为什么我无法在Node.js中保存和检查会话？

Question

我正在学习nodejs，我想通过检查session.login值来检查用户是否登录，但是在创建session.login然后将用户重定向到主页时，session.login仍然是未定义的。 发出“已记录”只是将用户重定向到仪表板，但是仪表板会检查session.login是否存在，它显示未定义，并且用户会再次重定向到登录页面。

var app = require('express')(); //load and initialize express
var http = require('http').Server(app); //create http server
var io = require('socket.io')(http); //add socket to http server
var path = require('path') //initialize path module
var port = 3000; //define port
var mysql = require('mysql'); //load mysql module
var session = require('express-session'); //sessions module
var login; //login
var md5 = require('md5');

//connecting to the database
var con = mysql.createConnection({
    host : 'localhost',
    user : 'root',
    password : '',
    database : 'chat'
});

con.connect((error) => {
    if(error) console.log('Error with database connection.');
    else console.log("Connected to the database!");
});

//define default path
app.use(require('express').static(path.join(__dirname, 'public'))); 

//session
app.use(session({
    secret: 'randomstringhere',
    resave: false,
    saveUninitialized: false,
    cookie: {

    }
}));

app.get('/', (req, res) => {
    if (req.session.login) {
        res.redirect('/dashboard');
    }
    else {
        res.sendFile(__dirname + '/views/login.html');
        console.log("Someone has joined to the server.");

        io.on('connection', (socket) => {
            //login
            socket.on('login', (login, password) => {
                con.query('SELECT * FROM users WHERE login="'+login+'" AND password="'+md5(password)+'"', (error, results, fields) => {
                    if (error) console.log('Error');
                    if (results[0]) {
                        req.session.login = results[0].login;
                        console.log(req.session.login+": Succesfully logged.");
                        req.session.save();
                        socket.emit('logged', 'You will be logged, please wait!');//redirects to /dashboard
                    }
                    else {
                        socket.emit('cant login', 'Login or password incorrect!');
                        console.log("Incorrect login or password.");
                    }
                });
            });
        });
    }
});

app.get('/dashboard', (req, res) => {
    if (req.session.login) {
        res.sendFile(__dirname + '/views/index.html');
        console.log(req.session.login + " has joined to the server.");

        io.on('connection', (socket) => {
            socket.on('message', (msg) => {
                io.emit('message', req.session.login + ": " + msg);
                console.log(req.session.login + ": " + msg);
            });

            //logout
            socket.on('logout', () => {
                socket.emit('logging out');
                req.session.destroy();
            });
        });
    }
    else {
        res.redirect('/');
    }
});