Mongo客户端和快递，连接成功...但是：类型错误：无法读取 null 的属性'collection'

Question

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

数据库/索引.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);
});

应用.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。都很好。

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]
}

但是当我尝试将新的用户对象发布到数据库时，我。 我收到错误：TypeError: Cannot read property 'collection' of null

路由/用户.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

您可以更改应用程序.js如下所示 等到数据库连接建立后，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;