How to Decorate Services

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When overriding an existing definition, 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\NewMailer

Most of the time, that's exactly what you want to do. But sometimes, you might want to decorate the old one instead (i.e. apply the Decorator pattern). 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\DecoratingMailer.inner:

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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

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']

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']

The generated code will be the following:

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$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.
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