CQRS Example

Implementing CQRS in a PHP Project

// Command Interface
interface Command {}

// Command Handler Interface
interface CommandHandler {
    public function handle(Command $command): void;
}

// Example Command
class CreateUserCommand implements Command {
    public $userId;
    public $name;
    public $email;

    public function __construct($userId, $name, $email) {
        $this->userId = $userId;
        $this->name = $name;
        $this->email = $email;
    }
}

// Example Command Handler
class CreateUserCommandHandler implements CommandHandler {
    private $userRepository;

    public function __construct(UserRepository $userRepository) {
        $this->userRepository = $userRepository;
    }

    public function handle(Command $command): void {
        $user = new User($command->userId, $command->name, $command->email);
        $this->userRepository->save($user);

        // Publish event to update read model
        EventDispatcher::dispatch(new UserCreatedEvent($command->userId, $command->name, $command->email));
    }
}

// Query Interface
interface Query {}

// Query Handler Interface
interface QueryHandler {
    public function handle(Query $query);
}

// Example Query
class GetUserByIdQuery implements Query {
    public $userId;

    public function __construct($userId) {
        $this->userId = $userId;
    }
}

// Example Query Handler
class GetUserByIdQueryHandler implements QueryHandler {
    private $readRepository;

    public function __construct(ReadRepository $readRepository) {
        $this->readRepository = $readRepository;
    }

    public function handle(Query $query) {
        return $this->readRepository->findById($query->userId);
    }
}

// Event
class UserCreatedEvent {
    public $userId;
    public $name;
    public $email;

    public function __construct($userId, $name, $email) {
        $this->userId = $userId;
        $this->name = $name;
        $this->email = $email;
    }
}

// Event Dispatcher (Simple Implementation)
class EventDispatcher {
    private static $listeners = [];

    public static function addListener($eventClass, callable $listener) {
        self::$listeners[$eventClass][] = $listener;
    }

    public static function dispatch($event) {
        $eventClass = get_class($event);
        if (isset(self::$listeners[$eventClass])) {
            foreach (self::$listeners[$eventClass] as $listener) {
                $listener($event);
            }
        }
    }
}

// Listener to Update Read Model
EventDispatcher::addListener(UserCreatedEvent::class, function(UserCreatedEvent $event) {
    // Update read model with new user data
    $readRepository = new ReadRepository();
    $readRepository->add($event->userId, $event->name, $event->email);
});