Hello,
I know this is the most basic of functions/issues, but I've spent all night on it and am at a loss. I've read the doc and searched the forums. I'm really stuck.
Below, you'll see I've modeled a bi-directional relationship from Chapter 7 of the Hibernate documentation as best I could. In this example, all I want to do is create a Parent object, assign some Child objects to it as a collection and then persist the entire object graph with session.saveOrUpdate(parent). Whenever I try this, i get the follwing error:
org.hibernate.PropertyValueException: not-null property references a null or transient value: eg.test.Child.parent

I've tried every combination of various attributes, cascades, etc in the mapping file. Below is the mapping and code. Please help, it's killing me.

-------------------------------------------------------


Hibernate 3.0.5
MySQL 4.1



MAP:
<class name="eg.test.Parent">
<id name="id">
<generator class="identity"/>
</id>
<set name="children" inverse="true" cascade="all">
<key column="parent_id"/>
<one-to-many class="eg.test.Child"/>
</set>
</class>

<class name="eg.test.Child">
<id name="id">
<generator class="identity"/>
</id>
<property name="name"/>
<many-to-one name="parent" class="eg.test.Parent" column="parent_id" not-null="true"/>
</class>



CODE:

HashSet set = new HashSet();
Parent p = new Parent();
Child c1 = new Child();
c1.setName("a");
Child c2 = new Child();
c2.setName("b");
set.add(c1);
set.add(c2);
p.setChildren(set);

HibernateUtil.getSession().saveOrUpdate(p);



STACK TRACE:

Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: eg.test.Child.parent
at org.hibernate.engine.Nullability.checkNullability(Nullability.java:72)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:236)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:160)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:95)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:96)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:468)
at org.hibernate.engine.Cascades$5.cascade(Cascades.java:154)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:771)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascadeCollection(Cascades.java:895)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:792)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascade(Cascades.java:847)
at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:363)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:265)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:160)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:95)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:96)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:468)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:463)
at eg.test.TestHibernate2.main(TestHibernate2.java:61)





CLASSES:

public class Parent {
private long id;
private Set children;

public long getId() { return id; }
public void setId(long id) { this.id=id; }

public Set getChildren() { return children; }
public void setChildren(Set children) { this.children=children; }
}

public class Parent {
private long id;
private Set children;

public long getId() { return id; }
public void setId(long id) { this.id=id; }

public Set getChildren() { return children; }
public void setChildren(Set children) { this.children=children; }
}



Thanks!

Somehow, posting a question usually leads me to resolve the problem immediately after posting. A 'delete post' button would be nice :)

Anyway, the issue, is that it looks like in a bidirectional relationship, you must explicitly assign the parent to the child (i.e. both directions).
So what I needed in that example I gave was this...
c1.setParent(p);
c2.setParent(p);

... and that solved the problem. It's shown in one (or more) of the documentation examples, but it somehow escaped me several times.