public function add($for, $for_id, $user_id, $action, $data = '')
	{
		$history = new $this->model;
		$history->for = $for;
		$history->for_id = $for_id;
		$history->user_id = $user_id;
		$history->action = $action;
		$history->data = is_array($data) ? json_encode($data) : $data;

		$history->save();

		return $history;
	}