protected static function restGetSortField($default = false)
    {
        $sort = Request::getInstance()->query('_sort', false);
        if (!$sort) {
            return $default;
        }

        $sortDirection = substr($sort, 0, 1);
        if ($sortDirection == '+' || $sortDirection == '-') {
            return substr($sort, 1);
        }

        return $sort;
    }