req.session is undefined nodeJS - node.js

Question

im trying to set up a session in NodeJS and use it in my /auth route after that but i'm getting undefined troubles with the session.
In the app.js :
const express = require('express'),
path = require('path'),
bodyParser = require('body-parser'),
cors = require('cors'),
mongoose = require('mongoose'),
config = require('./config/DB');
const app = express();
const session = require('express-session')
const MongoStore = require('connect-mongo')(session);
mongoose.connect(config.DB, { useNewUrlParser: true }).then(
() => { console.log('Database is connected') },
err => { console.log('Can not connect to the database' + err) },
options
);
const db = mongoose.connection
const adUnitRoutes = require('./routes/adunit.route');
const userProfileRoutes = require('./routes/userprofile.route');
app.use('/adunits', adUnitRoutes);
app.use('/userprofile', userProfileRoutes);
app.use(session({
secret: 'my-secret',
resave: false,
saveUninitialized: true,
store: new MongoStore({ mongooseConnection: db })
}));
In the route :
userProfileRoutes.route('/authentification').post((req, res) => {
console.log('req session : ' + req.session.userId);
//here I got cant read property of userId because session is undefined
});

Answer 1

This happens because you are setting your routes before adding the middleware. Your handlers are essentially middleware so if they are added before session, your session has not been processed and added to the request yet.
Adding the routes after setting your middleware will make it work as expected.
See this minimized example:
const express = require('express');
const app = express();
const session = require('express-session');
app.get('/broken', (req, res) => {
console.log('req session : ' + req.session.userId);
res.write(String(req.session.userId));
req.session.userId = 1;
res.end();
});
app.use(
session({
secret: 'my-secret',
resave: false,
saveUninitialized: true
})
);
app.get('/ok', (req, res) => {
console.log('req session : ' + req.session.userId);
res.write(String(req.session.userId));
req.session.userId = 1;
res.end();
});
app.listen(8089);