JPA OneToMany bidirectional -- Entity deletion

Question

I am having trouble deleting an entity part of a part-whole hierarchy and mapped as a OneToMany bidirectional relationship. For example:
public class A {
    @OneToMany(mappedBy="parent", cascade={CascadeType.MERGE, CascadeType.PERSIST})
    private Collection<A> children;
    @ManyToOne(cascade={CascadeType.MERGE, CascadeType.PERSIST})
    @JoinColumn(name="PARENT_ID")
    private A parent;
}Instances of 'A' can, but do not HAVE to participate in this relationship. Therefore, a cascade on remove is not appropriate, because for any given instance of 'A', a parent and/or any of the children can exist independent of that instance.
So basically I want to remove an instance of 'A', and at the same time have it's child relationships updated -- basically pointing to a null parent.
What's the proper way to do this?
The first and most obvious way to me is:
    entityManager.remove(instanceOfA);But that results in the cryptic error: "deleted entity passed to persist".
The only way I've gotten this to work so far is to use two transactions. In the first, I simply break the relationships and merge the objects:
    Collection<A> children = instanceOfA.getChildren();
    instanceOfA.setChildren(null);
    for(A child : children) {
        child.setParent(null);
        entityManager.merge(child);
    entityManager.merge(instanceOfA);And in the second transaction:
    instanceOfA = entityManager.find(A.class, instanceOfA.getId());
    entityManager.remove(instanceOfA);This works, but feels very clunky.
What is the proper way to do this?
Thanks,
Justin

Answer 1

I am having trouble deleting an entity part of a part-whole hierarchy and mapped as a OneToMany bidirectional relationship. For example:
public class A {
    @OneToMany(mappedBy="parent", cascade={CascadeType.MERGE, CascadeType.PERSIST})
    private Collection<A> children;
    @ManyToOne(cascade={CascadeType.MERGE, CascadeType.PERSIST})
    @JoinColumn(name="PARENT_ID")
    private A parent;
}Instances of 'A' can, but do not HAVE to participate in this relationship. Therefore, a cascade on remove is not appropriate, because for any given instance of 'A', a parent and/or any of the children can exist independent of that instance.
So basically I want to remove an instance of 'A', and at the same time have it's child relationships updated -- basically pointing to a null parent.
What's the proper way to do this?
The first and most obvious way to me is:
    entityManager.remove(instanceOfA);But that results in the cryptic error: "deleted entity passed to persist".
The only way I've gotten this to work so far is to use two transactions. In the first, I simply break the relationships and merge the objects:
    Collection<A> children = instanceOfA.getChildren();
    instanceOfA.setChildren(null);
    for(A child : children) {
        child.setParent(null);
        entityManager.merge(child);
    entityManager.merge(instanceOfA);And in the second transaction:
    instanceOfA = entityManager.find(A.class, instanceOfA.getId());
    entityManager.remove(instanceOfA);This works, but feels very clunky.
What is the proper way to do this?
Thanks,
Justin