protected function _getMax()
    {
        $field = $this->_config['right'];
        $rightField = $this->_config['rightField'];
        $edge = $this->_scope($this->_table->find())
            ->select([$field])
            ->orderDesc($rightField)
            ->first();

        if (empty($edge->{$field})) {
            return 0;
        }

        return $edge->{$field};
    }