0

十分之八的事情都连接良好。也就是说，我有时会MongoClient must be connected before calling MongoClient.prototype.db出错。我应该如何更改我的代码以使其可靠地工作（100%）？

我尝试了来自 Now Zeit 平台的创建者之一的代码片段。

我的处理程序

const { send } = require('micro');
const { handleErrors } = require('../../../lib/errors');
const cors = require('../../../lib/cors')();
const qs = require('micro-query');
const mongo = require('../../../lib/mongo');
const { ObjectId } = require('mongodb');

const handler = async (req, res) => {
  let { limit = 5 } = qs(req);

  limit = parseInt(limit);
  limit = limit > 10 ? 10 : limit;

  const db = await mongo();

  const games = await db
    .collection('games_v3')
    .aggregate([
      {
        $match: {
          removed: { $ne: true }
        }
      },
      { $sample: { size: limit } }
    ])
    .toArray();

  send(res, 200, games);
};

module.exports = handleErrors(cors(handler));

我的 mongo 脚本在 lambda 仍然温暖的情况下重用连接：

// Based on: https://spectrum.chat/zeit/now/now-2-0-connect-to-database-on-every-function-invocation~e25b9e64-6271-4e15-822a-ddde047fa43d?m=MTU0NDkxODA3NDExMg==
const MongoClient = require('mongodb').MongoClient;

if (!process.env.MONGODB_URI) {
  throw new Error('Missing env MONGODB_URI');
}

let client = null;

module.exports = function getDb(fn) {
  if (client && !client.isConnected) {
    client = null;
    console.log('[mongo] client discard');
  }

  if (client === null) {
    client = new MongoClient(process.env.MONGODB_URI, {
      useNewUrlParser: true
    });
    console.log('[mongo] client init');
  } else if (client.isConnected) {
    console.log('[mongo] client connected, quick return');
    return client.db(process.env.MONGO_DB_NAME);
  }

  return new Promise((resolve, reject) => {
    client.connect(err => {
      if (err) {
        client = null;
        console.error('[mongo] client err', err);
        return reject(err);
      }

      console.log('[mongo] connected');
      resolve(client.db(process.env.MONGO_DB_NAME));
    });
  });
};

我需要我的处理程序是 100% 可靠的。

4

3 回答 3

1 
  if (client && !client.isConnected) {
    client = null;
    console.log('[mongo] client discard');
  }

此代码可能会导致问题！即使您设置client为null，该客户端仍然存在，将继续连接到 mongo，不会被垃圾收集，并且其回调连接代码仍将运行，但在其回调client中将引用创建的下一个客户端不一定连接。

getDB这种代码的一个常见模式是只从调用中返回一个承诺：

let clientP = null;
function getDb(fn) {
  if (clientP) return clientP;
  clientP = new Promise((resolve, reject) => {
    client = new MongoClient(process.env.MONGODB_URI, {
      useNewUrlParser: true
    });
    client.connect(err => {
      if (err) {
        console.error('[mongo] client err', err);
        return reject(err);
      }

      console.log('[mongo] connected');
      resolve(client.db(process.env.MONGO_DB_NAME));
    });
  });
  return clientP;
};
于 2019-02-22T16:41:20.897 回答
0

我写了这篇文章，讨论无服务器、lambda e db 连接。有一些好的概念可以帮助您找到问题的根本原因。还有一些关于如何缓解连接池问题的示例和用例。

只需查看您的代码，我就可以看出它缺少这个：

context.callbackWaitsForEmptyEventLoop = false;

无服务器：Dynamodb x Mongodb x Aurora 无服务器

于 2019-10-17T01:10:47.993 回答
0

I had the same issue. In my case it was caused by calling getDb() before a previous getDb() call had returned. In this case, I believe that 'client.isConnected' returns true, even though it is still connecting.

This was caused by forgetting to put an 'await' before the getDb() call in one location. I tracked down which by outputting a callstack from getDb using:

console.log(new Error().stack);

I don't see the same issue in the sample code in the question, though it could be triggered by another bit of code that isn't shown.

于 2019-02-22T16:29:55.600 回答