Mongodb database collection not updating unless server restarted

Question

Whenever a user follows some other user the userCollection is not updating unless server is restarted but in the mongo console the changes are shown even without restarting server.server.js is something like this-

var db=require('./database.js');
app.post('/addFollower',function(req,res){
    console.log(req.user);
    db.then(function(data){
           var userCollection=data.collection('users');
           userCollection.update({"username":req.user.username},{$addToSet:{"following":req.body.followWho}}, )
              userCollection.update({"username":req.body.followWho},{$addToSet:{"followers":req.user.username}})
                console.log("User followed")   ;
                console.log(req.user)
                  db=require('./database.js');    
                res.redirect('/posts')
})
})

I have console.log(req.user) before and after updation but it shows the same object.But in mongo console the req.user object is updated.Why is that? database.js

var mongodb=require('mongodb');
var MongoClient=mongodb.MongoClient;
var url='mongodb://localhost:27017/imageDatabase';

function getDb(){

    return MongoClient.connect(url).then(function (db) {
        // console.log(MongoClient.connect(url));
        return db;
    })
}

module.exports=getDb();