However, when deleting a specific DomesticCat, the corresponding Cat rows are also deleted.

Sounds like a bug ... or another hibernate trick !

sebas · **Joined:** Wed Aug 24, 2005 1:43 pm **Posts:** 10

Hi,
We're experiencing the same problem with Hibernate 3.2.5
any solution identified for this problem?
Thanks,
Sebastien

watsonphill · **Joined:** Fri Feb 08, 2008 6:53 am **Posts:** 4

I'm getting a similar problem when mixing inheritence strategies of subclass and join (as described in the reference document). As I have a large class structure, and I want to avoid lengthy SQL select statements, I have chosen the discriminator strategy. I admit, I've never used it before, so, hopefully, this problem is down to my implementation.

The mapping below is for an entity that sub-classes AbstractOrgEntity using the discriminator method. The OrgUnit has a parent/child relation with entities of the same type, but this is reflected only in the table ORGUNIT and not the table of AbstractOrgEntity.

When I try and retrieve the sub-units of a given OrgUnit, the SQL generated incorrectly references a non-existent PARENT_ID column in the AbstractOrgEntity table.

The problem would seem to be that the <set> for subUnits is not within the <join> element, and so Hibernate assumes the property belongs to the AbstractOrgEntity table. Unfortunately, you can't place the <set> within the <join> as the XML schema disallows it - and I guess Hibernate would complain even if the schema didn't.

I don't think this is a bug as more of an oversight.

Does anyone have a work-around?

Code:

<hibernate-mapping>
  <subclass name="OrgUnit" extends="AbstractOrgEntity" discriminator-value="12">

    <!-- bi-directional one-to-many composite association to OrgUnitType -->
    <!-- this is the parent reference to its children -->
    <set name="subUnits" lazy="true" inverse="true" cascade="all-delete-orphan">
      <key column="PARENT_ID"/>
      <one-to-many class="OrgUnit"/>
    </set>

    <join table="ORGUNIT">
      <key column="id"/>

      <property name="description" column="DESCRIPTION" type="string"/>

      <!-- bi-directional many-to-one composite association to OrgUnitType -->
      <!-- this is the child reference to the parent -->
      <many-to-one name="parent" column="PARENT_ID"
                  class="OrgUnit" not-found="ignore" not-null="false"/>
    </join>
  </subclass>
</hibernate-mapping>