Symfony 4 was released on November 30th.
Update now to the best Symfony ever!

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:

  • YAML
    1
    2
    3
    4
    5
    6
    7
    8
    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
    
  • XML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    <?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>
    
  • PHP
    1
    2
    3
    4
    5
    6
    7
    8
    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 service instead and keep the old service so that you can reference it:

  • YAML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    services:
        app.mailer:
            class: AppBundle\Mailer
    
        app.decorating_mailer:
            class:     AppBundle\DecoratingMailer
            # overrides the app.mailer service
            # but that service is still available as app.decorating_mailer.inner
            decorates: app.mailer
    
            # pass the old service as an argument
            arguments: ['@app.decorating_mailer.inner']
    
            # private, because usually you do not need to fetch app.decorating_mailer directly
            public:    false
    
  • XML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    <?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" />
    
            <service id="app.decorating_mailer"
                class="AppBundle\DecoratingMailer"
                decorates="app.mailer"
                public="false"
            >
                <argument type="service" id="app.decorating_mailer.inner" />
            </service>
    
        </services>
    </container>
    
  • PHP
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    use AppBundle\DecoratingMailer;
    use AppBundle\Mailer;
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register('app.mailer', Mailer::class);
    
    $container->register('app.decorating_mailer', DecoratingMailer::class)
        ->setDecoratedService('app.mailer')
        ->addArgument(new Reference('app.decorating_mailer.inner'))
        ->setPublic(false)
    ;
    

The decorates option tells the container that the app.decorating_mailer service replaces the app.mailer service. The old app.mailer service is renamed to app.decorating_mailer.inner so you can inject it into your new service.

Tip

The visibility (public) 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). You can control the inner service name via the decoration_inner_name option:

  • YAML
    1
    2
    3
    4
    5
    services:
        app.decorating_mailer:
            # ...
            decoration_inner_name: app.decorating_mailer.wooz
            arguments: ['@app.decorating_mailer.wooz']
    
  • XML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    <?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>
    
  • PHP
    1
    2
    3
    4
    5
    6
    7
    8
    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'))
        // ...
    ;
    

Decoration Priority

If you want to apply more than one decorator to a service, you can control their order by configuring the priority of decoration, this can be any integer number (decorators with higher priorities will be applied first).

  • YAML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    foo:
        class: Foo
    
    bar:
        class: Bar
        public: false
        decorates: foo
        decoration_priority: 5
        arguments: ['@bar.inner']
    
    baz:
        class: Baz
        public: false
        decorates: foo
        decoration_priority: 1
        arguments: ['@baz.inner']
    
  • XML
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    <?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" class="Foo" />
    
            <service id="bar" class="Bar" decorates="foo" decoration-priority="5" public="false">
                <argument type="service" id="bar.inner" />
            </service>
    
            <service id="baz" class="Baz" decorates="foo" decoration-priority="1" public="false">
                <argument type="service" id="baz.inner" />
            </service>
        </services>
    </container>
    
  • PHP
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    use Symfony\Component\DependencyInjection\Reference;
    
    $container->register('foo', 'Foo')
    
    $container->register('bar', 'Bar')
        ->addArgument(new Reference('bar.inner'))
        ->setPublic(false)
        ->setDecoratedService('foo', null, 5);
    
    $container->register('baz', 'Baz')
        ->addArgument(new Reference('baz.inner'))
        ->setPublic(false)
        ->setDecoratedService('foo', null, 1);
    

The generated code will be the following:

$this->services['foo'] = new Baz(new Bar(new Foo()));

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