public function callback_before_update($callback = null, $override_all = 0) { if (!$override_all) { $this->callback_before_update_ext[] = $callback; if ($this->callback_before_update == null) { $this->callback_before_update = array($this, 'extended_callback_before_update'); } } else { parent::callback_before_update($callback); } return $this; }