How to Decorate Services

Version: 4.2
Edit this page

Warning: You are browsing the documentation for Symfony 4.2, which is no longer maintained.

Read the updated version of this page for Symfony 5.3 (the current stable version).

How to Decorate Services

When overriding an existing definition, the original service is lost:

  • YAML
  • XML
  • PHP
1
2
3
4
5
6
7
8
# config/services.yaml
services:
    App\Mailer: ~

    # this replaces the old App\Mailer definition with the new one, the
    # old definition is lost
    App\Mailer:
        class: App\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:

  • YAML
  • XML
  • PHP
1
2
3
4
5
6
7
8
# config/services.yaml
services:
    App\Mailer: ~

    App\DecoratingMailer:
        # overrides the App\Mailer service
        # but that service is still available as App\DecoratingMailer.inner
        decorates: App\Mailer

The decorates option tells the container that the App\DecoratingMailer service replaces the App\Mailer service. If you're using the default services.yaml configuration, the decorated service is automatically injected when the constructor of the decorating service has one argument type-hinted with the decorated service class.

If you are not using autowiring or the decorating service has more than one constructor argument type-hinted with the decorated service class, you must inject the decorated service explicitly (the ID of the decorated service is automatically changed to decorating_service_id + '.inner'):

  • YAML
  • XML
  • PHP
1
2
3
4
5
6
7
8
# config/services.yaml
services:
    App\Mailer: ~

    App\DecoratingMailer:
        decorates: App\Mailer
        # pass the old service as an argument
        arguments: ['@App\DecoratingMailer.inner']

Tip

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\DecoratingMailer here), not of the decorated service (App\Mailer here). You can control the inner service name via the decoration_inner_name option:

  • YAML
  • XML
  • PHP
1
2
3
4
5
6
# config/services.yaml
services:
    App\DecoratingMailer:
        # ...
        decoration_inner_name: App\DecoratingMailer.wooz
        arguments: ['@App\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.

  • YAML
  • XML
  • PHP
1
2
3
4
5
6
7
8
9
10
11
12
13
14
# 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:

1
$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.