Dependency Injection

Dependency injection is a design pattern used in software development to implement inversion of control. In simpler terms, it's the act of providing dependencies for an object during instantiation.

In PHP, dependency injection can be implemented in various ways, including through constructor injection, setter injection and property injection.

DotKernel API, through its dot-dependency-injection package focuses only on constructor injection.


DotKernel API comes out of the box with the dot-dependency-injection package, which provides all we need for injecting dependencies into any object you want.

dot-dependency-injection determines the dependencies by looking at the #[Inject] attribute, added to the constructor of a class. Dependencies are specified as separate parameters of the #[Inject] attribute.

For our example we will inject UserService and config dependencies into a UseHandler.

use Dot\DependencyInjection\Attribute\Inject;

class UserHandler implements RequestHandlerInterface
    public function __construct(
        protected UserServiceInterface $userService,
        protected array $config,
    ) {

If your class needs the value of a specific configuration key, you can specify the path using dot notation: config.example

The next step is to register the class in the ConfigProvider under factories using Dot\DependencyInjection\Factory\AttributedServiceFactory::class

public function getDependencies(): array
    return [
        'factories' => [
            UserHandler::class => AttributedServiceFactory::class

That's it. When your object is instantiated from the container, it will automatically have its dependencies resolved.

Dependencies injection is available to any object within DotKernel API. For example, you can inject dependencies in a service, a handler and so on, simply by registering it in the ConfigProvider.