Node.js Express /路由和mysql [英] nodejs express/routes and mysql

问题描述

我遇到了一个小问题。我正在尝试制作一个小的API，以检查用户是否已存在于我的数据库中。

I'm facing a little problem. I'm trying to make a small API to check if a user already exists in my DB.

我使用快递和路线，因此可以查询 http://example.com/check/user/john ，它应该输出：true或false，具体取决于用户是否存在于数据库中。

I use express and routes so i can query like "http://example.com/check/user/john" and it should output : true or false depending if the user exists or not in the DB.

在我的路由文件中，我的代码如下：

In my route file i have the code below :

var mysql = require('mysql');
var pool = mysql.createPool({
    host: 'localhost',
    user: 'root',
    password: '123456',
    database: 'nodejs'  
});

module.exports = function(app){
    app.get('/register/check/u/:username', function(req, res){
        var output = 'false';
        pool.getConnection(function(err, conn) {
            query = conn.query('SELECT * FROM users WHERE username LIKE ?', [req.params.username]);
            query.on('error', function(err){
                throw err;
            });
            query.on('result', function(row){
                var output = 'true';
                console.log(row.email);
                console.log(output);
            });
           conn.release();
        });
        res.render('register/check_username', { output: output});
    });
);

问题是 res.render（'register / check_username'，{输出：输出}）; 始终输出： false ，但是在我的控制台日志中它显示 true 用户已经存在。

The problem is that res.render('register/check_username', { output: output}); will always output : false, but in my console log it shows true when the user already exists.

为什么不更新输出变量？

Any idea of why the output variable isn't updated ?

如akaphenom所述，pool.getConnection被初始化为非阻塞进程，因此我的第一个代码自动将输出作为false发送。这是工作代码：

Solution : As explained by akaphenom, the pool.getConnection was beeing initialized into a non-blocking process and therefore my first code was automaticaly sending output as false. Here's the working code :

app.get('/register/check/u/:username', function(req, res){
    pool.getConnection(function(err, conn) {
        var output = 'false';
        query = conn.query('SELECT * FROM users WHERE username LIKE ?', [req.params.username]);
        query.on('error', function(err){
            throw err;
        });
        query.on('result', function(row){
            output = 'true';
        });
        query.on('end', function(result){
            res.render('register/check_username', { output: output});
        });
       conn.release();
    });
});

推荐答案

我相信您不允许非阻塞性这些电话中。将该变量设置为false，将调用连接，然后挂起挂起，等待回调。您可以在回叫完成之前立即呈现响应。

I believe you not allowing for the non-blocking nature of these calls. The variable is set to false the connection is called and then falls through pending a call back. You immediately render the response, prior to the call back completing.

module.exports = function(app){
    app.get('/register/check/u/:username', function(req, res){
        // you set the value of the output var
        var output = 'false';
        // this is a non-blocking call to getConnection which fires the callback you pass into it, once the connection happens.  The code continues on - it doesn't wait.
        pool.getConnection(function(err, conn) {
            query = conn.query('SELECT * FROM users WHERE username LIKE ?', [req.params.username]);
            query.on('error', function(err){
                throw err;
            });
            query.on('result', function(row){
                var output = 'true';
                console.log(row.email);
                console.log(output);
            });
           conn.release();
        });

        // you are getting here before the callback is called
        res.render('register/check_username', { output: output});
    });
);

您为什么在控制台中获得正确的价值？因为最终将调用回调并执行您期望的操作。在res.render后才调用它。

Why do you get the right value in the console? Because eventually the callback is called and performs what you expect. It is just called after the res.render

此代码更可能是您想要的代码：

THis is more likely the code you want:

module.exports = function(app){
    app.get('/register/check/u/:username', function(req, res){
        pool.getConnection(function(err, conn) {
            query = conn.query('SELECT * FROM users WHERE username LIKE ?', [req.params.username]);
            query.on('error', function(err){
                throw err;
            });
            query.on('result', function(row){
                var output = 'true';
                console.log(row.email);
                console.log(output);
                res.render('register/check_username', { output: output});
            });
           conn.release();
        });
    });
);

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