Question

我正在使用带有节点和mongo后端的React应用程序。 mongo后端将使用Gridfs-stream存储图像。我已经成功实现了图像保存，但是现在无法从数据库中提取特定图像。

gfs.files.findOne的功能正常运行，直到将其移至单独的文件并将其添加到模块导出中为止。我不知道是什么原因导致执行失败。

在database.js中获取图像：

exports.getFile = (filename) => {
  console.log('loading file: ' + filename);
  gfs.files.findOne({ filename : filename }, (err, file) => {
    console.log('finding file');
    if (file) {
      // checking specifically for image here
      if (file.contentType == 'image/png' || file.contentType == 'image/jpeg') {
        res.set('Content-Type', file.mimetype);
        const readstream = gfs.createReadStream(file.filename);
        console.log('returning readstream');
        return readstream; 
      }
      else {
        console.log('error loading');
        const err = { "status": "error", "details": "File is not an image" };
        return err;
      }
    }
    else {
      console.log('error loading');
      const err = { "status": "error", "details": "Failed to find specified file" };
      return err;
    }
  });
  console.log('function ending');
}

在api中调用函数路由users.js：

let rs = database.getFile(pic.profilePicture);
if (rs.status && rs.status === "error") {
    res.json(rs);
}
else {
    // we have a readstream
    rs.pipe(res);
}

控制台输出在终端：

[0] testing retrieving profile picture
[0] loading file: 7be7c6a99a96023763b753febd85a92e.png
[0] function ending
[0] events.js:173
[0]       throw er; // Unhandled 'error' event
[0]       ^
[0] 
[0] TypeError: Cannot read property 'status' of undefined
[0]     at User.getProfilePicture (/Users/zachdobbs/Documents/Projects/Better/routes/api/users.js:44:20)
[0]     at /Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/model.js:4698:16
[0]     at /Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/query.js:4099:12
[0]     at process.nextTick (/Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/query.js:2681:28)
[0]     at processTicksAndRejections (internal/process/next_tick.js:74:9)
[0] Emitted 'error' event at:
[0]     at /Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/model.js:4700:13
[0]     at /Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/query.js:4099:12
[0]     at process.nextTick (/Users/zachdobbs/Documents/Projects/Better/node_modules/mongoose/lib/query.js:2681:28)
[0]     at processTicksAndRejections (internal/process/next_tick.js:74:9)
[0] [nodemon] app crashed - waiting for file changes before starting...

据我所见，gfs.files.findOne函数正在跳过整个块，并直接转到函数的末尾。显示的唯一日志是loading file: ...png和function ending输出。这些日志位于函数的开头和结尾，但是函数内的其他日志均未执行。我不知道为什么会这样。如果有人可以帮助我解决这个问题，将不胜感激。

Answer 1

赞：

exports.getFile = (filename) => {
  console.log('loading file: ' + filename);
  gfs.findOne({ filename : filename }, (err, file) => {
    console.log('finding file');
    if (file) {
      // checking specifically for image here
      if (file.contentType == 'image/png' || file.contentType == 'image/jpeg') {
        res.set('Content-Type', file.mimetype);
        const readstream = gfs.createReadStream(file.filename);
        console.log('returning readstream');
        return readstream; 
      }
      else {
        console.log('error loading');
        const error = { status: "error", details: "File is not an image" };
        return error;
      }
    }
    else {
      console.log('error loading');
      const error = { status: "error", details: "Failed to find specified file" + err };
      return error;
    }
  });
  console.log('function ending');
}

然后：

let rs = database.getFile(pic.profilePicture);
if (rs.status && rs.status === "error") {
    res.json(JSON.stringify(rs));
}
else {
    // we have a readstream
    rs.pipe(res);
}

为什么导出的Gridfs函数不能正确执行？

1 个答案: