MongoError：使用 NextJs api 时拓扑被破坏

Question

我正在使用 Vercel 无服务器功能为 Next.js 应用程序创建 API 端点。我正在使用 MongoDB 存储对象数组。

我有这个无服务器功能

// api/global/addlink.js

const MongoClient = require("mongodb").MongoClient;
const { ObjectId } = require("mongodb");

const client = new MongoClient(process.env.DB_URI, {});

export default async (req, res) => {
  await client.connect();

  const link = JSON.parse(req.body)["link"];
  const query = { _id: ObjectId(JSON.parse(req.body)["_id"]) };

  const result = await client
    .db("myio_guests")
    .collection("link_groups")
    .findOneAndUpdate(query, {
      $push: {
        links: link,
      },
    });

  res.json({
    message: "link added successfully",
    result: result,
  });

  await client.close();
};

此函数每运行 2 次就会出错。

我尝试了 4 次调用，该函数使用来自我的前端的 fetch post 请求，但只保存了 2 个条目，即第 1 个和第 3 个条目。 如果是第 2 次和第 4 次调用，则会发生此错误：

2021-01-26T14:14:18.964Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    WARN    the options [servers] is not supported
2021-01-26T14:14:18.964Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    WARN    the options [caseTranslate] is not supported
2021-01-26T14:14:18.964Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    WARN    the options [dbName] is not supported
2021-01-26T14:14:18.964Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    WARN    the options [srvHost] is not supported
2021-01-26T14:14:18.964Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    WARN    the options [credentials] is not supported
2021-01-26T14:14:20.203Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    ERROR   MongoError: topology was destroyed
    at executeCommand (/var/task/node_modules/mongodb/lib/operations/db_ops.js:222:21)
    at FindOneAndUpdateOperation.execute (/var/task/node_modules/mongodb/lib/operations/find_and_modify.js:107:5)
    at executeOperation (/var/task/node_modules/mongodb/lib/operations/execute_operation.js:77:17)
    at Collection.findOneAndUpdate (/var/task/node_modules/mongodb/lib/collection.js:1737:10)
    at module.exports.lt9b.__webpack_exports__.default (/var/task/.next/serverless/pages/api/global/addlink.js:296:75)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async apiResolver (/var/task/node_modules/next/dist/next-server/server/api-utils.js:8:1)
    at async /var/task/.next/serverless/pages/api/global/addlink.js:137:387
2021-01-26T14:14:20.203Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    ERROR   MongoError: topology was destroyed
    at executeCommand (/var/task/node_modules/mongodb/lib/operations/db_ops.js:222:21)
    at FindOneAndUpdateOperation.execute (/var/task/node_modules/mongodb/lib/operations/find_and_modify.js:107:5)
    at executeOperation (/var/task/node_modules/mongodb/lib/operations/execute_operation.js:77:17)
    at Collection.findOneAndUpdate (/var/task/node_modules/mongodb/lib/collection.js:1737:10)
    at module.exports.lt9b.__webpack_exports__.default (/var/task/.next/serverless/pages/api/global/addlink.js:296:75)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async apiResolver (/var/task/node_modules/next/dist/next-server/server/api-utils.js:8:1)
    at async /var/task/.next/serverless/pages/api/global/addlink.js:137:387
2021-01-26T14:14:20.204Z    cae61486-ecb3-4726-aa8c-f8e95d9326ad    ERROR   Unhandled Promise Rejection     {"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"MongoError: topology was destroyed","reason":{"errorType":"MongoError","errorMessage":"topology was destroyed","name":"MongoError","stack":["MongoError: topology was destroyed","    at executeCommand (/var/task/node_modules/mongodb/lib/operations/db_ops.js:222:21)","    at FindOneAndUpdateOperation.execute (/var/task/node_modules/mongodb/lib/operations/find_and_modify.js:107:5)","    at executeOperation (/var/task/node_modules/mongodb/lib/operations/execute_operation.js:77:17)","    at Collection.findOneAndUpdate (/var/task/node_modules/mongodb/lib/collection.js:1737:10)","    at module.exports.lt9b.__webpack_exports__.default (/var/task/.next/serverless/pages/api/global/addlink.js:296:75)","    at processTicksAndRejections (internal/process/task_queues.js:97:5)","    at async apiResolver (/var/task/node_modules/next/dist/next-server/server/api-utils.js:8:1)","    at async /var/task/.next/serverless/pages/api/global/addlink.js:137:387"]},"promise":{},"stack":["Runtime.UnhandledPromiseRejection: MongoError: topology was destroyed","    at process.<anonymous> (/var/runtime/index.js:35:15)","    at process.emit (events.js:326:22)","    at processPromiseRejections (internal/process/promises.js:209:33)","    at processTicksAndRejections (internal/process/task_queues.js:98:32)"]}
Unknown application error occurred

如何在这样的无服务器案例中解决此问题？

Answer 1

您遇到的问题来自这一行：

  await client.close();

来自文档：

MongoClient.close() - 关闭底层连接器，进而关闭所有打开的连接。一旦被调用，这个 Mongo 实例就不能再使用了。

意味着当您close 客户端时，任何其他打开的连接也会关闭。 在您的情况下，#2 和 #4 在 #1 和 #3 之后不久（但在它们完成之前）开始运行，并且在它们仍在运行时关闭它们的连接。

也来自文档：

MongoClient 类被设计为线程安全的并且在线程之间共享。通常，您只为给定的数据库集群创建 1 个实例并在您的应用程序中使用它。

最好的做法是为您的无状态函数（我知道）进行一些状态管理，拥有一个连接服务，只为您的无状态函数提供连接，这样管理错误也会更容易。

阅读更多关于此here 和nodejs driver docs

解决您的问题的一个快速（并且非常次优）的方法是在函数中定义连接，如下所示：

// remove the definition from here

export default async (req, res) => {
     // and move it here
     const client = new MongoClient(process.env.DB_URI, {});
     await client.connect();

      .....

     await client.close();
};