/**
  * Relate an object to a child object.
  * @param Model $parent
  * @param Model $child
  * @return static
  */
 public static function relate(Model $parent, Model $child)
 {
     return Relationship::create(['parent_id' => $parent->id, 'child_id' => $child->id, 'parent_object' => $parent->getClass(), 'child_object' => $child->getClass(), 'priority' => Relationship::lastPriority($parent, $child)]);
 }