mdm\upload\FileModel::beforeSave PHP Method

    public function beforeSave($insert)
    {
        if ($this->file && $this->file instanceof UploadedFile && parent::beforeSave($insert)) {
            FileHelper::createDirectory(dirname($this->filename));
            if ($this->saveCallback === null) {
                return $this->file->saveAs($this->filename, false);
            } else {
                return call_user_func($this->saveCallback, $this);
            }
        }
        return false;
    }