Clean Architecture in PHP Projects

In the fast-paced world of web development, PHP continues to be one of the most powerful and widely used backend technologies. However, as projects grow in size and complexity, maintaining code quality, readability, and scalability becomes a major challenge. This is where Clean Architecture comes into play.

Clean Architecture is not just a buzzword — it’s a way of structuring your PHP applications to ensure they remain modular, testable, and easy to maintain over time. In this blog, we’ll explore what Clean Architecture is, why it matters, and how you can effectively implement it in your PHP projects in 2025 and beyond.

What Is Clean Architecture?

Clean Architecture is a software design philosophy introduced by Robert C. Martin (Uncle Bob). Its goal is to create systems that are independent of frameworks, databases, UI layers, and external agencies — making them easier to change, test, and maintain.

At its core, Clean Architecture emphasizes separation of concerns by dividing your application into distinct layers, each with a specific purpose. The most important principle is dependency inversion, which means that outer layers depend on inner layers — never the other way around.

The Core Principles of Clean Architecture

Before diving into PHP-specific examples, let’s understand the fundamental principles that make up Clean Architecture:

1. Separation of Concerns

Each part of the application should have one clear responsibility. The business logic should not be tangled with presentation or database logic.

2. Dependency Rule

The inner layers should never depend on the outer layers. Instead, dependencies flow inward, which means high-level policies dictate how low-level components behave.

3. Testability

Because of the clear separation between logic and infrastructure, testing becomes much easier. You can test your business rules without relying on the database or external systems.

4. Framework Independence

Your app should not be tightly coupled with a specific framework (like Laravel or Symfony). Frameworks should be treated as tools — not the foundation of your system.

5. Database and UI Independence

Your business logic should not care whether you use MySQL, MongoDB, or Redis — or whether your frontend is in Vue.js, React, or plain HTML.

The Clean Architecture Layers

Clean Architecture typically consists of four concentric layers:

1. Entities (Core Business Logic)

2. Use Cases (Application Logic)

3. Interface Adapters (Controllers, Presenters, Gateways)

4. Frameworks and Drivers (External Tools like Databases, APIs, UI)

Let’s look at how these layers map to a PHP application.

Entities (Domain Layer)

This layer holds the business rules of your application. These are pure PHP classes that represent real-world concepts.

Example:

class Order {
    private float $amount;
    private bool $isPaid = false;

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

    public function pay(): void {
        $this->isPaid = true;
    }

    public function isPaid(): bool {
        return $this->isPaid;
    }
}

This class is framework-independent and can be tested without any external dependency.

Use Cases (Application Layer)

This layer defines the actions that can be performed using the business rules — essentially your application’s core behavior.

Example:

class PayOrder {
    public function execute(Order $order): void {
        $order->pay();
    }
}

This layer uses entities to perform specific operations but doesn’t know how data is stored or presented.

Interface Adapters (Infrastructure Layer)

This layer adapts the external world to the inner layers. It includes controllers, presenters, and repositories.

Example Repository Interface:

interface OrderRepository {
    public function save(Order $order): void;
    public function findById(int $id): ?Order;
}

Example Controller:

class OrderController {
    public function __construct(private PayOrder $payOrder, private OrderRepository $repository) {}

    public function pay(int $orderId) {
        $order = $this->repository->findById($orderId);
        if ($order) {
            $this->payOrder->execute($order);
            $this->repository->save($order);
        }
    }
}

Frameworks and Drivers (External Layer)

This outermost layer deals with frameworks, tools, and delivery mechanisms like HTTP requests, databases, and CLI commands.

In a Laravel or Symfony project, this layer would include controllers, routes, Eloquent models, and service providers. However, none of these should contain core business logic — they should only serve as entry points.

Implementing Clean Architecture in PHP

Let’s walk through a practical approach to applying Clean Architecture in a PHP project.

Step 1: Organize Your Directory Structure

A clean and meaningful directory structure helps enforce the architecture:

src/
 ├── Domain/
 │    ├── Entities/
 │    └── Repositories/
 ├── Application/
 │    ├── UseCases/
 ├── Infrastructure/
 │    ├── Persistence/
 │    └── Http/
 └── Framework/
      ├── Laravel/
      ├── Symfony/

Each layer is isolated, making it easy to change one without affecting others.

Step 2: Use Dependency Injection

Dependency Injection (DI) ensures that dependencies are passed into classes instead of being created inside them. PHP frameworks like Laravel and Symfony make DI easy with their service containers.

Example:

$orderRepository = new MySqlOrderRepository();
$payOrder = new PayOrder();
$controller = new OrderController($payOrder, $orderRepository);

This approach makes the system modular and testable.

Step 3: Abstract Infrastructure

Avoid coupling business logic with implementation details. Use interfaces to abstract external services like databases, mailers, or APIs.

For example, instead of directly calling a Mail::send() function, create a MailerInterface that your application can depend on.

Step 4: Add Unit and Integration Tests

With Clean Architecture, writing tests becomes natural. You can test your use cases in isolation without worrying about the database or HTTP layer.

Example:

$useCase = new PayOrder();
$order = new Order(100);
$useCase->execute($order);
assert($order->isPaid() === true);

Step 5: Keep Framework Code at the Edges

The framework should act as a delivery mechanism — not as the core of your application. This ensures you can switch frameworks or even run the same business logic from the command line, API, or cron job.

Benefits of Clean Architecture in PHP

1. Maintainability – Each layer is independent, making it easier to modify or replace components.

2. Testability – Pure business logic can be tested without worrying about external dependencies.

3. Scalability – The system can grow without becoming tightly coupled.

4. Framework Flexibility – You can upgrade or migrate frameworks with minimal impact on the core logic.

5. Code Readability – The structure clearly communicates the purpose of each component.

Common Mistakes to Avoid

• Mixing database logic with controllers.

• Using framework models directly inside your domain layer.

• Writing business rules inside routes or views.

• Over-engineering small projects — Clean Architecture is best for medium to large applications.

Conclusion

Clean Architecture gives PHP developers the power to write code that’s elegant, maintainable, and scalable. By separating concerns and organizing your project into distinct layers, you make it easier to test, extend, and understand.

In 2025, as PHP continues to evolve with modern practices and tools, Clean Architecture stands out as a timeless approach to building strong, future-proof applications. Whether you’re working with Laravel, Symfony, or a custom PHP framework, embracing Clean Architecture ensures your project stays robust, modular, and ready for whatever comes next.