Design Patterns In Laravel

Laravel follows several design patterns to ensure code maintainability, scalability, reuseablitity and efficiency. Here are some of the design patterns used in PHP Laravel:

1. MVC (Model-View-Controller):

Laravel follows the MVC pattern, which separates business logic (Model), presentation (View), and request handling (Controller).

2. Repository Pattern:

Used to abstract the data layer and make database queries reusable and independent of the framework. This pattern helps in separating database queries from controllers. for example:

interface UserRepositoryInterface {
    public function getAllUsers();
}

class UserRepository implements UserRepositoryInterface {
    public function getAllUsers() {
        return User::all();
    }
}

In controller

class UserController {
    private $userRepository;

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

    public function index() {
        $users = $this->userRepository->getAllUsers();
        return view('users.index', compact('users'));
    }
}

3. Service Pattern:

In this patterns all the business logic from controllers are moved to service classes. For Example:

// Service class
class UserService {
    public function createUser($data) {
        return User::create($data);
    }
}

// In Controller: 
class UserController {
    private $userService;

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

    public function store(Request $request) {
        $this->userService->createUser($request->all());
        return redirect()->back();
    }
}

4. Dependency Injection:

Laravel injects dependencies into classes instead of creating them manually.

class UserController {
    public function __construct(public UserService $userService) {}
}

5. Singleton Pattern:

Used when a class should have only one instance throughout the application. This pattern is mostly used in laravel facades and service providers. For Example:

class Logger {
    private static $instance;

    private function __construct() {}

    public static function getInstance() {
        if (!self::$instance) {
            self::$instance = new Logger();
        }
        return self::$instance;
    }
}

6. Observer Pattern:

Laravel uses Eloquent Observers to listen for model events like creating, updating, deleting. For example:

class UserObserver {
    public function creating(User $user) {
        $user->uuid = Str::uuid();
    }
}
// Registered in AppServiceProvider

public function boot() {
    User::observe(UserObserver::class);
}

7. Strategy Pattern:

Allows defining a family of algorithms and choosing one at runtime. For example Payment Strategies:

interface PaymentStrategy {
    public function pay($amount);
}

class PaypalPayment implements PaymentStrategy {
    public function pay($amount) {
        echo "Paid $amount using PayPal.";
    }
}

class CreditCardPayment implements PaymentStrategy {
    public function pay($amount) {
        echo "Paid $amount using Credit Card.";
    }
}

class PaymentContext {
    private $strategy;

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

    public function executePayment($amount) {
        return $this->strategy->pay($amount);
    }
}

// Usages

$payment = new PaymentContext(new PaypalPayment());
$payment->executePayment(100);

8. Command Pattern:

used for CLI commands

class SendEmails extends Command {
    protected $signature = 'email:send';
    protected $description = 'Send emails to users';

    public function handle() {
        $this->info('Emails sent successfully.');
    }
}

9. Decorator Pattern:

In laravel it is used for request handling(mostly used in middleware to modify the request/response objects). Example:

class VerifyUserMiddleware {
    public function handle($request, Closure $next) {
        if (!$request->user()->verified) {
            return redirect('verify-email');
        }
        return $next($request);
    }
}

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