Java EE (Java Enterprise Edition) General Discussion

hey guys

we're trying to get to the bottom of the following error message but are not able to find a solution, even with help from several search engines and other forums:
Caused by: org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing

We're using spring (and thus also hibernate) and javax.persistence.
We have a bidirectional parent-child relationship between 2 classes, lets call'em Parent and Child.

The following code is inside parent:

public class Parent implements Serializable{
...
private Child childObject;
...
@ManyToOne(cascade = { CascadeType.ALL }, fetch = FetchType.EAGER)
@JoinColumn(name = "child_object")
public Child getChildObject() {
	return childObject;
}
public void setChildObject(Child childObject) {
 	if(childObject != null)
		childObject.register(this);	
	this.childObject = childObject;
}
....
}

The Child-class looks similar to this:

public class Child implements Serializable{
private Set<Parent> parents;
...
@OneToMany(mappedBy="child_object", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
public Set<Parent> getParents() {
	return parents;
}

public void setParents(Set<Parent> parents) {
	this.parents= parents;
}

public void register(Parent parent) {
	this.parents.add(parent);
}
..
}

So far, so good. Now, if we test (using TestNG and extending the test class with AbstractTransactionalTestNGSpringContextTests) this setup using the testcode below, the exception mentioned above is thrown:

public class ChildDAOTest extends AbstractTransactionalTestNGSpringContextTests {
	@Autowired
	private ChildDAO childDAO;
	@Autowired
	private ParentDAO parentDAO;
	@Test
	public void testRegister(){
		Parent parent = TestHelper.createParent("TestParent");
		
		Child child = new Child("ChildTest");
		
		parent.setChildObject(child);
		
		/* save(parent) invokes getJpaTemplate.merge(parent). The implementation JpaParentDAO of interface ParentDAO extends JpaDaoSupport. */
		parent= parentDAO.save(parent);
		
		Parent duplicatedParent = new Parent("duplicate");
		duplicatedParent .setChildObject(parent.getChildObject());
		
		/* the following line throws the exception */
		duplicatedParent = parentDAO.save(duplicatedParent );

}

The problem lies inside setChildObject() of class Parent when executing register() on class Child. Although we know that the exception is caused there, we cannot figure out why and find a proper solution. It seems that there is a problem when adding a transient instance of Parent to a set of Parents inside Child, if Child has already been persisted.

Does anybody have insight on this exception or problem in general? Any help is greatly appreciated!

Cheers, Rox