无法从mongodb获取文件元数据，因为Gridfs-stream的gfs未定义

Question

我可以通过POST请求使用标准的Gridfs-stream实现将文件上传到mongodb。但是，当我需要通过GET请求查看文件元数据时，我得到了错误：

TypeError: Cannot read property 'files' of undefined

显然，它没有认识到我对gfs.This的定义是我的路由处理器：

router.get('/image/:filename', (req, res) => {

  gfs.files.find({filename: req.params.filename}, function(err, file) {
    let readStream = gfs.createReadStream({filename: file.filename});
    let data = '';
    readStream.on('data', (chunk) => {
      data += chunk.toString('base64');
    })
    readStream.on("error", function (err) {
      res.send("Image not found");
    });
    readStream.pipe(res);
  })

  res.json();
});

我以最简单的方式定义了gridfs-stream：

const conn = mongoose.createConnection(URI, {useNewUrlParser:true, useUnifiedTopology:true});

let gfs;
Grid.mongo = mongoose.mongo;
conn.once('open', () => {
    gfs = Grid(conn.db);
    gfs.collection('uploads');
});

const storage = new GridFsStorage({
    url: URI,
    file: (req, file) => {...}
});

const upload = multer({ storage });

我不明白这里有什么问题，我被困了好几天！

Answer 1

尝试使用以下命令：

​

app.get("/file/:filename", async (req, res) => {
    try {
        const file = await gfs.files.findOne({ filename: req.params.filename });
        const readStream = gfs.createReadStream(file.filename);
        readStream.pipe(res);
    } catch (error) {
        res.send("not found");
    }
});

​