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How to Manage Common Dependencies with 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:

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

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

    public function __construct(EntityManagerInterface $manager)
    {
        $this->entityManager = $manager;
    }

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

    // ...
}

Your child service classes may look like this:

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// 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:

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    # 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
    
        # ...
    
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    <!-- 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>
            <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>
    
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    // config/services.php
    use App\Repository\DoctrineUserRepository;
    use App\Repository\DoctrinePostRepository;
    use App\Repository\BaseDoctrineRepository;
    use Symfony\Component\DependencyInjection\ChildDefinition;
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register(BaseDoctrineRepository::class)
        ->setAbstract(true)
        ->addArgument(new Reference('doctrine.orm.entity_manager'))
        ->addMethodCall('setLogger', array(new Reference('logger')))
    ;
    
    // extend the App\Repository\BaseDoctrineRepository service
    $definition = new ChildDefinition(BaseDoctrineRepository::class);
    $definition->setClass(DoctrineUserRepository::class);
    $container->setDefinition(DoctrineUserRepository::class, $definition);
    
    $definition = new ChildDefinition(BaseDoctrineRepository::class);
    $definition->setClass(DoctrinePostRepository::class);
    $container->setDefinition(DoctrinePostRepository::class, $definition);
    
    // ...
    

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.

Note

If you have a _defaults section in your file, all child services are required to explicitly override those values to avoid ambiguity. You will see a clear error message about this.

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 just 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 simply specifying it in the child class:

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    # config/services.yaml
    services:
        # ...
    
        App\Repository\DoctrineUserRepository:
            parent: App\Repository\BaseDoctrineRepository
    
            # overrides the public setting of the parent service
            public: false
    
            # 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'
    
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    <!-- 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>
            <!-- ... -->
    
            <!-- overrides the public setting of the parent service -->
            <service id="App\Repository\DoctrineUserRepository"
                parent="App\Repository\BaseDoctrineRepository"
                public="false"
            >
                <!-- 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>
    
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    // config/services.php
    use App\Repository\DoctrineUserRepository;
    use App\Repository\DoctrinePostRepository;
    use App\Repository\BaseDoctrineRepository;
    use Symfony\Component\DependencyInjection\ChildDefinition;
    use Symfony\Component\DependencyInjection\Reference;
    // ...
    
    $definition = new ChildDefinition(BaseDoctrineRepository::class);
    $definition->setClass(DoctrineUserRepository::class);
    // overrides the public setting of the parent service
    $definition->setPublic(false);
    // appends the '@app.username_checker' argument to the parent argument list
    $definition->addArgument(new Reference('app.username_checker'));
    $container->setDefinition(DoctrineUserRepository::class, $definition);
    
    $definition = new ChildDefinition(BaseDoctrineRepository::class);
    $definition->setClass(DoctrinePostRepository::class);
    // overrides the first argument
    $definition->replaceArgument(0, new Reference('doctrine.custom_entity_manager'));
    $container->setDefinition(DoctrinePostRepository::class, $definition);
    

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.