public function getFileCollection($prefix = 'fs', $refresh = false)
    {
        if (is_array($prefix)) {
            list ($dbName, $collectionPrefix) = $prefix;
            if (!isset($collectionPrefix)) {
                $collectionPrefix = 'fs';
            }

            return $this->getDatabase($dbName)->getFileCollection($collectionPrefix, $refresh);
        }
        return $this->getDatabase()->getFileCollection($prefix, $refresh);
    }