On delete set null in hibernate in @OneToMany

Question

I have a Department entity which relations are as follows:

1. Many departments can be in one parent department:

Answer 1

With JPA, in parent Entity you might have something like

@OneToMany(mappedBy="parent", cascade={CascadeType.PERSIST})
Collection children;

and in order to avoid possible repeating "set null code" & integrity violation exceptions on parent removal implement in parent Entity also

@PreRemove
private void preRemove() {
   children.forEach( child -> child.setParent(null));
}