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.entity_manager service and an optional logger service:

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

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

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

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

    // ...
}

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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    services:
        app.base_doctrine_repository:
            # as no class is configured, the parent service MUST be abstract
            abstract:  true
            arguments: ['@doctrine.entity_manager']
            calls:
                - [setLogger, ['@logger']]
    
        app.user_repository:
            class:  AppBundle\Repository\DoctrineUserRepository
            # extend the app.base_doctrine_repository service
            parent: app.base_doctrine_repository
    
        app.post_repository:
            class:  AppBundle\Repository\DoctrinePostRepository
            parent: app.base_doctrine_repository
    
        # ...
    
  • XML
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    <?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>
            <!-- as no class is configured, the parent service MUST be abstract -->
            <service id="app.base_doctrine_repository" abstract="true">
                <argument type="service" id="doctrine.entity_manager">
    
                <call method="setLogger">
                    <argument type="service" id="logger" />
                </call>
            </service>
    
            <!-- extends the app.base_doctrine_repository service -->
            <service id="app.user_repository"
                class="AppBundle\Repository\DoctrineUserRepository"
                parent="app.base_doctrine_repository"
            />
    
            <service id="app.post_repository"
                class="AppBundle\Repository\DoctrineUserRepository"
                parent="app.base_doctrine_repository"
            />
    
            <!-- ... -->
        </services>
    </container>
    
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    use Symfony\Component\DependencyInjection\Reference;
    use Symfony\Component\DependencyInjection\DefinitionDecorator;
    
    // as no class is configured, the parent service MUST be abstract
    $container->register('app.base_doctrine_repository')
        ->addArgument(new Reference('doctrine.entity_manager'))
        ->addMethodCall('setLogger', array(new Reference('logger')))
    ;
    
    // extend the app.base_doctrine_repository service
    $definition = new DefinitionDecorator('app.base_doctrine_repository');
    $definition->setClass('AppBundle\Repository\DoctrineUserRepository');
    $container->setDefinition('app.user_repository', $definition);
    
    $definition = new DefinitionDecorator('app.base_doctrine_repository');
    $definition->setClass('AppBundle\Repository\DoctrinePostRepository');
    $container->setDefinition('app.post_repository', $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.user_repository is instantiated.

Caution

The shared, abstract and tags attributes are not inherited from parent services.

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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    services:
        # ...
    
        app.user_repository:
            class:  AppBundle\Repository\DoctrineUserRepository
            parent: app.base_doctrine_repository
    
            # 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.post_repository:
            class:  AppBundle\Repository\DoctrinePostRepository
            parent: app.base_doctrine_repository
    
            # overrides the first argument (using the special index_N key)
            arguments:
                index_0: '@doctrine.custom_entity_manager'
    
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    <?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.user_repository"
                class="AppBundle\Repository\DoctrineUserRepository"
                parent="app.base_doctrine_repository"
                public="false"
            >
                <!-- appends the '@app.username_checker' argument to the parent
                     argument list -->
                <argument type="service" id="app.username_checker" />
            </service>
    
            <service id="app.post_repository"
                class="AppBundle\Repository\DoctrineUserRepository"
                parent="app.base_doctrine_repository"
            >
                <!-- 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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    use Symfony\Component\DependencyInjection\Reference;
    use Symfony\Component\DependencyInjection\DefinitionDecorator;
    // ...
    
    $definition = new DefinitionDecorator('app.base_doctrine_repository');
    $definition->setClass('AppBundle\Repository\DoctrineUserRepository');
    // 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('app.user_repository', $definition);
    
    $definition = new DefinitionDecorator('app.base_doctrine_repository');
    $definition->setClass('AppBundle\Repository\DoctrinePostRepository');
    // overrides the first argument
    $definition->replaceArgument(0, new Reference('doctrine.custom_entity_manager'));
    $container->setDefinition('app.post_repository', $definition);
    

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