使用Node.js连接到MongoDB的最佳方法 [英] Best way to connect to MongoDB using Node.js

问题描述

我已经阅读了一些有关如何将Mongo与Node结合使用的指南，它们似乎都以不同的方式连接到数据库.一种对我有效的特定方式是:

I've read a few guides on how to use Mongo with Node, and they all seem to connect to databases differently. One particular way that worked well for me was:

MongoClient.connect("mongodb://localhost:27017/exampleDb", function(err, db) {
  if(err) { return console.dir(err); }

  db.createCollection('users', function(err, collection) {});

  //Do all server/database operations in here

});

但是，对我来说，这似乎效率低下/很奇怪，每次出现app.get()时，我都必须重新连接数据库，例如用于创建新用户或检索信息.

However, this seems inefficient/odd to me, I would have to reconnect to the database every time there is an app.get(), like for making a new user or retrieving information.

似乎更适合我的另一种方法是

Another way that seems better suited to me is

var mongoose = require("mongoose")
var db = mongoose.connect("localhost:27107/users");

db.createCollection('users', function(err, collection) {});

我已经看到几个网站都按照这些原则进行了一些工作，但是我个人无法使上述工作正常进行.我不断收到错误TypeError: db.createCollection is not a function服务器端.因此，我的问题是，如果第一个代码是一个不错的选择，以及是否还有其他方法可以实现上面的代码，为什么不起作用?

I've seen several sites do something along these lines, but I personally can't get the above to work. I keep getting the error TypeError: db.createCollection is not a function server-side. So, my question is why the above code doesn't work, if the first code is a good alternative, and if there are any other ways to do this.

推荐答案

您可以使用全局变量来保持连接(例如db)，例如:

You can use a global variable to hold the connection (e.g. db), for example:

var db = null // global variable to hold the connection

MongoClient.connect('mongodb://localhost:27017/', function(err, client) {
    if(err) { console.error(err) }
    db = client.db('test') // once connected, assign the connection to the global variable
})

app.get('/', function(req, res) {
    db.collection('test').find({}).toArray(function(err, docs) {
        if(err) { console.error(err) }
        res.send(JSON.stringify(docs))
    })
})

或者，如果愿意，还可以使用MongoClient返回的 Promise对象(如果没有回调参数就调用该对象):

Or, if you prefer, you can also use the Promise object that is returned by MongoClient if it is called without a callback argument:

var conn = MongoClient.connect('mongodb://localhost:27017/') // returns a Promise

app.get('/', function(req, res) {
    conn.then(client=> client.db('test').collection('test').find({}).toArray(function(err, docs) {
        if(err) { console.error(err) }
        res.send(JSON.stringify(docs))
    }))
})

请注意，我使用了 ES6粗箭头功能定义在第二个示例中.

Please note that I used the ES6 fat arrow function definition in the second example.

您绝对不应该每次都呼叫MongoClient.使用全局变量或Promises允许MongoDB node.js驱动程序创建连接池，该连接池至少可以实现两个优点:

You are absolutely correct that you should not call MongoClient every time. Using a global variable or Promises allows the MongoDB node.js driver to create a connection pool, which achieves at least two good things:

• 连接在池中被重用，因此在应用程序的生命周期内没有多个昂贵的设置/拆卸过程.您只需连接一次，然后让驾驶员为您照顾其余的一切.
• 您可以通过限制连接池的大小来控制应用程序与数据库的连接量.

编辑2018-08-24 :node.js驱动程序版本3.0及更高版本中的MongoClient.connect()方法返回

Edit 2018-08-24: The MongoClient.connect() method in node.js driver version 3.0 and newer returns a client object instead of a database object. The examples above were modified to keep it up to date with the latest node.js driver version.

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