I'm testing parent - child relationships, and trying to insert two new child
rows in the same transaction. Hibernate raises the following exception message.


" a different object with the same identifier value was already associated with the session: [pctest.Child#0]" . Inserting a single child record works fine.

I've modeled my test using the simple Parent/Child from the documentation example:


<hibernate-mapping>
<class name="pctest.Parent" table="parent" catalog="sampdb1">
<comment></comment>
<id name="id" type="long">
<column name="id" />
<generator class="assigned" />
</id>
<property name="parentName" type="string">
<column name="parent_name" length="40">
<comment></comment>
</column>
</property>
<set name="childs" inverse="true" cascade="all" >
<key>
<column name="parent_id" not-null="true">
<comment></comment>
</column>
</key>
<one-to-many class="pctest.Child" />
</set>
</class>
</hibernate-mapping>



<hibernate-mapping>
<class name="pctest.Child" table="child" catalog="sampdb1">
<comment></comment>
<id name="id" type="long">
<column name="id" />
<generator class="assigned" />
</id>
<many-to-one name="parent" class="pctest.Parent" fetch="select">
<column name="parent_id" not-null="true">
<comment></comment>
</column>
</many-to-one>
<property name="childName" type="string">
<column name="child_name" length="40">
<comment></comment>
</column>
</property>
</class>
</hibernate-mapping>


Here is my Java code:
// The Parent record already exists...

Child child1 = new Child();
child1.setChildName("Sue");
parent.addChild(child1); // parent add child, and child get a reference to it's parent

Child child2 = new Child();
child2.setChildName("Sam");
parent.addChild(child2);

session.flush();


I have tried implementing equals and hashCode on the Child object to use the names;
but that does not solve the problem.

What am I doing wrong? Any help would be greatly appreciated. Thanks.

This is Hibernate 3.2, on MySQL 5


Viewing Parents
Hibernate: select this_.id as id2_0_, this_.state_code as state2_2_0_, this_.parent_name as parent3_2_0_ from sampdb1.parent this_
Parent = Parent1
Hibernate: select children0_.parent_id as parent2_1_, children0_.id as id1_, children0_.id as id1_0_, children0_.parent_id as parent2_1_0_, children0_.child_name as child3_1_0_ from sampdb1.child children0_ where children0_.parent_id=?
Hibernate: select child_.id, child_.parent_id as parent2_1_, child_.child_name as child3_1_ from sampdb1.child child_ where child_.id=?
Exception in thread "main" org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [pctest.Child#0]
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:167)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:186)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:175)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:98)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:507)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:499)
at org.hibernate.engine.CascadingAction$1.cascade(CascadingAction.java:218)
at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:268)
at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:216)
at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:296)
at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:242)
at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:219)
at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
at org.hibernate.engine.Cascade.cascade(Cascade.java:130)
at org.hibernate.event.def.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:131)
at org.hibernate.event.def.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:122)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:65)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at pctest.Main.listParents(Main.java:38)
at pctest.Main.main(Main.java:61)

Thanks for any help.

Your generator class for child's identifier is "assigned", meaning you must manually set the identifier before persisting. Since identifiers must be unique, you will get that exception. Either set the identifiers before flushing or change to a more appropriate id generator.