Problem with inheritance and recursive relationship

jonkle · **Joined:** Mon Dec 01, 2003 10:23 am **Posts:** 7

Hi,
I'm new hibernate and have run into a problem where I keep getting WrongClassException for no apparent reason. If someone could help out it would be greatly appreciated. I get the following exception when I try to do the following:

Code:

Item item = (Item)session.load(model.Item.class, new Integer(id));

Here is the exception message:

net.sf.hibernate.WrongClassException: Object with id: 1984 was not of the specified subclass: model.Pack (loaded object was of wrong class)

Here is my mapping:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
   <class name="model.Item" table="Item" discriminator-value="Item">
      <id name="id" type="int" unsaved-value="0">
         <column name="id" not-null="true"/>
         <generator class="identity"/>
      </id>
      <discriminator column="type" type="string" length="10"/>
      <property name="name" type="string" length="100"/>
      <property name="description" type="string" length="1000"/>
      <property name="keywords" type="string" length="50"/>
      <set name="creators" table="ItemCreator" lazy="true">
         <key column="itemId"/>
         <many-to-many column="creatorId" class="model.Creator"/>
      </set>
      <subclass name="model.Volume" discriminator-value="Volume">
         <property name="code" type="string" length="8"/>
         <property name="image" type="string" length="50"/>
         <property name="thumbnail" type="string" length="50"/>
         <many-to-one name="label" column="labelId" class="model.Label"/>
         <set name="packs" table="Item" inverse="true" order-by="name asc" where="type='Pack'" lazy="true">
            <key column="parentItemId"/>
            <one-to-many class="model.Pack"/>
         </set>
      </subclass>
      <subclass name="model.Pack" discriminator-value="Pack">
         <property name="code" type="string" length="8"/>
         <property name="image" type="string" length="50"/>
         <property name="thumbnail" type="string" length="50"/>
         <property name="editor" type="string" length="50"/>
         <property name="visible" type="boolean"/>
         <many-to-one name="volume" column="parentItemId" class="model.Volume"/>
         <set name="files" table="Item" inverse="true" order-by="name asc" where="type='File'" lazy="true">
            <key column="parentItemId"/>
            <one-to-many class="model.File"/>
         </set>
      </subclass>
      <subclass name="model.File" discriminator-value="File">
         <property name="itemFile" type="string" length="50"/>
         <property name="itemFileType" type="string" length="10"/>
         <property name="itemFileSize" type="int" length="10"/>
         <many-to-one name="pack" column="parentItemId" class="model.Pack"/>
      </subclass>
   </class>
</hibernate-mapping>

Worth noting is that the row with id 1984 has type = 'Pack' which is the discriminator that points to model.Pack

Does anyone have a clue?

Thanks in advance,
Jonas Klemming

emmanuel · **Posted:** Mon Dec 01, 2003 11:18 am

The class type loaded model.Pack must be assignable from the parameter class type. This is not the case.

try session.iterate(from Item item where item.id = :id, ...)

jonkle · **Joined:** Mon Dec 01, 2003 10:23 am **Posts:** 7

Thanks for the quick reply!

I tried the session.iterate approach (even though I didn't understand your explaination) and got the same error.

Exception with trace:

Code:

net.sf.hibernate.WrongClassException: Object with id: 1984 was not of the specified subclass: com.primesounds.model.Pack (loaded object was of wrong class) at net.sf.hibernate.loader.Loader.instanceAlreadyLoaded(Loader.java:300) at net.sf.hibernate.loader.Loader.getRow(Loader.java:278) at net.sf.hibernate.loader.Loader.doFind(Loader.java:159) at net.sf.hibernate.loader.Loader.loadEntity(Loader.java:587) at net.sf.hibernate.loader.EntityLoader.load(EntityLoader.java:42) at net.sf.hibernate.persister.EntityPersister.load(EntityPersister.java:396) at net.sf.hibernate.impl.SessionImpl.doLoad(SessionImpl.java:1889) at net.sf.hibernate.impl.SessionImpl.doLoadByClass(SessionImpl.java:1757) at net.sf.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1716) at net.sf.hibernate.type.ManyToOneType.resolveIdentifier(ManyToOneType.java:62) at net.sf.hibernate.type.EntityType.nullSafeGet(EntityType.java:109) at net.sf.hibernate.impl.IteratorImpl.postNext(IteratorImpl.java:57) at net.sf.hibernate.impl.IteratorImpl.<init>(IteratorImpl.java:43) at net.sf.hibernate.hql.QueryTranslator.iterate(QueryTranslator.java:806) at net.sf.hibernate.impl.SessionImpl.iterate(SessionImpl.java:1409) at net.sf.hibernate.impl.SessionImpl.iterate(SessionImpl.java:1386)

What exactly do you mean by:

Quote:

The class type loaded model.Pack must be assignable from the parameter class type. This is not the case.

Regards,
Jonas[/code]

gavin · **Posted:** Mon Dec 01, 2003 11:45 am

I suggest you put a breakpoint in Hibernate code near where the exception occurs. It is much easier to track down these kind of problems this way.

(This is the benefit of open source.)

jonkle · **Joined:** Mon Dec 01, 2003 10:23 am **Posts:** 7

I am unable to debug in my current environment. But from what I can tell it seems it is the many-to-one relationship between model.File and model.Pack that is causing the problem.

Code:

<many-to-one name="pack" column="parentItemId" class="com.primesounds.model.Pack"/>

If I remove this relationship it works.

Unfortunately that relationship is needed elsewhere.

I guess I could recompile the source with some debug-output in the offending function. What information do you need?

Regards,
Jonas

emmanuel · **Posted:** Mon Dec 01, 2003 2:53 pm

I'm not sure this is allowed to share the same column="parentItemId" between different subclasses. You should try to rename it.

is assignable from means that the persistent class must be a superclass or an interface of the class you give to hibernate as load parameter

jonkle · **Joined:** Mon Dec 01, 2003 10:23 am **Posts:** 7

Quote:

I'm not sure this is allowed to share the same column="parentItemId" between different subclasses. You should try to rename it.

That was the problem. Apparently that is not allowed. I renamed parentItemId to packId and volumeId and changed all parentItemId references to their corresponding column and now it works.

It gives me more redundant data in the table but its problaby a cleaner approach.

Thanks for your help! Hibernate Forum is outstanding.

gavin · **Posted:** Tue Dec 02, 2003 10:22 am

No, this is allowed. I just tested this mapping:

Code:

<class name="org.hibernate.test.A" discriminator-value="0" lazy="true">
      <id name="id" column="identifier_column" unsaved-value = "null">
         <generator class="increment"/>
      </id>
      <discriminator column="clazz_discriminata" type="integer" force="true" not-null="false"/>
      <property name="name"/>
      <many-to-one name="forward" class="org.hibernate.test.E" cascade="save-update" />
      <subclass name="org.hibernate.test.B" discriminator-value="null" lazy="true">
         <property name="count" column="count_"/>

         <map name="map">
            <key column="BID"/>
            <index column="MAPKEY" type="string"/>
            <element column="MAPVAL" type="int"/>
         </map>

         <subclass name="org.hibernate.test.C1" discriminator-value="1" lazy="true">
            <property name="address" column="c1"/>
            <one-to-one name="d"/>
            <many-to-one name="c2" column="c" class="org.hibernate.test.C2"/>
            <bag name="c2s" inverse="true" where="clazz_discriminata=2">
               <key column="c"/>
               <one-to-many class="org.hibernate.test.C2"/>
            </bag>
         </subclass>
         <subclass name="org.hibernate.test.C2" discriminator-value="2" lazy="true">
            <property name="address" column="c2"/>
            <many-to-one name="c1" column="c" class="org.hibernate.test.C1"/>
            <bag name="c1s" inverse="true" where="clazz_discriminata=1">
               <key column="c"/>
               <one-to-many class="org.hibernate.test.C1"/>
            </bag>
         </subclass>
      </subclass>
   </class>

And it worked perfectly for the following test:

Code:

   public void testSharedColumn() throws Exception {
      Session s = openSession();
      Transaction t = s.beginTransaction();
      C1 c1 = new C1();
      C2 c2 = new C2();
      c1.setC2(c2);
      c2.setC1(c1);
      s.save(c1); s.save(c2);
      t.commit();
      s.close();

      s = openSession();
      t = s.beginTransaction();
      List list = s.find("from B");
      assertTrue( list.size()==2 );
      t.commit();
      s.close();

      s = openSession();
      t = s.beginTransaction();
      c1 = (C1) s.createQuery("from C1").uniqueResult();
      c2 = (C2) s.createQuery("from C2").uniqueResult();
      assertTrue( c1.getC2()==c2 );
      assertTrue( c2.getC1()==c1 );
      assertTrue( c1.getC2s().contains(c2) );
      assertTrue( c2.getC1s().contains(c1) );
      t.commit();
      s.close();

      s = openSession();
      t = s.beginTransaction();
      c1 = (C1) s.get( A.class, c1.getId() );
      c2 = (C2) s.get( A.class, c2.getId() );
      assertTrue( c1.getC2()==c2 );
      assertTrue( c2.getC1()==c1 );
      assertTrue( c1.getC2s().contains(c2) );
      assertTrue( c2.getC1s().contains(c1) );
      t.commit();
      s.close();

      s = openSession();
      t = s.beginTransaction();
      s.delete(c1); s.delete(c2);
      t.commit();
      s.close();
   }

So thats not the problem!