Building a Referral System with Laravel

I recently launched a small product for Amazon Affiliates built with Laravel. At the heart of the application is a referral system. Users get bonus credits when they refer another user while getting recurring credit every time their referral uses the site. To tackle this the Laravel way, I got to use Requests, Middleware, and Cookies. I also integrated Google login using Socialite but that's another post entirely. _

Side Note For Context: Since Amazon Affiliates cannot use their own affiliate codes for purchases they make themselves, I built Associate Swap.

When you search Swap for Amazon products it will grab a random Affiliate code from the database and add it to the URL. The more you use swap and refer other affiliates to swap the greater chance your code will be picked. The referral system is the heart of the growth and retention model._

Referral Use Case When a user signs up, they are automatically generated a unique affiliate_id. This id is will be used to generate unique URLs they can share to be credited for another user signing up and using the site - ie https://associateswap.com/?ref=17FbCjzIzj. Getting Started I'm going to assume you've already scaffolded your Authentication using the make:auth artisan command.

$ php artisan make:auth

Using this command you will now have a User model and associated Migrations. In order to track who referred who we need to add a couple of fields to our User object and associated database table. Time to generate a Migration.

$ php artisan make:migration AddAffiliateTrackingToUsersTable

Open up the migration file that was just generated, and add the fields we need to track users in the referral system.

<?php

use Illuminate\\Support\\Facades\\Schema;
use Illuminate\\Database\\Schema\\Blueprint;
use Illuminate\\Database\\Migrations\\Migration;

class AddAffiliateTrackingToUsersTable extends Migration
{
    /\*\*
     \* Run the migrations.
     \*
     \* @return void
     */
    public function up()
    {
        Schema::table('users', function(Blueprint $table)
        {
            $table->string('referred_by')->nullable();
            $table->string('affiliate_id')->unique();
        });
    }

    /\*\*
     \* Reverse the migrations.
     \*
     \* @return void
     */
    public function down()
    {
        Schema::table('users', function(Blueprint $table)
        {
            $table->dropColumn('referred_by');
            $table->dropColumn('affiliate_id');
        });
    }
}

Now is a good time to run the Migrations on your database... If you haven't run this since make:auth then it will create the User Model and Table. And with your additional Migration it will add your new fields referred_by and affiliate_id.

$ php artisan migrate

If you stop reading now and skip ahead you are going to run into an annoying error. If you jump to the Cookie generation and the Middleware part of the post (I mean c'mon who can't wait until the Middleware section) you are going to bypass a commonly missed Laravel step. Update your model to make your new fields fillable which I've forgotten on every project. That should look something like this...

<?php

namespace App;

use Illuminate\\Notifications\\Notifiable;
use Illuminate\\Foundation\\Auth\\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    /\*\*
     \* The attributes that are mass assignable.
     \*
     \* @var array
     */
    protected $fillable = \[
        'name', 'email', 'password', 'affiliate\_id', 'referred\_by',
    \];

    /\*\*
     \* The attributes that should be hidden for arrays.
     \*
     \* @var array
     */
    protected $hidden = \[
        'password', 'remember_token',
    \];
}

Cool. Now what? Now we need to generate that new affiliate_id when someone registers on the site. You probably have a file called RegisterController that make:auth scaffolds for you. In there should be a create method which you'll want to change to auto generate an affiliate code for that user.

protected function create(array $data) {
    return User::create(\[
        'email' => $data\['email'\],
        'password' => bcrypt($data\['password'\]),
        'affiliate\_id' => str\_random(10),
    \]);
}

For brevity, we've just updated this to generate a random string for the affiliate_id field. This has a unique database constraint but you should probably do layer of validation here. If it was me I'd built an affiliate id helper function to generate a suitably unique string here that doesn't toss a DB constraint error in your user's faces. Just sayin. Alright now we are rolling - now how do we track when someone uses your code to register? Here's where it starts getting fun. We want to give the referrer credit when someone uses their unique URL in registration. First off - we need to tell them what URL to share. Lets update a Blade template.

@if(!Auth::user()->affiliate_id)
    <input type="text" readonly="readonly" 
           value="{{url('/').'/?ref='.Auth::user()->affiliate_id}}">
@endif

Now your user can copy and paste the URL they need to share to get credit. You've reached the fun part. It's time to play with Laravel Middleware.

Middleware provide a convenient mechanism for filtering HTTP requests entering your application. For example, Laravel includes a middleware that verifies the user of your application is authenticated. If the user is not authenticated, the middleware will redirect the user to the login screen. However, if the user is authenticated, the middleware will allow the request to proceed further into the application.

Scaffolding a Middleware is another handy artisan command.

$ php artisan make:middleware CheckReferral

The CheckReferral middleware's job is to inspect every HTTP request to the application to see if it has the ?ref query string in the URL. In a more complex application this would allow your referrer to link a potential signup to any URL on the site (whether it be your signup page, pricing page, homepage, etc).

<?php

namespace App\\Http\\Middleware;

use Illuminate\\Http\\Response;
use Closure;

class CheckReferral
{
    /\*\*
     \* Handle an incoming request.
     \*
     \* @param  \\Illuminate\\Http\\Request  $request
     \* @param  \\Closure  $next
     \* @return mixed
     */
    public function handle($request, Closure $next)
    {
        if( $request->hasCookie('referral')) {
            return $next($request);
        }
        else {
            if( $request->query('ref') ) {
                return redirect($request->fullUrl())->withCookie(cookie()->forever('referral', $request->query('ref')));
            }
        }

        return $next($request);
    }
}

There's an affiliate industry standard of persisting referrals in a cookie so there's an increased chance of getting credit for the conversion. For Amazon Affiliates, the cookie expires in 24 hours. For Associate Swap it's a forever cookie. First step in the Middleware code above is to check if the cookie already exists and move on returning the Request if it does. If the cookie doesn't already exist but the ref parameter exists in the query string we return the Request object as normal while attaching our referral Cookie to it.

Side Note: Building Middleware in Laravel is an excellent example of utilizing the simplicity of the Laravel Service Container - ie dependency injection._ We aren't done yet, though. The referrer is still not getting credit. Back to the RegisterController.

<?php

namespace App\\Http\\Controllers\\Auth;

use DB;
use App\\User;
use App\\Http\\Controllers\\Controller;
use Illuminate\\Support\\Facades\\Validator;
use Illuminate\\Foundation\\Auth\\RegistersUsers;
use Cookie;

class RegisterController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Register Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles the registration of new users as well as their
    | validation and creation. By default this controller uses a trait to
    | provide this functionality without requiring any additional code.
    |
    */

    use RegistersUsers;

    /\*\*
     \* Where to redirect users after registration.
     \*
     \* @var string
     */
    protected $redirectTo = '/home';

    /\*\*
     \* Create a new controller instance.
     \*
     \* @return void
     */
    public function __construct()
    {
        $this->middleware('guest');
    }

    /\*\*
     \* Get a validator for an incoming registration request.
     \*
     \* @param  array  $data
     \* @return \\Illuminate\\Contracts\\Validation\\Validator
     */
    protected function validator(array $data)
    {
        return Validator::make($data, \[
            'email' => 'required|email|max:255|unique:users',
            'password' => 'required|min:6|confirmed',
            'tracking_id' => 'required'
        \]);
    }

    /\*\*
     \* Create a new user instance after a valid registration.
     \*
     \* @param  array  $data
     \* @return User
     */
    protected function create(array $data)
    {
        $referred_by = Cookie::get('referral');

        return User::create(\[
            'email' => $data\['email'\],
            'password' => bcrypt($data\['password'\]),
            'affiliate\_id' => str\_random(10),
            'referred\_by'   => $referred\_by
        \]);
    }
}

Now when we create the user in RegistrationController we check for that Cookie. If it has a value it gets inserted into our database. Otherwise the column gets a null value as we determined in our original migration. Your use case might award affiliates differently so I wont go into details on how credits are applied on Associate Swap. But now you can track if a user was referred by another user. If you are using Laravel Cashier you may hook into a Stripe Webhook to pay out an affiliate in realtime after a sale is made by someone they referred. For me it was simply incrementing a counting mechanism every time they perform an action in the web application.