Dependency Injection in PHP (Simple and Practical)

Dependency Injection (DI) means: instead of creating dependencies inside a class, you pass them in. This makes code: - easier to test - easier to change later - more professional ## Bad (hard to test) ```php class OrdersService { public function createOrder() { $pdo = new PDO("..."); // hard to test because DB is inside } } ``` ## Good (inject dependency) ```php class OrdersService { public function __construct(private PDO $pdo) {} public function createOrder() { // use $this->pdo } } ``` ## Why this is better ```mermaid flowchart LR A[Controller] --> B[OrdersService] B --> C[(PDO DB)] ``` Now in tests you can inject a fake PDO or a mock wrapper. > Next: PHP exceptions, custom exceptions, and clean error responses.