如何从node.js中的mysql SELECT查询返回一个值

Question

我仍然是Node.js的新手,我正在努力了解回调是如何工作的.所以,这是我的问题:

我应该放更多代码:

POST:

app.post('/register', function(req, res) {

    //get data from the request
    var data = {
        username: req.body.username,
        email: req.body.email,
        password: req.body.password
    };

    function fetchID(callback) {
        connection.query('SELECT id_user FROM USERS WHERE username = ?', data.username, function(err, rows) {
            if (err) {
                callback(err, null);
            } else 
                callback(null, rows[0].id_user);
        });
    }
    var user_id;
    fetchID(function(err, content) {
        if (err) {
            console.log(err);
            return next("Mysql error, check your query");
        } else {
            user_id = content;
            console.log(user_id); //undefined
        }
    });

    console.log(user_id); //undefined
    var payload = {
        iss: req.hostname,
        sub: user_id
    }
    console.log(payload.sub); //correct id
})

GET:

app.get('/todos', function(req, res) {
    if (!req.headers.authorization) {
        return res.status(401).send({
            message: 'You are not authorized !'
        });
    }

    var token = req.headers.authorization.split(' ')[1];
    var payload = jwt.decode(token, "shhh..");

    //additional level of security
    console.log('sub id is : ' + payload.sub); //undefined
    if (!payload.sub) {
        return res.status(401).send({
            message: 'Authentication failed !'
        });
    }

})

我评论每个console.log更清楚.当我if (!payload.sub)在app.get()中检查时,我需要获取正确的ID

Answer 1

你的两个功能应该是这样的 -

function fetchID(data, callback) {
        connection.query('SELECT id_user FROM USERS WHERE username = ?', data.username, function(err, rows) {
            if (err) {
                callback(err, null);
            } else 
                callback(null, rows[0].id_user);
        });
}

然后

var user_id;

fetchID(data, function(err, content) {
    if (err) {
        console.log(err);
        // Do something with your error...
    } else {
        user_id = content;
    }
});

在回调函数中,返回的变量content将保存值user_id.

编辑

我没有解决你上面描述的确切问题.

但是在下面的例子中,我已经表明,回调机制正在运行 -

首先(创建表并插入一些虚拟数据) -

use test;
create table users (id int(11) primary key,username varchar(100));
insert into users values(1, "John");
insert into users values(2, "Sham");

现在我已经将你的post方法设置为get并在浏览器中进行测试.

以下是在我的localhost中测试的完整课程 -

var application_root = __dirname,
    express = require("express"),
    mysql = require('mysql');
var app = express();
var connection = mysql.createConnection({
  host : 'localhost',
  user : 'root',
  password : 'admin',
  database: "test"
});
app.get('/getuser', function(req, res) {
  //get data from the request
    var data = {
        username: req.query.username
    };
    function fetchID(data, callback) {
        connection.query('SELECT id FROM users WHERE username = ?',        
               data.username, function(err, rows) {
            if (err) {
                callback(err, null);
            } else 
                callback(null, rows[0].id);
        });
    }
    var user_id;
    fetchID(data, function(err, content) {
        if (err) {
        console.log(err);
        res.send(err);  
        // Do something with your error...
        } else {
        user_id = content;
        console.log(user_id);
        res.send("user id is -" + user_id);
        }
    });
})
app.listen(1212);

现在这些请求将产生此输出 - http://127.0.0.1:1212/getuser?username=john=> user id is -1和 http://127.0.0.1:1212/getuser?username=sham=>user id is -2

希望这段代码示例能帮助您理解node.js中的回调.

谢谢