How to Inject Values Based on Complex Expressions
How to Inject Values Based on Complex Expressions¶
The service container also supports an “expression” that allows you to inject very specific values into a service.
For example, suppose you have a third service (not shown here), called mailer_configuration
,
which has a getMailerMethod()
method on it, which will return a string
like sendmail
based on some configuration. Remember that the first argument
to the my_mailer
service is the simple string sendmail
:
- YAML
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# app/config/services.yml services: app.mailer: class: AppBundle\Mailer arguments: [sendmail]
- XML
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<!-- app/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="app.mailer" class="AppBundle\Mailer"> <argument>sendmail</argument> </service> </services> </container>
- PHP
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// app/config/services.php use AppBundle\Mailer; $container->register('app.mailer', Mailer::class) ->addArgument('sendmail');
But instead of hardcoding this, how could we get this value from the getMailerMethod()
of the new mailer_configuration
service? One way is to use an expression:
- YAML
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# app/config/services.yml services: my_mailer: class: AppBundle\Mailer arguments: ["@=service('mailer_configuration').getMailerMethod()"]
- XML
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<!-- app/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="my_mailer" class="AppBundle\Mailer"> <argument type="expression">service('mailer_configuration').getMailerMethod()</argument> </service> </services> </container>
- PHP
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// app/config/services.php use AppBundle\Mailer; use Symfony\Component\ExpressionLanguage\Expression; $container->register('my_mailer', Mailer::class) ->addArgument(new Expression('service("mailer_configuration").getMailerMethod()'));
To learn more about the expression language syntax, see The Expression Syntax.
In this context, you have access to 2 functions:
service
- Returns a given service (see the example above).
parameter
- Returns a specific parameter value (syntax is just like
service
).
You also have access to the Symfony\Component\DependencyInjection\Container
via a container
variable. Here’s another example:
- YAML
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services: my_mailer: class: AppBundle\Mailer arguments: ["@=container.hasParameter('some_param') ? parameter('some_param') : 'default_value'"]
- XML
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<?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="my_mailer" class="AppBundle\Mailer"> <argument type="expression">container.hasParameter('some_param') ? parameter('some_param') : 'default_value'</argument> </service> </services> </container>
- PHP
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use AppBundle\Mailer; use Symfony\Component\ExpressionLanguage\Expression; $container->register('my_mailer', Mailer::class) ->addArgument(new Expression( "container.hasParameter('some_param') ? parameter('some_param') : 'default_value'" ));
Expressions can be used in arguments
, properties
, as arguments with
configurator
and as arguments to calls
(method calls).
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.