How to Inject Values Based on Complex Expressions

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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:

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# app/config/services.yml
services:
    app.mailer:
        class:        AppBundle\Mailer
        arguments:    [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:

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# app/config/config.yml
services:
    my_mailer:
        class:     AppBundle\Mailer
        arguments: ["@=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 ContainerBuilder via a container variable. Here's another example:

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services:
    my_mailer:
        class:     AppBundle\Mailer
        arguments: ["@=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.