使用Node.js在MongoDB操作中回调(Callback at MongoDB Operation With Node.js)

 出于组织目的，我将源代码分离为模块，例如我在node.js应用程序上有user模块，该应用程序负责从MongoDB数据库中检索用户信息。 我正在做这样的事情： 
 
var mongo = require("mongodb"),
    Server = mongo.Server,
    Db = mongo.Db;

var server = new Server("localhost", 27017, { auto_reconnect: true });
var db = new Db("users", server);

module.exports = {
    login: function(user, pass, callback) {
        var reg_result = null;

        db.open(function (err, db) {
            if(!err) {
                db.collection("users", function(err, collection) {
                    collection.findOne(
                        {
                            "username": user,
                            "password": pass
                        },
                        function(err, item) {
                            if(!err) {
                                reg_result = item;
                            } else {
                                reg_result = "error";
                            }
                        }
                    );
                });
            } else {
                reg_result = "error";
                console.log("ERROR: " + err);
            }
        });

        callback(reg_result);
    }
}
 
 并在我的测试脚本上执行它，如下所示： 
 
var user = require("./user.js");

user.log("test", "test", function(msg) {
    console.log(msg);
});
 
 它执行数据库操作并检索值，但每次只返回null ，当我不初始化reg_result变量时，它返回undefined 。 我该怎么做才能纠正这个问题？ 
 
 我在user.js上使用console.log调试并输出了user.js ，但是我想要回调，所以我可以在其他源上使用该项，比如我的测试脚本 

For organization purposes I'm separating my source code into modules, for example I have the user module on my node.js app which is responsable for retrieving user information from a MongoDB database. I'm doing something like this:
 
var mongo = require("mongodb"),
    Server = mongo.Server,
    Db = mongo.Db;

var server = new Server("localhost", 27017, { auto_reconnect: true });
var db = new Db("users", server);

module.exports = {
    login: function(user, pass, callback) {
        var reg_result = null;

        db.open(function (err, db) {
            if(!err) {
                db.collection("users", function(err, collection) {
                    collection.findOne(
                        {
                            "username": user,
                            "password": pass
                        },
                        function(err, item) {
                            if(!err) {
                                reg_result = item;
                            } else {
                                reg_result = "error";
                            }
                        }
                    );
                });
            } else {
                reg_result = "error";
                console.log("ERROR: " + err);
            }
        });

        callback(reg_result);
    }
}
 
And executing it on my test script like this:
 
var user = require("./user.js");

user.log("test", "test", function(msg) {
    console.log(msg);
});
 
It does the database operation and retrieves the value, but every time it only returns null, when I don't initialize the reg_result variable it returns undefined. What should I do to correct this?
 
I debugged using console.log on the user.js and the item was outputted, but I want to have the callback so I can use the item on other sources, like my test script

原文：https://stackoverflow.com/questions/9743564