How to Inject Values Based on Complex Expressions
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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/services.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 Container
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).