public function back($actions='insert|update|do_delete', $url="")
    {

        if ($url == "") {
            if (count($this->links)) {
                $url = array_pop($this->links);
            } else {
                return $this;
            }
        } else {
            $base = str_replace(Request::path(),'',strtok(Request::fullUrl(),'?'));
            $match_url = str_replace($base, '/', strtok($url,'?'));
            if (Request::path()!= $match_url) {
                $url = Persistence::get($match_url);
            }
        }

        $this->back_on = explode("|", $actions);
        $this->back_url = $url;

        return $this;
    }