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Hibernate version:
3.2.6

Mapping documents:

<hibernate-mapping>
<class entity-name="Persoana" table="PERSOANA">
<id name="id" type="long" column="ID">
<generator class="increment" />
</id>
<property name="pozitie" type="integer" column="POZITIE" />
<property name="representant" type="string" not-null="true" length="48" column="REPRESENTANT" />
<property name="adresa" type="string" length="64" column="ADRESA" />
<property name="identitate" type="string" length="16" column="IDENTITATE" />
<property name="eliberat" type="string" length="24" column="ELIBERAT" />
<property name="informatie" type="string" length="64" column="INFORMATIE" />
</class>
</hibernate-mapping>


<hibernate-mapping>
<typedef class="lang.Cont" name="Cont" />
<class entity-name="Cont" abstract="true" table="CONT">
<id name="id" type="long" column="ID">
<generator class="foreign">
<param name="property">Persoana</param>
</generator>
</id>
<property name="cont" type="Cont">
<column name="CREDIT_CREANTE" />
<column name="CREDIT_RESTANTE" />
<column name="CREDIT_PENALITATI" />
<column name="DEBIT_CREANTE" />
<column name="DEBIT_RESTANTE" />
<column name="DEBIT_PENALITATI" />
</property>
<one-to-one name="Persoana" entity-name="Persoana" constrained="true" />
<union-subclass entity-name="Cont00" table="CONT_00" />
<union-subclass entity-name="Cont01" table="CONT_01" />
<union-subclass entity-name="Cont02" table="CONT_02" />
<union-subclass entity-name="Cont03" table="CONT_03" />
<union-subclass entity-name="Cont04" table="CONT_04" />
<union-subclass entity-name="Cont05" table="CONT_05" />
<union-subclass entity-name="Cont06" table="CONT_06" />
</class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():

sess.beginTransaction();
sess.save("Persoana",map);
for(Leaf l:leaves) {
//Se adauga conturile
// l.getId() goes from 00 to 06
Map tmp=new HashMap();
tmp.put("Persoana",map);
tmp.put("cont", new Cont());
sess.save("Cont"+l.getId(),tmp);
}
sess.getTransaction().commit();

Full stack trace of any exception that occurs:

Caused by: org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [Cont01#1158]
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:168)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
at fiscal.adapt.AdaptC.addPersoana(AdaptC.java:36)
at fiscal.persoana.ModelC.addPersoana(ModelC.java:135)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.reflect.misc.Trampoline.invoke(Unknown Source)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
... 35 more

Name and version of the database you are using:

Postgres 8.2

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

To the second itaration 00,01 the exception is generated.
I think there is no reason to generate it, as the two entities Cont00 and Cont01 represent two differrent classes.