javascript - MongoClient和Express，连接成功...但是: TypeError: Cannot read property 'collection' of null

Question

我正在尝试使用 MongoClient 而不是 mongoose。但我无法弄清楚为什么无法在我的路由文件中设置新集合。

db/index.js

const {MongoClient} = require('mongodb');

const MONGO_DB_NAME = 'moooongoooo';
const MONGO_PORT = 27017;
const MONGO_URI = `mongodb://localhost:${MONGO_PORT}/${MONGO_DB_NAME}`;
const MONGO_OPTIONS = {
  poolSize: 5,
  useNewUrlParser: true,
  useUnifiedTopology: true
};

class Connection {
  constructor(uri, options, name) {
    this.db = null;
    this.uri = uri;
    this.options = options;
    this.name = name;
  }

  connect() {
    if (this.db) {
      return Promise.resolve(this.db);
    } else {
      return MongoClient.connect(this.uri, this.options).then(client => {
        this.db = client.db(this.name);
        return this.db;
      });

    }
  }
}

module.exports = new Connection(MONGO_URI, MONGO_OPTIONS, MONGO_DB_NAME);

bin/www(摘录)

/**
 * Get MongoDB.
 */

const db = require('../db');

/**
 * Create HTTP server.
 */

var server = http.createServer(app);

/**
 * Connect to MongoDB then listen on provided port, on all network interfaces.
 */

db.connect().then(db => {
  console.log(db);
  server.listen(port);
  server.on('error', onError);
  server.on('listening', onListening);
});

app.js

var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var indexRouter = require('./routes/index');
var usersRouter = require('./routes/users');

var app = express();

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', indexRouter);
app.use('/users', usersRouter);

module.exports = app;

然后我运行服务器。一切都好。

服务器

> nodemon ./bin/www

[nodemon] 1.19.1
[nodemon] to restart at any time, enter `rs`
[nodemon] watching: *.*
[nodemon] starting `node ./bin/www`
Db {
  _events: [Object: null prototype] {},
  _eventsCount: 0,
  _maxListeners: undefined,
  s: {
    dbCache: {},
    children: [],
    topology: NativeTopology {
      _events: [Object: null prototype],
      _eventsCount: 25,
      _maxListeners: undefined,
      s: [Object]
    },
    options: { retryWrites: true, promiseLibrary: [Function: Promise] },
    logger: Logger { className: 'Db' },
    bson: BSON {},
    readPreference: null,
    bufferMaxEntries: -1,
    parentDb: null,
    pkFactory: undefined,
    nativeParser: undefined,
    promiseLibrary: [Function: Promise],
    noListener: false,
    readConcern: undefined,
    writeConcern: undefined,
    namespace: MongoDBNamespace { db: 'moooongoooo', collection: undefined }
  },
  serverConfig: [Getter],
  bufferMaxEntries: [Getter],
  databaseName: [Getter]
}

但是当我尝试将新用户对象发布到数据库时。我收到错误:TypeError:无法读取 null 的属性“集合”

routes/user.js

var express = require('express');
var router = express.Router();

const db = require('../db').db;
const collection = db.collection('users');

router.post('/', (req, res) => {
  collection.insertOne(req.body, (error, result) => {
    if (error) throw error;
    res.send(result);
  })
});

module.exports = router;

Answer 1

您可以更改 app.js，如下所示，等待数据库连接建立，然后需要您的路由。

const express = require('express');
const path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var app = express();

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

let db = require('./db');

this.init = async () => { 
    await db.connect(); // this line waits until db connection established


    //let indexRouter = require('./routes/index');
    let usersRouter = require('./routes/users');
    //app.use('/', indexRouter);
    app.use('/users', usersRouter);
}

this.init()



module.exports = app;