How Laravel uses Dependency Injection.
Jul 30, 2025 am 05:22 AM
Laravel uses dependency injection (DI) to enhance flexibility and testability by letting classes receive dependencies from outside. 1. DI in Laravel is commonly seen in controllers, jobs, and events, where dependencies are automatically resolved. 2. Type-hinting a class in a controller method like public function show(User $user) allows Laravel to inject the dependency automatically, including route model binding. 3. Constructor injection, such as in UserController, decouples dependency creation from usage, easing testing and reuse. 4. Laravel’s service container resolves dependencies automatically by analyzing constructors, building the object graph without manual instantiation. 5. Interfaces can be bound to implementations via service providers using $this->app->bind(). 6. Use DI for better testability, decoupling, and reusable code. 7. Method injection, like public function store(Request $request), works for common types such as Request. 8. Dependencies can also be manually resolved using app() or resolve().
Laravel uses dependency injection (DI) to manage class dependencies and make your application more flexible and testable. At its core, DI means a class doesn’t create its own dependencies — they’re given to it from the outside. Laravel’s service container handles this automatically, so you don’t have to wire everything up manually.
What Dependency Injection Looks Like in Laravel
In Laravel, you’ll most often see dependency injection in controllers, jobs, events, and other classes that the framework resolves automatically.
For example, if you type-hint a class in a controller method like this:
public function show(User $user)
Laravel will automatically resolve the User model from the container and inject it for you. It even does this for route model binding — if the route parameter is a model type, Laravel fetches the instance from the database automatically.
You’ll also see it in constructor injection:
class UserController extends Controller
{
protected $userRepository;
public function __construct(UserRepository $userRepository)
{
$this->userRepository = $userRepository;
}
}Here, the UserController doesn’t care how the UserRepository is built — it just needs to use it. That makes the controller easier to test and more flexible.
How Laravel’s Service Container Works
Laravel’s service container is a powerful tool that manages class dependencies and resolves them automatically. When you ask for a class — either through type-hinting or manually with app() or resolve() — the container looks at that class’s constructor and figures out what it needs.
If all dependencies are type-hinted, Laravel can build the entire object graph for you. For example:
$api = new TwitterApi('api-key');
$client = new TwitterClient($api);
$service = new TweetService($client);Instead of doing this manually, you can just type-hint TweetService and Laravel will resolve everything under the hood.
Sometimes you need to bind an interface to a concrete implementation. That’s where service providers and bindings come in:
$this->app->bind(
'App\Contracts\TwitterApi',
'App\Services\TwitterClient'
);Now whenever Laravel needs a TwitterApi, it knows to use TwitterClient.
When to Use Dependency Injection in Your Code
Use DI when:
- You want your code to be testable — by injecting dependencies, you can easily swap them out for mocks.
- You want to decouple your classes — if a class creates its own dependencies, it becomes harder to reuse or modify later.
- You’re building reusable services or packages — DI makes it easier for others to override or extend your code.
You don’t always need to use constructor injection. Laravel supports method injection too — especially useful in controllers:
public function store(Request $request)
Here, the Request object is injected into the method, not the constructor. Laravel handles this because it knows how to resolve common types like Request, Session, etc.
You can also manually resolve things from the container using app() or resolve():
$tweetService = app(TweetService::class);
This is handy in places like routes or closures where automatic injection isn’t possible.
That’s the basic idea. Laravel makes dependency injection easy by handling most of the wiring for you, as long as you follow the patterns it expects. Just type-hint what you need, and let the container do the rest.
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