How to Decorate Services

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How to Decorate Services

When overriding an existing definition (e.g. when applying the Decorator pattern), the original service is lost:

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        services:
    app.mailer:
        class: AppBundle\Mailer

    # this replaces the old app.mailer definition with the new one, the
    # old definition is lost
    app.mailer:
        class: AppBundle\DecoratingMailer
    

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        <?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"
    xsd:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="app.mailer" class="AppBundle\Mailer" />

        <!-- this replaces the old app.mailer definition with the new
             one, the old definition is lost -->
        <service id="app.mailer" class="AppBundle\DecoratingMailer" />
    </services>
</container>
    

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        use AppBundle\Mailer;
use AppBundle\DecoratingMailer;

$container->register('app.mailer', Mailer::class);

// this replaces the old app.mailer definition with the new one, the
// old definition is lost
$container->register('app.mailer', DecoratingMailer::class);
    

Most of the time, that's exactly what you want to do. But sometimes, you might want to decorate the old one instead. In this case, the old service should be kept around to be able to reference it in the new one. This configuration replaces app.mailer with a new one, but keeps a reference of the old one as app.decorating_mailer.inner:

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        services:
    # ...

    app.decorating_mailer:
        class:     AppBundle\DecoratingMailer
        decorates: app.mailer
        arguments: ['@app.decorating_mailer.inner']
        public:    false
    

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        <?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"
    xsd:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <!-- ... -->

        <service id="app.decorating_mailer"
            class="AppBundle\DecoratingMailer"
            decorates="app.mailer"
            public="false"
        >
            <argument type="service" id="app.decorating_mailer.inner" />
        </service>

    </services>
</container>
    

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        use AppBundle\DecoratingMailer;
use Symfony\Component\DependencyInjection\Reference;

// ...
$container->register('app.decorating_mailer', DecoratingMailer::class)
    ->setDecoratedService('app.mailer')
    ->addArgument(new Reference('app.decorating_mailer.inner'))
    ->setPublic(false)
;
    

Here is what's going on here: the decorates option tells the container that the app.decorating_mailer service replaces the app.mailer service. By convention, the old app.mailer service is renamed to app.decorating_mailer.inner, so you can inject it into your new service.

Tip

Most of the time, the decorator should be declared private, as you will not need to retrieve it as app.decorating_mailer from the container.

The visibility of the decorated app.mailer service (which is an alias for the new service) will still be the same as the original app.mailer visibility.

Note

The generated inner id is based on the id of the decorator service (app.decorating_mailer here), not of the decorated service (app.mailer here). This is mandatory to allow several decorators on the same service (they need to have different generated inner ids).

You can change the inner service name if you want to using the decoration_inner_name option:

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        services:
    app.decorating_mailer:
        # ...
        decoration_inner_name: app.decorating_mailer.wooz
        arguments: ['@app.decorating_mailer.wooz']
    

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        <?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"
    xsd:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <!-- ... -->

        <service
            id="app.decorating_mailer"
            class="AppBundle\DecoratingMailer"
            decorates="app.mailer"
            decoration-inner-name="app.decorating_mailer.wooz"
            public="false"
        >
            <argument type="service" id="app.decorating_mailer.wooz" />
        </service>

    </services>
</container>
    

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        use AppBundle\DecoratingMailer;
use Symfony\Component\DependencyInjection\Reference;

$container->register('app.decorating_mailer', DecoratingMailer::class)
    ->setDecoratedService('app.mailer', 'app.decorating_mailer.wooz')
    ->addArgument(new Reference('app.decorating_mailer.wooz'))
    // ...
;
    

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

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