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How to Decorate Services

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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    # config/services.yaml
    services:
        AppBundle\Mailer: ~
    
        # this replaces the old AppBundle\Mailer definition with the new one, the
        # old definition is lost
        AppBundle\Mailer:
            class: AppBundle\DecoratingMailer
    
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    <!-- config/services.xml -->
    <?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="AppBundle\Mailer" />
    
            <!-- this replaces the old AppBundle\Mailer definition with the new
                 one, the old definition is lost -->
            <service id="AppBundle\Mailer" class="AppBundle\DecoratingMailer" />
        </services>
    </container>
    
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    // config/services.php
    use AppBundle\Mailer;
    use AppBundle\DecoratingMailer;
    
    $container->register(Mailer::class);
    
    // this replaces the old AppBundle\Mailer definition with the new one, the
    // old definition is lost
    $container->register(Mailer::class, DecoratingMailer::class);
    

Most of the time, that's exactly what you want to do. But sometimes, you might want to decorate the old service instead and keep the old service so that you can reference it:

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    # config/services.yaml
    services:
        AppBundle\Mailer: ~
    
        AppBundle\DecoratingMailer:
            # overrides the AppBundle\Mailer service
            # but that service is still available as AppBundle\DecoratingMailer.inner
            decorates: AppBundle\Mailer
    
            # pass the old service as an argument
            arguments: ['@AppBundle\DecoratingMailer.inner']
    
            # private, because usually you do not need to fetch AppBundle\DecoratingMailer directly
            public:    false
    
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    <!-- config/services.xml -->
    <?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="AppBundle\Mailer" />
    
            <service id="AppBundle\DecoratingMailer"
                decorates="AppBundle\Mailer"
                public="false"
            >
                <argument type="service" id="AppBundle\DecoratingMailer.inner" />
            </service>
    
        </services>
    </container>
    
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    // config/services.php
    use AppBundle\DecoratingMailer;
    use AppBundle\Mailer;
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register(Mailer::class);
    
    $container->register(DecoratingMailer::class)
        ->setDecoratedService(Mailer::class)
        ->addArgument(new Reference(DecoratingMailer::class.'.inner'))
        ->setPublic(false)
    ;
    

The decorates option tells the container that the AppBundle\DecoratingMailer service replaces the AppBundle\Mailer service. The old AppBundle\Mailer service is renamed to AppBundle\DecoratingMailer.inner so you can inject it into your new service.

Tip

The visibility (public) of the decorated AppBundle\Mailer service (which is an alias for the new service) will still be the same as the original AppBundle\Mailer visibility.

Note

The generated inner id is based on the id of the decorator service (AppBundle\DecoratingMailer here), not of the decorated service (AppBundle\Mailer here). You can control the inner service name via the decoration_inner_name option:

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    # config/services.yaml
    services:
        AppBundle\DecoratingMailer:
            # ...
            decoration_inner_name: AppBundle\DecoratingMailer.wooz
            arguments: ['@AppBundle\DecoratingMailer.wooz']
    
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    <!-- config/services.xml -->
    <?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="AppBundle\DecoratingMailer"
                decorates="AppBundle\Mailer"
                decoration-inner-name="AppBundle\DecoratingMailer.wooz"
                public="false"
            >
                <argument type="service" id="AppBundle\DecoratingMailer.wooz" />
            </service>
    
        </services>
    </container>
    
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    // config/services.php
    use AppBundle\DecoratingMailer;
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register(DecoratingMailer::class)
        ->setDecoratedService(AppBundle\Mailer, DecoratingMailer::class.'.wooz')
        ->addArgument(new Reference(DecoratingMailer::class.'.wooz'))
        // ...
    ;
    

Decoration Priority

When applying multiple decorators to a service, you can control their order with the decoration_priority option. Its value is an integer that defaults to 0 and higher priorities mean that decorators will be applied earlier.

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    # config/services.yaml
    Foo: ~
    
    Bar:
        public: false
        decorates: Foo
        decoration_priority: 5
        arguments: ['@Bar.inner']
    
    Baz:
        public: false
        decorates: Foo
        decoration_priority: 1
        arguments: ['@Baz.inner']
    
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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="Foo" />
    
            <service id="Bar" decorates="Foo" decoration-priority="5" public="false">
                <argument type="service" id="Bar.inner" />
            </service>
    
            <service id="Baz" decorates="Foo" decoration-priority="1" public="false">
                <argument type="service" id="Baz.inner" />
            </service>
        </services>
    </container>
    
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    // config/services.php
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register(Foo:class)
    
    $container->register(Bar:class)
        ->addArgument(new Reference(Bar:class.'inner'))
        ->setPublic(false)
        ->setDecoratedService(Foo:class, null, 5);
    
    $container->register(Baz:class)
        ->addArgument(new Reference(Baz:class.'inner'))
        ->setPublic(false)
        ->setDecoratedService(Foo:class, null, 1);
    

The generated code will be the following:

$this->services[Foo:class] = new Baz(new Bar(new Foo()));

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