Best way to validate uniqueness of a field Mangoose Node - node.js

Question

When registering a new user, I want to check email for uniqueness. I am using body parser to make sure all fields are not empty, but how am I to check that the input email is not used by anyone else and to immediately output the message for a user?
The technology stack is Node.js, mongoose, body-parser module, mongodb
Here's the route file:
router.post('/register', function(req, res){
let name = req.body.name;
let email = req.body.email;
req.checkBody('name', 'Name field is empty!').notEmpty();
req.checkBody('email', 'Email field is empty!').notEmpty();
req.checkBody('email', 'Invalid email format').isEmail();
var errors = req.validationErrors();
if(errors){
res.render('register', {
errors:errors
});
} else {
let newUser = new User({
name: name,
email: email
});
After looking through similar questions, I found a way to use a pre save in my model file, but I don't know how to sisplay the error to the user as a part of the errors array (see above)
Any help will be highly appreciated!

Answer 1

You can achieve both from the Mongoose model and the Register() method.
The user model should be like this:
var mongoose = require('mongoose');
var UserSchema = new mongoose.Schema({
email: {
type: String,
lowercase: true,
unique: true,
sparse: true
},
password: {
type: String,
required: true
},
},
{
timestamps: true
});
module.exports = mongoose.model('User', UserSchema);
This will ensure that emails are unique. Then at the register method, you do this:
exports.register = function(req, res, next){
let name = req.body.name;
let email = req.body.email;
User.findOne({email: email}, function(err, existingUser){
if(err){
return res.status(500).json(err);
}
if(existingUser){
return res.status(422).json('Email address is already registered.');
}
else {
var user = new User({
username : username,
email: email,
password: password
});
user.save(function(err, user){
if(err){
return next(err);
}
var userInfo = setUserInfo(user);
res.status(201).json({
token: 'JWT ' + generateToken(userInfo),
user: userInfo
})
});
}
});
}
}
}
Hope this helps.