How to Manage Common Dependencies with Parent Services

As you add more functionality to your application, you may well start to have related classes that share some of the same dependencies. For example, you may have multiple repository classes which need the doctrine.orm.entity_manager service and an optional logger service:

// src/Repository/BaseDoctrineRepository.php
namespace App\Repository;

use Doctrine\Persistence\ObjectManager;
use Psr\Log\LoggerInterface;

// ...
abstract class BaseDoctrineRepository
{
    protected $objectManager;
    protected $logger;

    public function __construct(ObjectManager $objectManager)
    {
        $this->objectManager = $objectManager;
    }

    public function setLogger(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    // ...
}

Your child service classes may look like this:

// src/Repository/DoctrineUserRepository.php
namespace App\Repository;

use App\Repository\BaseDoctrineRepository;

// ...
class DoctrineUserRepository extends BaseDoctrineRepository
{
    // ...
}

// src/Repository/DoctrinePostRepository.php
namespace App\Repository;

use App\Repository\BaseDoctrineRepository;

// ...
class DoctrinePostRepository extends BaseDoctrineRepository
{
    // ...
}

Just as you use PHP inheritance to avoid duplication in your PHP code, the service container allows you to extend parent services in order to avoid duplicated service definitions:

• YAML

  # config/services.yaml
  services:
      App\Repository\BaseDoctrineRepository:
          abstract:  true
          arguments: ['@doctrine.orm.entity_manager']
          calls:
              - [setLogger, ['@logger']]
  
      App\Repository\DoctrineUserRepository:
          # extend the App\Repository\BaseDoctrineRepository service
          parent: App\Repository\BaseDoctrineRepository
  
      App\Repository\DoctrinePostRepository:
          parent: App\Repository\BaseDoctrineRepository
  
      # ...
  

• XML

  <!-- 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
          https://symfony.com/schema/dic/services/services-1.0.xsd">
  
      <services>
          <service id="App\Repository\BaseDoctrineRepository" abstract="true">
              <argument type="service" id="doctrine.orm.entity_manager"/>
  
              <call method="setLogger">
                  <argument type="service" id="logger"/>
              </call>
          </service>
  
          <!-- extends the App\Repository\BaseDoctrineRepository service -->
          <service id="App\Repository\DoctrineUserRepository"
              parent="App\Repository\BaseDoctrineRepository"
          />
  
          <service id="App\Repository\DoctrinePostRepository"
              parent="App\Repository\BaseDoctrineRepository"
          />
  
          <!-- ... -->
      </services>
  </container>
  

• PHP

  // config/services.php
  namespace Symfony\Component\DependencyInjection\Loader\Configurator;
  
  use App\Repository\BaseDoctrineRepository;
  use App\Repository\DoctrinePostRepository;
  use App\Repository\DoctrineUserRepository;
  
  return function(ContainerConfigurator $configurator) {
      $services = $configurator->services();
  
      $services->set(BaseDoctrineRepository::class)
          ->abstract()
          ->args([service('doctrine.orm.entity_manager')])
          // In versions earlier to Symfony 5.1 the service() function was called ref()
          ->call('setLogger', [service('logger')])
      ;
  
      $services->set(DoctrineUserRepository::class)
          // extend the App\Repository\BaseDoctrineRepository service
          ->parent(BaseDoctrineRepository::class)
      ;
  
      $services->set(DoctrinePostRepository::class)
          ->parent(BaseDoctrineRepository::class)
      ;
  };
  

In this context, having a parent service implies that the arguments and method calls of the parent service should be used for the child services. Specifically, the EntityManager will be injected and setLogger() will be called when App\Repository\DoctrineUserRepository is instantiated.

All attributes on the parent service are shared with the child except for shared, abstract and tags. These are not inherited from the parent.

Tip

In the examples shown, the classes sharing the same configuration also extend from the same parent class in PHP. This isn’t necessary at all. You can also extract common parts of similar service definitions into a parent service without also extending a parent class in PHP.

Overriding Parent Dependencies

There may be times where you want to override what service is injected for one child service only. You can override most settings by specifying it in the child class:

• YAML

  # config/services.yaml
  services:
      # ...
  
      App\Repository\DoctrineUserRepository:
          parent: App\Repository\BaseDoctrineRepository
  
          # overrides the private setting of the parent service
          public: true
  
          # appends the '@app.username_checker' argument to the parent
          # argument list
          arguments: ['@app.username_checker']
  
      App\Repository\DoctrinePostRepository:
          parent: App\Repository\BaseDoctrineRepository
  
          # overrides the first argument (using the special index_N key)
          arguments:
              index_0: '@doctrine.custom_entity_manager'
  

• XML

  <!-- 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
          https://symfony.com/schema/dic/services/services-1.0.xsd">
  
      <services>
          <!-- ... -->
  
          <!-- overrides the private setting of the parent service -->
          <service id="App\Repository\DoctrineUserRepository"
              parent="App\Repository\BaseDoctrineRepository"
              public="true"
          >
              <!-- appends the '@app.username_checker' argument to the parent
                   argument list -->
              <argument type="service" id="app.username_checker"/>
          </service>
  
          <service id="App\Repository\DoctrinePostRepository"
              parent="App\Repository\BaseDoctrineRepository"
          >
              <!-- overrides the first argument (using the index attribute) -->
              <argument index="0" type="service" id="doctrine.custom_entity_manager"/>
          </service>
  
          <!-- ... -->
      </services>
  </container>
  

• PHP

  // config/services.php
  namespace Symfony\Component\DependencyInjection\Loader\Configurator;
  
  use App\Repository\BaseDoctrineRepository;
  use App\Repository\DoctrinePostRepository;
  use App\Repository\DoctrineUserRepository;
  // ...
  
  return function(ContainerConfigurator $configurator) {
      $services = $configurator->services();
  
      $services->set(BaseDoctrineRepository::class)
          // ...
      ;
  
      $services->set(DoctrineUserRepository::class)
          ->parent(BaseDoctrineRepository::class)
  
          // overrides the private setting of the parent service
          ->public()
  
          // appends the '@app.username_checker' argument to the parent
          // argument list
          ->args([service('app.username_checker')])
      ;
  
      $services->set(DoctrinePostRepository::class)
          ->parent(BaseDoctrineRepository::class)
  
          # overrides the first argument
          ->arg(0, service('doctrine.custom_entity_manager'))
      ;
  };