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:

   @ManyToOne
   @JoinColumn(name = "ik_parent_department_id")
   private Department parentDepartment;
   

2. One parent department can have many departments:

   @OneToMany(mappedBy = "parentDepartment")
   private Set<Department> children = new HashSet<Department>(0);
   

And I want to implement the next: When I delete a department, then the ik_parent_department_id parameter of all children of this department is set to null. Any ideas how to do that?

Answer 1

With JPA, in parent Entity you might have something like

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

Answer 2

You'll have to set the children's ik_parent_department_id to null explicitly.

Department parentDepartment = (Department) session.load(Department.class, id);
session.delete(parentDepartment);
for (Department child : parentDepartment.getChildren()){
    child.setParentDepartment(null);
} 
session.flush();

With cascading you would only manage to delete child Departments.