> Symfony 7 > Dependency Injection #[Attributes]
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07.

Decorate a Service with AsDecorator

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In the last chapter, we used #[AsAlias] to alias RemoteInterface to ButtonRemote so that when we type-hint RemoteInterface, it gives us the ButtonRemote service. But, this broke our logging! We need to tell Symfony to give us LoggerRemote instead, but to pass the ButtonRemote service to LoggerRemote.

#[AsDecorator]

Basically, we need to tell Symfony that ButtonRemote is being decorated by LoggerRemote. To do this, in LoggerRemote, use another attribute: #[AsDecorator] passing in the service it decorates: ButtonRemote::class:

38 lines | src/Remote/LoggerRemote.php
// ... lines 1 - 5
use Symfony\Component\DependencyInjection\Attribute\AsDecorator;
// ... line 7
#[AsDecorator(ButtonRemote::class)]
final class LoggerRemote implements RemoteInterface
// ... lines 10 - 38

This tells Symfony:

Hey, if anything asks for the ButtonRemote service, give them LoggerRemote instead.

Symfony essentially swaps the services and then makes ButtonRemote the "inner" service to LoggerRemote. This solidifies the need for the RemoteInterface we created earlier. If we tried to type-hint ButtonRemote directly, we'd get a type error because Symfony would be trying to inject LoggerRemote.

Service Decoration

So, follow me on this: we autowire RemoteInterface. That's aliased to ButtonRemote, so Symfony tries to give us that. But then, thanks to #[AsDecorator], it swaps that out for LoggerRemote... but passes ButtonRemote to LoggerRemote. In short, AsDecorator allows us to decorate an existing service with another.

Spin back to the app, refresh and... press "volume up". Check the "Logs" profiler panel and... we're logging again!

Multiple Decorators

Using #[AsDecorator] makes it super easy to add multiple decorators. Maybe we want to add a rate limiting decorator to prevent the kids from mashing buttons. We'd just need to create a RateLimitingRemote class that implements RemoteInterface and add #[AsDecorator(ButtonRemote::class)].

#[AsDecorator(ButtonRemote::class)]
class RateLimitingRemote implements RemoteInterface
{
    public function __construct(
        private RateLimiter $rateLimiter,
        private RemoteInterface $inner,
    ) {
    }

    // ...
}

Next: We'll add a custom logging channel and explore "named autowiring"!