How to Configure a Service with a Configurator

The service configurator is a feature of the service container that allows you to use a callable to configure a service after its instantiation.

A service configurator can be used, for example, when you have a service that requires complex setup based on configuration settings coming from different sources/services. Using an external configurator, you can maintain the service implementation cleanly and keep it decoupled from the other objects that provide the configuration needed.

Another use case is when you have multiple objects that share a common configuration or that should be configured in a similar way at runtime.

For example, suppose you have an application where you send different types of emails to users. Emails are passed through different formatters that could be enabled or not depending on some dynamic application settings. You start defining a NewsletterManager class like this:

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// src/AppBundle/Mail/NewsletterManager.php
namespace AppBundle\Mail;

class NewsletterManager implements EmailFormatterAwareInterface
{
    private $enabledFormatters;

    public function setEnabledFormatters(array $enabledFormatters)
    {
        $this->enabledFormatters = $enabledFormatters;
    }

    // ...
}

and also a GreetingCardManager class:

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// src/AppBundle/Mail/GreetingCardManager.php
namespace AppBundle\Mail;

class GreetingCardManager implements EmailFormatterAwareInterface
{
    private $enabledFormatters;

    public function setEnabledFormatters(array $enabledFormatters)
    {
        $this->enabledFormatters = $enabledFormatters;
    }

    // ...
}

As mentioned before, the goal is to set the formatters at runtime depending on application settings. To do this, you also have an EmailFormatterManager class which is responsible for loading and validating formatters enabled in the application:

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// src/AppBundle/Mail/EmailFormatterManager.php
namespace AppBundle\Mail;

class EmailFormatterManager
{
    // ...

    public function getEnabledFormatters()
    {
        // code to configure which formatters to use
        $enabledFormatters = array(...);

        // ...

        return $enabledFormatters;
    }
}

If your goal is to avoid having to couple NewsletterManager and GreetingCardManager with EmailFormatterManager, then you might want to create a configurator class to configure these instances:

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// src/AppBundle/Mail/EmailConfigurator.php
namespace AppBundle\Mail;

class EmailConfigurator
{
    private $formatterManager;

    public function __construct(EmailFormatterManager $formatterManager)
    {
        $this->formatterManager = $formatterManager;
    }

    public function configure(EmailFormatterAwareInterface $emailManager)
    {
        $emailManager->setEnabledFormatters(
            $this->formatterManager->getEnabledFormatters()
        );
    }

    // ...
}

The EmailConfigurator's job is to inject the enabled formatters into NewsletterManager and GreetingCardManager because they are not aware of where the enabled formatters come from. On the other hand, the EmailFormatterManager holds the knowledge about the enabled formatters and how to load them, keeping the single responsibility principle.

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# app/config/services.yml
services:
    # ...

    # Registers all 4 classes as services, including AppBundle\Mail\EmailConfigurator
    AppBundle\:
        resource: '../../src/AppBundle/*'
        # ...

    # override the services to set the configurator
    AppBundle\Mail\NewsletterManager:
        configurator: 'AppBundle\Mail\EmailConfigurator:configure'

    AppBundle\Mail\GreetingCardManager:
        configurator: 'AppBundle\Mail\EmailConfigurator:configure'

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<!-- app/config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <prototype namespace="AppBundle\" resource="../../src/AppBundle/*" />

        <service id="AppBundle\Mail\NewsletterManager">
            <configurator service="AppBundle\Mail\EmailConfigurator" method="configure" />
        </service>

        <service id="AppBundle\Mail\GreetingCardManager">
            <configurator service="AppBundle\Mail\EmailConfigurator" method="configure" />
        </service>
    </services>
</container>

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// app/config/services.php
use AppBundle\Mail\GreetingCardManager;
use AppBundle\Mail\NewsletterManager;
use Symfony\Component\DependencyInjection\Definition;
use Symfony\Component\DependencyInjection\Reference;

// Same as before
$definition = new Definition();

$definition->setAutowired(true);

$this->registerClasses($definition, 'AppBundle\\', '../../src/AppBundle/*');

$container->getDefinition(NewsletterManager::class)
    ->setConfigurator(array(new Reference(EmailConfigurator::class), 'configure'));

$container->getDefinition(GreetingCardManager::class)
    ->setConfigurator(array(new Reference(EmailConfigurator::class), 'configure'));

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app.newsletter_manager:
    # new syntax
    configurator: 'AppBundle\Mail\EmailConfigurator:configure'
    # old syntax
    configurator: ['@AppBundle\Mail\EmailConfigurator', configure]