Configuring Services with a Service Configurator

The Service Configurator is a feature of the Dependency Injection Container that allows you to use a callable to configure a service after its instantiation.

You can specify a method in another service, a PHP function or a static method in a class. The service instance is passed to the callable, allowing the configurator to do whatever it needs to configure the service after its creation.

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 interesting 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:

class NewsletterManager implements EmailFormatterAwareInterface
{
    protected $mailer;
    protected $enabledFormatters;

    public function setMailer(Mailer $mailer)
    {
        $this->mailer = $mailer;
    }

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

    // ...
}

and also a GreetingCardManager class:

class GreetingCardManager implements EmailFormatterAwareInterface
{
    protected $mailer;
    protected $enabledFormatters;

    public function setMailer(Mailer $mailer)
    {
        $this->mailer = $mailer;
    }

    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:

class EmailFormatterManager
{
    protected $enabledFormatters;

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

        $this->enabledFormatters = $enabledFormatters;
    }

    public function getEnabledFormatters()
    {
        return $this->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:

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 filters into NewsletterManager and GreetingCardManager because they are not aware of where the enabled filters come from. In the other hand, the EmailFormatterManager holds the knowledge about the enabled formatters and how to load them, keeping the single responsibility principle.

Configurator Service Config

The service config for the above classes would look something like this:

• YAML

  services:
      my_mailer:
          # ...
  
      email_formatter_manager:
          class:     EmailFormatterManager
          # ...
  
      email_configurator:
          class:     EmailConfigurator
          arguments: ["@email_formatter_manager"]
          # ...
  
      newsletter_manager:
          class:     NewsletterManager
          calls:
              - [setMailer, ["@my_mailer"]]
          configurator: ["@email_configurator", configure]
  
      greeting_card_manager:
          class:     GreetingCardManager
          calls:
              - [setMailer, ["@my_mailer"]]
          configurator: ["@email_configurator", configure]
  

• 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>
          <service id="my_mailer">
              <!-- ... -->
          </service>
  
          <service id="email_formatter_manager" class="EmailFormatterManager">
              <!-- ... -->
          </service>
  
          <service id="email_configurator" class="EmailConfigurator">
              <argument type="service" id="email_formatter_manager" />
              <!-- ... -->
          </service>
  
          <service id="newsletter_manager" class="NewsletterManager">
              <call method="setMailer">
                  <argument type="service" id="my_mailer" />
              </call>
              <configurator service="email_configurator" method="configure" />
          </service>
  
          <service id="greeting_card_manager" class="GreetingCardManager">
              <call method="setMailer">
                  <argument type="service" id="my_mailer" />
              </call>
              <configurator service="email_configurator" method="configure" />
          </service>
      </services>
  </container>
  

• PHP

  use Symfony\Component\DependencyInjection\Definition;
  use Symfony\Component\DependencyInjection\Reference;
  
  // ...
  $container->setDefinition('my_mailer', ...);
  $container->setDefinition('email_formatter_manager', new Definition(
      'EmailFormatterManager'
  ));
  $container->setDefinition('email_configurator', new Definition(
      'EmailConfigurator'
  ));
  $container->setDefinition('newsletter_manager', new Definition(
      'NewsletterManager'
  ))->addMethodCall('setMailer', array(
      new Reference('my_mailer'),
  ))->setConfigurator(array(
      new Reference('email_configurator'),
      'configure',
  )));
  $container->setDefinition('greeting_card_manager', new Definition(
      'GreetingCardManager'
  ))->addMethodCall('setMailer', array(
      new Reference('my_mailer'),
  ))->setConfigurator(array(
      new Reference('email_configurator'),
      'configure',
  )));