无法使用node.js和Mongodb包查询MongoDB数据库

Question

我无法使用node.js和Mongodb包查询我的MongoDB数据库。

我已经成功地插入，像这样两个对象：

var mongo = require("mongodb"); 
var host = "127.0.0.1"; 
var port = mongo.Connection.DEFAULT_PORT; 
var db = new mongo.Db("nodejs-introduction", new mongo.Server(host, port, { }), {safe: true}); 
console.log(host); 
db.open(function(error) { 
    console.log("We are connected ", + host + ':' + port); 

    db.collection("user", { w:1 }, function(error, collection){ 
     console.log("We have the collection"); 

     collection.insert({ 
      id: "1", 
      name: "Foo Bar", 
      twitter: "Foo_Bar", 
      email: "info@nfoobar.com" 
     }, {w:1}, function() { 
      console.log("Succesfully inserted Foo Bar"); 
     }); 

     collection.insert({ 
      id: "2", 
      name: "Bar Foo", 
      twitter: "Bar_Foo", 
      email: "info@tbarfoo.com" 
     }, {w:1}, function() { 
      console.log("Succesfully inserted Bar Foo"); 
     }); 
    }); 
}); 

一切顺利这里，没有错误。但是如果我想查询像这样的项目：

var mongo = require("mongodb"); 
var host = "127.0.0.1"; 
var port = mongo.Connection.DEFAULT_PORT; 
var db = new mongo.Db("nodejs-introduction", new mongo.Server(host, port, { }), {safe: false}); 
console.log(host); 
db.open(function(error) { 
    console.log("We are connected ", + host + ':' + port); 

    //collection is sort of table 
    db.collection("user", function(error, collection){ 
     console.log("We have the collection"); 
     collection.find({ "id": "1" }, function(error, cursor){ 
      cursor.toArray(function(error, users){ 
       if (users.length == 0) { 
        console.log("no user found"); 
       } else { 
        console.log("Found a user", users[0]); 
       } 
      }); 
     }); 

    }); 
}); 

然后我得到以下错误：

127.0.0.1 
We are connected NaN:27017 
We have the collection 

/path/to/query.js:14 
       if (users.length == 0) { 
         ^
TypeError: Cannot read property 'length' of null 

所以我不解的是，该变量的用户为空并且它不能找到任何比赛，但我不知道为什么。我做错了什么？

Answer 1

找到了解决办法。 Mongodb没有运行。如果Mongodb没有运行，我可以如何插入MongoDB而没有任何错误？