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Manual Service Config in services.yaml


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At your terminal, run:

bin/console debug:container --parameters

One of the kernel parameters is called kernel.debug. In addition to environments, Symfony has this concept of "debug mode". It's true for the dev environment and false for prod. And, occasionally, it comes in handy!

Here's our new challenge (mostly to see if we can do it). Inside of MixRepository, I want to figure out if we're in debug mode. If debug mode is true, we will cache for 5 seconds. If it's false, I want to cache for 60 seconds:

27 lines | src/Service/MixRepository.php
// ... lines 1 - 8
class MixRepository
public function __construct(
// ... lines 12 - 13
private bool $isDebug
) {}
public function findAll(): array
return $this->cache->get('mixes_data', function(CacheItemInterface $cacheItem) {
$cacheItem->expiresAfter($this->isDebug ? 5 : 60);
// ... lines 21 - 23

Dependency Injection!

Let's back up for a minute. Suppose you're working inside of a service like MixRepository. Suddenly you realize that you need some other service like the logger. What do you do to get the logger? The answer: you do the dependency injection dance. You add a private LoggerInterface $logger argument and property... then you use it down in your code. You'll do this tons of times in Symfony.

Let me undo that... because we don't actually need the logger right now. But what we do need is similar. Right now we're inside of a service and we've suddenly realized that we need some configuration (the kernel.debug flag) to do our work. What do we do to get that config? The same thing! Add that as an argument to our constructor. Say private bool $isDebug, and down here, use it: if $this->isDebug, cache for 5 seconds, else cache for 60 seconds.

Non-Autowireable Arguments

But... there's a slight complication... and I bet you already know what it is. When we refresh the page... yikes! We get a Cannot resolve argument error. If you skip a bit, it says:

Cannot autowire service App\Service\MixRepository: argument $isDebug of method __construct() is type-hinted bool, you should configure its value explicitly.

That makes sense. Autowiring only works for services. You can't have a bool $isDebug argument and expect Symfony to somehow realize that we want the kernel.debug parameter. I might be a wizard, but I don't have a spell for that. I can make a whole slice of pie disappear, though. With magic. Definitely.

Configuring MixRepository in services.yaml

How do we fix this? Open a file that we haven't looked at yet: config/services.yaml:

# This file is the entry point to configure your own services.
# Files in the packages/ subdirectory configure your dependencies.
# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices.html#use-parameters-for-application-configuration
# default configuration for services in *this* file
autowire: true # Automatically injects dependencies in your services.
autoconfigure: true # Automatically registers your services as commands, event subscribers, etc.
# makes classes in src/ available to be used as services
# this creates a service per class whose id is the fully-qualified class name
resource: '../src/'
- '../src/DependencyInjection/'
- '../src/Entity/'
- '../src/Kernel.php'
# add more service definitions when explicit configuration is needed
# please note that last definitions always *replace* previous ones

So far, we haven't needed to add any configuration for our MixRepository service. The container saw the MixRepository class as soon as we created it... and autowiring helped the container know which arguments to pass to the constructor. But now that we have a non-autowireable argument, we need to give the container a hint. And we do that in this file.

Head down to the bottom and add the full namespace of this class: App\Service\MixRepository:

29 lines | config/services.yaml
// ... lines 1 - 7
// ... lines 9 - 25
// ... lines 27 - 29

Below that, use the word bind. And below that, give the container a hint to tell it what to pass to the argument by saying $isDebug set to %kernel.debug%:

29 lines | config/services.yaml
// ... lines 1 - 7
// ... lines 9 - 25
'$isDebug': '%kernel.debug%'

I'm using $isDebug on purpose. That needs to exactly match the name of the argument in the class. Thanks to this, the container will pass the kernel.debug parameter value.

And when we try it... it works! The two service arguments are still autowired, but we filled in the one missing argument so that the container can instantiate our service. Nice!

I want to talk more about the purpose of this file and all of the configuration up here. It turns out that a lot of the magic we've been seeing related to services and autowiring can be explained by this code. That's next.