query = session.query(SubjectCategory)
             query = query.filter_by(intra_extension_id=intra_extension_id, id=subject_category_id)
             ref = query.first()
+            self.del_subject_assignment(intra_extension_id, None, None, None)
             session.delete(ref)
 
     # Getter and Setter for object_category
             query = session.query(ObjectCategory)
             query = query.filter_by(intra_extension_id=intra_extension_id, id=object_category_id)
             ref = query.first()
+            self.del_object_assignment(intra_extension_id, None, None, None)
             session.delete(ref)
 
     # Getter and Setter for action_category
             query = session.query(ActionCategory)
             query = query.filter_by(intra_extension_id=intra_extension_id, id=action_category_id)
             ref = query.first()
+            self.del_action_assignment(intra_extension_id, None, None, None)
             session.delete(ref)
 
     # Perimeter