CODESAMPLE

Dependency Injection - PHP

Dependency Injection PHP

Dependency Injection (DI) is a design pattern where a class receives its dependencies from external sources rather than creating them itself. This promotes loose coupling, making the class more testable, reusable, and maintainable. Our example demonstrates Constructor Injection, a common DI technique. The UserController requires a UserRepository to function, but instead of instantiating UserRepository within UserController, it receives a pre-configured instance through its constructor. This allows us to easily swap out different UserRepository implementations (e.g., a Mock for testing) without modifying UserController. This approach aligns with PHP’s principles of separation of concerns and is often leveraged with Dependency Injection Containers (though not explicitly used here for simplicity).

<?php

interface UserRepository
{
    public function getUser(int $id): ?User;
}

class User
{
    private int $id;
    private string $name;

    public function __construct(int $id, string $name)
    {
        $this->id = $id;
        $this->name = $name;
    }

    public function getId(): int
    {
        return $this->id;
    }

    public function getName(): string
    {
        return $this->name;
    }
}

class UserController
{
    private UserRepository $userRepository;

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

    public function show(int $id): ?User
    {
        return $this->userRepository->getUser($id);
    }
}

class RealUserRepository implements UserRepository
{
    public function getUser(int $id): ?User
    {
        // Simulate fetching from a database
        if ($id == 1) {
            return new User(1, "John Doe");
        }
        return null;
    }
}

// Usage:
$userRepository = new RealUserRepository();
$userController = new UserController($userRepository);
$user = $userController->show(1);

if ($user) {
    echo "User ID: " . $user->getId() . ", Name: " . $user->getName() . "\n";
} else {
    echo "User not found.\n";
}

?>