Saving User to MongoDB

Saving User to MongoDB

Now let us connect the Passport callback to the database. When a user logs in, you should check if they already exist. If they do, use the existing record. If not, create a new one.

Updated Passport Callback

// config/passport-setup.js
const passport = require('passport');
const GoogleStrategy = require('passport-google-oauth20').Strategy;
const keys = require('./keys');
const User = require('../models/user-model');

passport.use(
    new GoogleStrategy({
        clientID: keys.google.clientID,
        clientSecret: keys.google.clientSecret,
        callbackURL: '/auth/google/redirect'
    }, function(accessToken, refreshToken, profile, done) {
        // Check if user already exists
        User.findOne({ googleId: profile.id }).then(function(currentUser) {
            if (currentUser) {
                // User exists — use existing record
                console.log('User already exists:', currentUser);
                done(null, currentUser);
            } else {
                // User does not exist — create new
                new User({
                    username: profile.displayName,
                    googleId: profile.id,
                    thumbnail: profile.photos[0].value
                }).save().then(function(newUser) {
                    console.log('New user created:', newUser);
                    done(null, newUser);
                });
            }
        });
    })
);

The Logic Flow

Passport callback fires with Google profile
    ↓
Search database for googleId
    ↓
┌─── Found? ──────────────────────┐
│ YES: Use existing user          │
│ NO:  Create new user, save to DB│
└─────────────────────────────────┘
    ↓
Call done(null, user)
    ↓
Passport continues with session setup

What Gets Stored in MongoDB

{
    "_id": "5a1b2c3d4e5f6g7h8i9j",
    "username": "Shaun Pelling",
    "googleId": "123456789012345678901",
    "thumbnail": "https://lh3.googleusercontent.com/photo.jpg",
    "__v": 0
}

Key Takeaways

• Always check if the user exists before creating a new record
• Use googleId to identify returning users — it is unique per Google account
• Call done(null, user) with the user object (new or existing) to continue the flow
• First login creates a record; subsequent logins find and reuse it