public function buildSortFields($fields)
    {
        $sortFields = [];
        foreach ((array)$fields as $key => $value) {
            if (is_int($key)) {
                $sortFields[$value] = +1;
            } else {
                if ($value === SORT_ASC) {
                    $value = +1;
                } elseif ($value === SORT_DESC) {
                    $value = -1;
                }
                $sortFields[$key] = $value;
            }
        }
        return $sortFields;
    }