private function extractSorting(array $params)
    {
        if (false === $this->issetNotEmpty(self::PARAM_SORTING, $params)) {
            return $this;
        }
        $sort = explode(',', $params[self::PARAM_SORTING]);
        $this->sorting = [];
        foreach ($sort as $field) {
            $direction = 1;
            if (0 === strpos($field, '-')) {
                $direction = -1;
                $field = str_replace('-', '', $field);
            }
            $this->sorting[$field] = $direction;
        }
        return $this;
    }