Observer Pattern with Events/Listeners

One of the most widely used design patterns in Laravel is Observer.

Actually, there are two Laravel features for this pattern:

• Eloquent Model Observers
• Events / Listeners

The general idea is this:

1. The "main" code is happening in an "active" way: in Controller, for example
2. Then there are other "subscribed" classes observing what happened, waiting to be activated when needed

Event/Listener: Practical Example

Look at a typical Event/Listener example from Laravel Breeze:

app/Http/Controllers/Auth/RegisteredUserController.php:

use Illuminate\Auth\Events\Registered;
 
// ...
 
class RegisteredUserController extends Controller
{
    public function store(Request $request): RedirectResponse
    {
        // ... validation
 
        $user = User::create([
            'name' => $request->name,
            'email' => $request->email,
            'password' => Hash::make($request->password),
        ]);
 
        event(new Registered($user)); 

The registration Controller fires the event Registered that can be listened to by others.

Inside that Registered Event class, which comes from Laravel core, we have $user as a property.

Illuminate/Auth/Events/Registered.php:

use Illuminate\Queue\SerializesModels;
 
class Registered
{
    use SerializesModels;
 
    public $user;
 
    public function __construct($user)
    {
        $this->user = $user;
    }
}

And then, for example, we want to create a listener to auto-create a Team for that new user.

Then, all we need to do:

• Generate the Listener with php artisan make:listener CreateTeamListener
• Pass the Registered Event as a parameter, and the Listener will auto-listen for that Event

app/Listeners/CreateTeamListener.php:

use App\Models\Team;
use Illuminate\Auth\Events\Registered;
 
// ...
 
class CreateTeamListener
{
    public function handle(Registered $event): void
    {
        // Access the user using $event->user...
        Team::create([
            'name' => $event->user->name . "'s Team",
            'user_id' => $event->user->id,
        ]);
    }
}

With recent Laravel changes, we don't even need to register that Listener anywhere. The event discovery will take care of it.

Observer Example: The Same Pattern?

Eloquent Observers just happens to be a more convenient "wrapper" implementation of events/listeners.

For example...