将NodeJS与MongoDB驱动程序一起使用时，Cursor和Collection始终为null？

Question

我有以下代码片段，它永远不会返回“user”集合中的数据。光标（项目）始终为空/空。

var fs  = require("fs");
var express = require("express");
var mongo = require("mongodb");
var config = JSON.parse( fs.readFileSync("config.json") );
var host = config.host;
var port = config.port;

var mongoHost = config.mongohost;
var mongoPort = mongo.Connection.DEFAULT_PORT;


var app = express();
var db = new mongo.Db("heelodb", new mongo.Server(host, port, {}));

app.use(app.router);
app.use(express.static(__dirname + "/public"));


app.get("/", function(request, response){
    response.send("hello");
});

app.post("/api/checkEmail", express.bodyParser(), function(request, response) {
    var email = request.body.email;
    db.open(function(error){
        console.log("We are connected to mongo! " + mongoHost + ":" + mongoPort);

        var collection = db.collection("user");
        collection.find().toArray(function(error, items){
            console.log("collection name: " + collection.collectionName);
            console.log("items: " + items);

        });



    });

});

app.listen(port, host);

当我直接查询mongodb数据库时，我总是得到结果。见下文。

> db.user.find();
{ "_id" : ObjectId("52d6ef186a7a9c49af4d61c2"), "email" : "zaheer@heelo.co" }
{ "_id" : ObjectId("52d6ef1b6a7a9c49af4d61c3"), "email" : "zaheerbaloch@live.com" }

请帮忙！