How can i add an extra column value when adding files

Aryan1703

 ->join(
        Mjoin::inst('ops_analysisImg')
            ->link('ops_dailyLog.id', 'ops_imglinktable.logID')
            ->link('ops_analysisImg.id', 'ops_imglinktable.imgID')
            ->fields(
                Field::inst('id')
                    ->upload(
                        Upload::inst($_SERVER['DOCUMENT_ROOT'] . '/operations/uploads/__NAME__')
                            ->db(
                                'ops_analysisImg',
                                'id',
                                array(
                                    'filename' => Upload::DB_FILE_NAME,
                                    'filesize' => Upload::DB_FILE_SIZE,
                                    'web_path' => Upload::DB_WEB_PATH,
                                )
                            )
                            ->validator(Validate::fileSize(750000, 'Files must be smaller that 750K'))
                            ->validator(Validate::fileExtensions(array('png', 'jpg', 'jpeg', 'gif'), "Please upload an image"))
                    )
            )
    )

i have a column in database "upload_date(datetime) where i want to store current timestamp