Entry in database

[harshittpandey]

many people can register with same username.

[Saspect-IO]

That's because there are no params set for username. You can set it to unique in the model schema and drop duplicate. See link below. You can also setup a search function to check the database by username and if input is in database then alert user to enter new username.

https://stackoverflow.com/questions/28649593/how-to-ensure-a-unique-email-username-will-enter-into-mongodb-using-mongoose

[chia7]

Can I use customize express-validator to do that? I've try a few ways but they do not work out. The User.findOne function would not return instantly, cause the registration success.

[Saspect-IO]

You need to use a promise, Try this code below, modified from this link :https://stackoverflow.com/questions/35008433/i-am-using-node-js-promise-for-validating-either-username-exist-in-db-or-not

function findUser() {
  return User.findOne({"username": req.body.username}).then(function(user) {
    if (user.username) {
console.log(user.username);
req.flash('success_msg', 'Username Already Exist, Please Enter a different username');
 res.redirect('/users/register');
      throw new Error('Username already exists!');
    }

    // user doesn't exist, all is good in your case
  }, function(err) {
    // handle mongoose errors here if needed

    // rethrow an error so the caller knows about it
    throw new Error('Some Mongoose error happened!');
    // or throw err; if you want the caller to know exactly what happened
  });
}

Then you call the find user function here.

findUser().then(function() { // user doesn't exist, do your stuff User.createUser(newUser, function(err, user){ f(err){ } }); req.flash('success_msg', 'You are registered and can now login'); res.redirect('/users/login'); }).catch(function(err) { // here, you'll have Mongoose errors or 'User already exists!' error console.log(err.message); });

Really hope this helps