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 service (not shown here), called App\Mail\MailerConfiguration
,
which has a getMailerMethod()
method on it. This returns a string - like sendmail
based on some configuration.
Suppose that you want to pass the result of this method as a constructor argument
to another service: App\Mailer
. One way to do this is with an expression:
- YAML
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# config/services.yaml services: # ... App\Mail\MailerConfiguration: ~ App\Mailer: # the '@=' prefix is required when using expressions for arguments in YAML files arguments: ['@=service("App\\Mail\\MailerConfiguration").getMailerMethod()'] # when using double-quoted strings, the backslash needs to be escaped twice (see https://yaml.org/spec/1.2/spec.html#id2787109) # arguments: ["@=service('App\\\\Mail\\\\MailerConfiguration').getMailerMethod()"]
- XML
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<!-- 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 https://symfony.com/schema/dic/services/services-1.0.xsd"> <services> <!-- ... --> <service id="App\Mail\MailerConfiguration"></service> <service id="App\Mailer"> <argument type="expression">service('App\\Mail\\MailerConfiguration').getMailerMethod()</argument> </service> </services> </container>
- PHP
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// config/services.php namespace Symfony\Component\DependencyInjection\Loader\Configurator; use App\Mail\MailerConfiguration; use App\Mailer; return function(ContainerConfigurator $configurator) { // ... $services->set(MailerConfiguration::class); $services->set(Mailer::class) ->args([expr("service('App\\Mail\\MailerConfiguration').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 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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# config/services.yaml services: App\Mailer: # the '@=' prefix is required when using expressions for arguments in YAML files arguments: ["@=container.hasParameter('some_param') ? parameter('some_param') : 'default_value'"]
- XML
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<!-- 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 https://symfony.com/schema/dic/services/services-1.0.xsd"> <services> <service id="App\Mailer"> <argument type="expression">container.hasParameter('some_param') ? parameter('some_param') : 'default_value'</argument> </service> </services> </container>
- PHP
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// config/services.php namespace Symfony\Component\DependencyInjection\Loader\Configurator; use App\Mailer; return function(ContainerConfigurator $configurator) { $services = $configurator->services(); $services->set(Mailer::class) ->args([expr("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.