db.collection 不是函数？什么？

Question

我正在学习 mongodb 并使用以下代码跟随教程：

我的 index.js 文件：

var MongoClient = require('mongodb').MongoClient;

var url = 'mongodb://u****:p****@ds131687.mlab.com:31687/learning_mongo';

var findDocuments = function(db, callback) {
    var collection = db.collection('tours');

    collection.find().toArray(function(err,docs){
        if (err) throw err;
        console.log(docs);
        callback;
    })

}

MongoClient.connect(url, function(err, db){
    if (err) throw err;
    // console.log("it is working");
    // db.close();
    findDocuments(db, function(){
        db.close();
    });
})

不幸的是，我在终端中收到以下错误：

dosstx:~/workspace $ node index.js
/home/ubuntu/workspace/node_modules/mongodb/lib/mongo_client.js:810
        throw err;
        ^

TypeError: db.collection is not a function
    at findDocuments (/home/ubuntu/workspace/index.js:6:25)
    at /home/ubuntu/workspace/index.js:20:5
    at args.push (/home/ubuntu/workspace/node_modules/mongodb/lib/utils.js:404:72)
    at /home/ubuntu/workspace/node_modules/mongodb/lib/mongo_client.js:255:5
    at connectCallback (/home/ubuntu/workspace/node_modules/mongodb/lib/mongo_client.js:933:5)
    at /home/ubuntu/workspace/node_modules/mongodb/lib/mongo_client.js:807:13
    at _combinedTickCallback (internal/process/next_tick.js:73:7)
    at process._tickCallback (internal/process/next_tick.js:104:9)

是否有人对如何继续和/或导致错误的原因有任何建议？ 教程作者没有收到此错误，我看不出还有什么不同之处（其他比可能不同版本的 MongoDB 和作者的版本？）

console.log(db) 显示：

    MongoClient {
  domain: null,
  _events: {},
  _eventsCount: 0,
  _maxListeners: undefined,
  s: 
   { url: 'mongodb://****:****@ds131687.mlab.com:31687/learning_mongo',
     options: 
      { user: *****,
        password: ****,
        socketOptions: {},
        read_preference_tags: null,
        readPreference: [Object],
        dbName: 'learning_mongo',
        servers: [Object],
        auth: [Object],
        server_options: [Object],
        db_options: [Object],
        rs_options: [Object],
        mongos_options: [Object],
        socketTimeoutMS: 360000,
        connectTimeoutMS: 30000,
        promiseLibrary: [Function: Promise] },
     promiseLibrary: [Function: Promise],
     dbCache: {},
     sessions: [] },
  topology: 
   Server {
     domain: null,
     _events: 
      { serverOpening: [Function],
        serverDescriptionChanged: [Function],
        serverHeartbeatStarted: [Function],
        serverHeartbeatSucceeded: [Function],
        serverHeartbeatFailed: [Function],
        serverClosed: [Function],
        topologyOpening: [Function],
        topologyClosed: [Function],
        topologyDescriptionChanged: [Function],
        joined: [Function],
        left: [Function],
        ping: [Function],
        ha: [Function],
        authenticated: [Function],
        error: [Function],
        timeout: [Function],
        close: [Function],
        parseError: [Function],
        open: [Object],
        fullsetup: [Object],
        all: [Object],
        reconnect: [Function] },
     _eventsCount: 22,
     _maxListeners: undefined,
     clientInfo: 
      { driver: [Object],
        os: [Object],
        platform: 'Node.js v6.11.2, LE' },
     s: 
      { coreTopology: [Object],
        sCapabilities: null,
        clonedOptions: [Object],
        reconnect: true,
        emitError: true,
        poolSize: 5,
        storeOptions: [Object],
        store: [Object],
        host: 'ds131687.mlab.com',
        port: 31687,
        options: [Object],
        sessionPool: [Object],
        promiseLibrary: [Function: Promise] } } }

Answer 1

db.collection() 不是最新版本的 MongoDB 中的函数。先卸载最新版本的MongoDB，再安装2.2.33版本的MongoDB。

npm uninstall mongodb  
npm install mongodb@2.2.33

版本 MongoDB >= 3 - 该数据库变量实际上是您尝试访问的对象的父对象。

Answer 2

在新版本的 mongodb 上连接功能发生了变化。这应该工作

var MongoClient = require('mongodb').MongoClient;

var url = 'mongodb://u****:p****@ds131687.mlab.com:31687/learning_mongo';

var findDocuments = function(db, callback) {
    var collection = db.collection('tours');

    collection.find().toArray(function(err,docs){
        if (err) throw err;
        console.log(docs);
        callback;
    })

}

MongoClient.connect(url, function(err, client){
    if (err) throw err;
    // console.log("it is working");
    // db.close();
    findDocuments(client.db('learning_mongo'), function(){
        db.close();
    });
})

更多关于http://mongodb.github.io/node-mongodb-native/3.0/api/的文档

Answer 3

我关注this question 并能够解决错误。基本上，我必须在我的 index.js 文件中添加以下修改：

    MongoClient.connect('mongodb://localhost', function (err, client) {
  if (err) throw err;

  var db = client.db('mytestingdb');

  db.collection('customers').findOne({}, function (findErr, result) {
    if (findErr) throw findErr;
    console.log(result.name);
    client.close();
  });
});