public function getFileCollection($refresh = false)
    {
        if ($refresh || !is_object($this->_fileCollection)) {
            $this->_fileCollection = Yii::createObject([
                'class' => 'yii\mongodb\Collection',
                'database' => $this->database,
                'name' => $this->name
            ]);
        }

        return $this->_fileCollection;
    }