ManyToOne - Problems managing relationships
Dear All,
I have a simple Parent-Child relationship as illustrated by the following entities:
@Entity(access = AccessType.FIELD)
class ParentBean implements Serializable
{
@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL)
private Collection<ChildBean> children;
Collection<ChildBean> getChildren()
{
return children;
}
void removeChild(ChildBean child)
{
children.remove(child);
}
addChild(ChildBean child)
{
children.add(child);
child.setParent(this);
}
}@Entity(access = AccessType.FIELD)
class ChildBean implements Serializable
{
@ManyToOne
private ParentBean parent = null;
void setParent(ParentBean parent)
{
// if this child is already associated with a parent, remove
// the old association.
if (this.parent!=null)
{
this.parent.removeChild(this);
}
this.parent = parent;
}
}i.e. The Child entity owns the relationship. The relationship is formed by calling the addChild method on the Parent. If we attempt to add a Child to a Parent with Child that has already been added to a Parent, in order to avoid vilating the one-ness of this relationship, we call removeChild on teh previous Parent after adding to the new one.
Or at least that is what I want to happen. However if I do the following:
//construct a parent object and add a child to it ParentBean parentOne = new ParentBean(); ChildBean childOne = new ChildBean(); parentOne.addChild(childOne); manager.merge(parentOne); //construct a new parent and add the same child ParentBean parentTwo = new ParentBean(); parentTwo.addChild(childOne); manager.merge(parentTwo);
I find that both parentOne and parentTwo are associated with different Child entities, looking in the database it would appear that the Child has been cloned and each Parent has a copy.
Furthermore, if I change the EntityManager operations from merge to persist, I get a TransientObjectException thrown.
Can anyone tell me what I am doing wrong. As I said, all I want is that if I add a Child to a parent, that any previous Parent associations of that Child are removed.
BTW. I am using JBoss 4.0.3 SP1
Regards,
Colin E.
