Implementing Domain Events

Overview

Domain events decouple side effects from domain logic. Entities register events during domain methods; use cases publish them after persistence. The Domain layer depends only on contracts (Event, EventBus); the Infrastructure layer provides the Laravel adapter.

Shared Kernel Contracts

Event Marker Interface

declare(strict_types=1);

namespace App\Shared\Domain\Contracts\ServiceBus;

interface Event {}

A pure marker interface — no methods. All domain events implement this contract.

EventBus Contract

declare(strict_types=1);

namespace App\Shared\Domain\Contracts\ServiceBus;

interface EventBus
{
    public function publish(Event ...$events): void;
}

Single method accepting variadic Event arguments. The Domain layer depends on this contract only.

Placement: app/Shared/Domain/Contracts/ServiceBus/

HasDomainEvents Trait

The trait that gives entities event registration and publishing capabilities:

declare(strict_types=1);

namespace App\Shared\Domain;

use App\Shared\Domain\Contracts\ServiceBus\Event;
use App\Shared\Domain\Contracts\ServiceBus\EventBus;

trait HasDomainEvents
{
    /**
     * @var Event[]
     */
    private array $domainEvents = [];

    final public function publishDomainEvents(EventBus $eventBus): void
    {
        $eventBus->publish(...$this->domainEvents);
        $this->domainEvents = [];
    }

    final protected function registerDomainEvent(Event $domainEvent): void
    {
        $this->domainEvents[] = $domainEvent;
    }
}

Key design decisions:

• registerDomainEvent() is final protected — only the entity itself can register events
• publishDomainEvents() is final public — use cases call this after persistence
• Events are cleared after publishing — prevents double-publishing
• Uses variadic unpacking: $eventBus->publish(...$this->domainEvents)

Placement: app/Shared/Domain/HasDomainEvents.php

Domain Event Classes

Event with Entity Payload

The standard pattern — event carries the full entity for listeners to access:

declare(strict_types=1);

namespace App\CustomerRelationshipManagement\Contacts\Domain\Events;

use App\CustomerRelationshipManagement\Contacts\Domain\Contact;
use App\Shared\Domain\Contracts\ServiceBus\Event;
use Illuminate\Broadcasting\InteractsWithSockets;
use Illuminate\Queue\SerializesModels;

final class ContactCreated implements Event
{
    use InteractsWithSockets;
    use SerializesModels;

    public function __construct(public Contact $contact) {}
}

Event with Scalar ID Payload

Used for deletion events — the entity is about to be destroyed, so pass only the ID:

declare(strict_types=1);

namespace App\CustomerRelationshipManagement\Contacts\Domain\Events;

use App\Shared\Domain\Contracts\ServiceBus\Event;
use Illuminate\Broadcasting\InteractsWithSockets;

final class ContactDeleted implements Event
{
    use InteractsWithSockets;

    /**
     * @param string $contact The deleted contact uuid
     */
    public function __construct(public string $contact) {}
}

Rules:

• Always final class — events are immutable facts
• Always implements Event (the Shared Kernel marker interface)
• Constructor uses promoted public properties for the payload
• Entity-carrying events use SerializesModels — enables queue serialization of Eloquent models
• Deletion events use InteractsWithSockets only (no SerializesModels — there's no model to serialize)
• Naming: {Entity}{PastTenseVerb} — e.g., ContactCreated, VisaActivated, UserDeleted, DocumentUploaded
• Placement: {Module}/Domain/Events/

Payload Guidelines

Scalar ID variation also works for events where the listener only needs the identifier (e.g., AccountInvitationAccepted carrying string $invitationId).

Event Registration on Entities

Events are registered during domain methods — never published directly by entities.

In static new() — Creation

public static function new(array $attributes = []): self
{
    $contact = new self($attributes);
    $contact->registerDomainEvent(new ContactCreated($contact));

    return $contact;
}

In toBeDeleted() — Deletion

public function toBeDeleted(): self
{
    $this->registerDomainEvent(new ContactDeleted($this->id));

    return $this;
}

In Domain Methods — Updates and State Transitions

public function updateName(string $first, string $last): self
{
    $this->forceFill([
        'first_name' => $first,
        'last_name' => $last,
    ]);

    $this->registerDomainEvent(new ContactNameUpdated($this));

    return $this;
}

Conditional Registration

Register events only when state actually changes:

public function updateEmail(string $email): self
{
    if ($email !== $this->email) {
        $this->forceFill(['email' => $email]);
        $this->registerDomainEvent(new UserEmailUpdated($this));
    }

    return $this;
}

See the implementing-domain-entities skill for the full entity patterns.

Event Publishing in Use Cases

Use cases publish events after persistence — this ensures events reflect committed state:

declare(strict_types=1);

namespace App\CustomerRelationshipManagement\Contacts\Application;

use App\CustomerRelationshipManagement\Contacts\Domain\Contact;
use App\CustomerRelationshipManagement\Contacts\Domain\Contracts\ContactRepository;
use App\Shared\Domain\Contracts\ServiceBus\EventBus;

final readonly class CreateContact
{
    public function __construct(
        private ContactRepository $repository,
        private EventBus $eventBus,
    ) {}

    public function __invoke(array $attributes): Contact
    {
        $contact = $this->repository->save(Contact::new($attributes));
        $contact->publishDomainEvents($this->eventBus);

        return $contact;
    }
}

The publishing flow:

1. Entity registers events during domain methods (registerDomainEvent())
2. Use case persists the entity via repository ($repository->save())
3. Use case publishes events ($entity->publishDomainEvents($this->eventBus))
4. IlluminateEventBus dispatches events through Laravel's event() helper
5. Registered listeners handle side effects (see implementing-event-handlers)

Rules:

• Always publish after $repository->save() — never before
• Use cases inject EventBus via constructor
• The entity's publishDomainEvents() clears the event queue after dispatching
• For deletion: publish before calling $repository->delete() (the entity still exists at that point)

IlluminateEventBus Adapter

The Infrastructure adapter that bridges domain events to Laravel's event system:

declare(strict_types=1);

namespace App\Shared\Infrastructure\ServiceBus;

use App\Shared\Domain\Contracts\ServiceBus\Event;
use App\Shared\Domain\Contracts\ServiceBus\EventBus;

class IlluminateEventBus implements EventBus
{
    public function publish(Event ...$events): void
    {
        if (empty($events)) {
            return;
        }

        event(...$events);
    }
}

Key points:

• Thin adapter — delegates to Laravel's event() helper
• Guards against empty event arrays
• Framework coupling boundary: The Domain depends on Event + EventBus contracts only. IlluminateEventBus is Infrastructure. This keeps the Domain pure
• Bound in SharedServiceProvider via $bindings array (see configuring-bounded-contexts):

public array $bindings = [
    EventBus::class => IlluminateEventBus::class,
];

Placement: app/Shared/Infrastructure/ServiceBus/IlluminateEventBus.php

Complete Event Flow

Entity                    Use Case                 Infrastructure
──────                    ────────                 ──────────────
registerDomainEvent()  →  $repository->save()   →  Database write
                          publishDomainEvents()  →  IlluminateEventBus::publish()
                                                 →  Laravel event() helper
                                                 →  Registered listeners
                                                 →  domainEvents[] cleared

Common Mistakes

Pre-flight Checklist

• Event marker interface exists in Shared/Domain/Contracts/ServiceBus/?
• EventBus contract defines publish(Event ...$events): void?
• HasDomainEvents trait in Shared/Domain/ with registerDomainEvent() + publishDomainEvents()?
• Domain events are final class implementing Event?
• Entity-carrying events use SerializesModels?
• Deletion events carry scalar ID, not entity?
• Events named as {Entity}{PastTenseVerb}?
• Events placed in {Module}/Domain/Events/?
• Use cases publish events AFTER persistence?
• IlluminateEventBus adapter bound in SharedServiceProvider?

Laravel Reference

This skill uses Laravel-specific features. Consult the official Laravel documentation (via Context7 or web search) for details on:

• event() helper — dispatching events through Laravel's event system
• Illuminate\Queue\SerializesModels — queue-safe serialization of Eloquent models in events
• Illuminate\Broadcasting\InteractsWithSockets — WebSocket broadcasting support for events
• Event::listen() — registering event listeners in service providers
• ShouldQueue — marking event listeners for async processing