我在使用gridFS将图像文件上传到mongoDB时遇到问题，但是由于某些原因，这不起作用 这是我的代码：

const config = require("config");
const express = require("express");
const router = express.Router();
const dbURI = config.get("mongoURI");
const multer = require("multer");
const crypto = require("crypto");
const path = require("path");
const GridFsStorage = require("multer-gridfs-storage");

var storageImage = new GridFsStorage({
  url: dbURI,file: (req,file) => {
    return new Promise((resolve,reject) => {
      crypto.randomBytes(16,(err,buf) => {
        if (err) {
          return reject(err);
        }
        const filename = buf.toString("hex") + path.extname(file.originalname);
        const fileInfo = {
          filename: filename,bucketName: "user_images"
        };
        resolve(fileInfo);
      });
    });
  }
});
const uploadImage = multer({ storageImage });



router.post("/uploadImage",uploadImage.single("userImg"),(req,res) => {
  console.log("uploading");
  console.log(req.file);
  res.json({ msg: "file uploaded successfully" });
});


module.exports = router;

当我管理.log req.file时，我不确定，有人知道问题出在哪里吗？