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()));