Hi,

Is there anyone out there who could help shed some light on a bug/feature that has been troubling me recently. It appears when there are two classes, A and B, which are connected via a bi-directional one-to-many association and a unidirectional many-to-one from A to B, all with cascade on save-update.

I have put together a simple test case:

Classes:

public class Child {

private java.lang.String _name;
private Parent _parent;
protected java.lang.Long _id;

// standard getters and setters ...

}

public class Parent {

private java.lang.String _name;
private java.util.Set<Child> _children;
private Child _specialChild;
protected java.lang.Long _id;

// standard getters and setters
}

Mappings:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping auto-import="false">
<class
name="Parent"
table="PARENT"
>

<id
name="dbId"
column="DBID"
type="java.lang.Long"
>
<meta attribute="scope-set">protected</meta>
<generator class="native"/>
</id>

<property
name="name"
type="java.lang.String" length="80"
>
<column name="NAME" sql-type="VARCHAR(80)" length="80" />
</property>

<many-to-one
name="SpecialChild"
column="SPECIALCHILDID"
class="Child"
cascade="merge,save-update"
not-null="false"
unique="false"
>
</many-to-one>

<set
name="Children"
table="CHILD"
inverse="true"
cascade="all"
>
<key column="CHILDID"/>
<one-to-many class="Child"/>
</set>

</class>

<class
name="Child"
table="CHILD"
>

<id
name="dbId"
column="DBID"
type="java.lang.Long"
>
<meta attribute="scope-set">protected</meta>
<generator class="native"/>
</id>

<property
name="name"
type="java.lang.String" length="80"
>
<column name="NAME" sql-type="VARCHAR(80)" length="80" />
</property>

<many-to-one
name="Parent"
column="PARENTID"
class="Parent"
cascade="merge,save-update"
not-null="true"
unique="false"
>
</many-to-one>

</class>

</hibernate-mapping>

Test code:

import org.hibernate.Session;
import org.hibernate.FlushMode;
import util.HibernateUtil;

public class Test {

static public void main(String[] args) {

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();

Parent p = new Parent();
p.setName("dad");

Child c1 = new Child();
c1.setName("Bob");
c1.setParent(p);

java.util.Set<Child> cs = new java.util.HashSet<Child>();
cs.add(c1);

p.setChildren(cs);
p.setSpecialChild(c1);

session.save(p);

session.getTransaction().commit();
}
}

Error (I can send the whole stack trace if necessary, but it is huge).

[java] Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: Child.Parent
[java] at org.hibernate.engine.Nullability.checkNullability(Nullability.java:84)

It appears to be a problem with the status of the Parent property at the time that the Child is being saved (it is flagged as SAVING rather than MANAGED) but I simply don't know enough about the guts of hibernate to see what could be causing this. Any help would be much appreciated.

If I remove the cascade on the unidirectional association (specialChild) then it works. If I don't call setSpecialChild in the test script it works too. So presumably it comes down to the way in which circular associations are handled.

you should be marking either of the parents child property, or the childs parent property as inverse="true"

I'd recommend the child property on the parent - the generated SQL will be simpler.

That is how it is currently set up (the Children property on Parent has inverse="true"). The other association is unidirectional so does not have any inverse flag.

Of course, in theory with this arrangements of classes I could set up the unidirectional association as a flag in the child, although there are good reasons why I have to maintain this informaiton in the Parent in this particular case.

add
session.save(c1);
before
session.save(p);
will solve the problem

you have an error in your mapping of Child:
column="PARENTID"
should be
column="CHILDID"