了解Node.js处理顺序 [英] Understanding Node.js processing order

问题描述

我在理解Node.js中的处理顺序时遇到问题。
我的问题：
我编写了一个小应用程序，它将会话保存在具有以下属性的cookie中：

I'm having problems understanding the processing order in Node.js. My Problem: I coded a little Application that saves a session in a cookie with the following properties:

session.email = email;
session.randomHash = randomHash;

randomHash var是一个随机String，每次用户登录时都会生成并保存到db。
如果现在有会话的用户想要查看私人页面，则调用方法checkSession（）：

The randomHash var is a random String that gets generated and saved to a db everytime the user logs in. If a user with a session now wants to view a private page the method checkSession() gets called:

exports.checkSession = function(req, res) {
    if(req.session) {
        var User = mongoose.model("User", userSchema);
        User.count({email: req.session.email, randomHash: req.session.randomHash}, function(err, count) {
            if(count === 0) {
                return false;
            }
            if(count === 1) {
                return true;
            }
        });
    }
    else {
        return false;
    }
};

该方法将cookie的randomHash与Db的randomHash值进行比较。
此方法在路径中调用：

The method compares the randomHash of the cookie with the randomHash value of the Db. This method is called in a route:

exports.init = function(req, res) {
    if(hashing.checkSession(req, res)) {
        res.render("controlpanel", {title: "Controlpanel", email: req.session.email});
    }
    else {
        res.send("Sorry but you are not logged in. Go to /login");
    }   
};

现在一定有问题。
由于Nodes非阻塞样式，方法被调用但在if语句执行之前没有完成。
我该怎么办？

Now there must be the problem. Because of Nodes non-blocking style the method gets called but doesn't finish before the if-statement is executed. What can i do about it?

推荐答案

返回 User.count 回调中的值不是的返回值checkSession 。 User.count 回调直到 <$ em> <$ em $ c> c> checkSession 完成后才会运行。

The return value in your User.count callback is not the return value of checkSession. The User.count callback doesn't run until after checkSession has finished.

将回调传递给 checkSession 并在 User.count ：

exports.checkSession = function(req, res, callback) {
    if(req.session) {
        var User = mongoose.model("User", userSchema);
        User.count({email: req.session.email, randomHash: req.session.randomHash}, function(err, count) {
            if(count === 0) {
                callback(false);
            }
            if(count === 1) {
                callback(true);
            }
        });
    }
    else {
        callback(false);
    }
};

并称之为：

exports.init = function(req, res) {
    hashing.checkSession(req, res, function(result) {
        if(result) {
            res.render("controlpanel", {title: "Controlpanel", email: req.session.email});
        }
        else {
            res.send("Sorry but you are not logged in. Go to /login");
        }
    });
};

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