yii\mongodb\file\Upload::insertFile PHP Method

    private function insertFile()
    {
        $fileDocument = ['_id' => $this->documentId, 'uploadDate' => new UTCDateTime(round(microtime(true) * 1000))];
        if ($this->filename === null) {
            $fileDocument['filename'] = $this->documentId . '.dat';
        } else {
            $fileDocument['filename'] = $this->filename;
        }
        $fileDocument = array_merge($fileDocument, $this->document, ['chunkSize' => $this->chunkSize, 'length' => $this->length, 'md5' => hash_final($this->hashContext)]);
        $this->collection->insert($fileDocument);
        return $fileDocument;
    }