protected function order()
    {
        foreach ($this->orderBy as $orderBy) {
            if (count($orderBy) == 1) {
                $this->model = $this->model->orderBy($orderBy);
            }

            // field and direction
            if (count($orderBy) == 2) {
                $this->model = $this->model->orderBy($orderBy[0], $orderBy[1]);
            }
        }
    }