How to Manage Common Dependencies with Parent Services

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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;

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): void
    {
        $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
{
    // ...
}

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

    # ...

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:

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