multer multiple upload, req.files.filename undefined

helpp, i get error, undefined when i console.log(req.files.filename)

const storage = multer.diskStorage({
  destination : path.join(__dirname + './../../public/images/event/'),
  filename: function(req, file, cb){
    cb(null, file.fieldname + '-' + Date.now() +
    path.extname(file.originalname));
  }
});

//init upload
const upload = multer({
  storage : storage
}).array('event_thumbnail');


upload(req, res, err => {
    const all_size = req.files.length
    const data = req.body
    const MY_NAMESPACE = '1b671a64-40d5-491e-99b0-da01ff1f3341'
    const batchs = datetime.create().format('Y-m-d H:M')+data.username
    const uuid = uuidv5(batchs, MY_NAMESPACE)
   for(i =0 ; i < all_size; i++){
      console.log(req.files) 
    //result
    { fieldname: 'event_thumbnail',
    originalname: 'Raisa1.jpg',
    encoding: '7bit',
    mimetype: 'image/jpeg',
    destination: '/media/kevin/e076659f-74c7-40d8-beb3-767a81db9a63/Orlenda/admin_orlenda/public/images/event/',
    filename: 'event_thumbnail-1523950949132.jpg',
    path: '/media/kevin/e076659f-74c7-40d8-beb3-767a81db9a63/Orlenda/admin_orlenda/public/images/event/event_thumbnail-1523950949132.jpg',
    size: 57924 }   

      pool.query(
        `INSERT INTO event_thumbnails(event_thumbnail, 
              uuid, updated_at, created_at)
          VALUES('${req.files.filename}', '${uuid}',
              '${datetime.create().format('Y-m-d H:M:S')}',
              '${datetime.create().format('Y-m-d H:M:S')}')`
      ,function(err, result){ 
    console.log(req.files.filename); //result undefined
    res.end() })
    }
            

})