Service Method Calls and Setter Injection

Tip

If you’re using autowiring, you can use @required to automatically configure method calls.

Usually, you’ll want to inject your dependencies via the constructor. But sometimes, especially if a dependency is optional, you may want to use “setter injection”. For example:

namespace App\Service;

use Psr\Log\LoggerInterface;

class MessageGenerator
{
    private $logger;

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

    // ...
}

To configure the container to call the setLogger method, use the calls key:

  • YAML
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    # config/services.yaml
services:
    App\Service\MessageGenerator:
        # ...
        calls:
            - [setLogger, ['@logger']]
  • XML
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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
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="App\Service\MessageGenerator">
            <!-- ... -->
            <call method="setLogger">
                <argument type="service" id="logger"/>
            </call>
        </service>
    </services>
</container>
  • PHP
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    // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use App\Service\MessageGenerator;

return function(ContainerConfigurator $configurator) {
    // ...

    $services->set(MessageGenerator::class)
        // In versions earlier to Symfony 5.1 the service() function was called ref()
        ->call('setLogger', [service('logger')]);
};

To provide immutable services, some classes implement immutable setters. Such setters return a new instance of the configured class instead of mutating the object they were called on:

namespace App\Service;

use Psr\Log\LoggerInterface;

class MessageGenerator
{
    private $logger;

    /**
     * @return static
     */
    public function withLogger(LoggerInterface $logger)
    {
        $new = clone $this;
        $new->logger = $logger;

        return $new;
    }

    // ...
}

Because the method returns a separate cloned instance, configuring such a service means using the return value of the wither method ($service = $service->withLogger($logger);). The configuration to tell the container it should do so would be like:

  • YAML
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    # config/services.yaml
services:
    App\Service\MessageGenerator:
        # ...
        calls:
            - withLogger: !returns_clone ['@logger']
  • XML
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    <!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="https://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\Service\MessageGenerator">
            <!-- ... -->
            <call method="withLogger" returns-clone="true">
                <argument type="service" id="logger"/>
            </call>
        </service>
    </services>
</container>
  • PHP
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    // config/services.php
use App\Service\MessageGenerator;
use Symfony\Component\DependencyInjection\Reference;

$container->register(MessageGenerator::class)
    ->addMethodCall('withLogger', [new Reference('logger')], true);