.. index:: single: DependencyInjection; Parent services 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: .. configuration-block:: .. code-block:: 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 # ... .. code-block:: xml .. code-block:: 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([ref('doctrine.orm.entity_manager')]) ->call('setLogger', [ref('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: .. configuration-block:: .. code-block:: 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' .. code-block:: xml .. code-block:: 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([ref('app.username_checker')]) ; $services->set(DoctrinePostRepository::class) ->parent(BaseDoctrineRepository::class) # overrides the first argument ->arg(0, ref('doctrine.custom_entity_manager')) ; };