Warning: You are browsing the documentation for Symfony 3.4, which is no longer maintained.

Read the updated version of this page for Symfony 5.3 (the current stable version).

How to Inject Values Based on Complex Expressions

3.4 version

Maintained

4.4 5.3 current 5.4 dev 6.0

Unmaintained

2.7 2.8 3.0 3.1 3.2 3.3 3.4 4.0 4.1 4.2 4.3 5.0 5.1 5.2

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 AppBundle\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: AppBundle\Mailer. One way to do this is with an expression:

YAML

# app/config/services.yml
services:
    # ...

    AppBundle\Mail\MailerConfiguration: ~

    AppBundle\Mailer:
        # the '@=' prefix is required when using expressions for arguments in YAML files
        arguments: ["@=service('AppBundle\\\\Mail\\\\MailerConfiguration').getMailerMethod()"]

XML

<!-- 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
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <!-- ... -->

        <service id="AppBundle\Mail\MailerConfiguration"></service>

        <service id="AppBundle\Mailer">
            <argument type="expression">service('App\\Mail\\MailerConfiguration').getMailerMethod()</argument>
        </service>
    </services>
</container>

PHP

// app/config/services.php
use AppBundle\Mail\MailerConfiguration;
use AppBundle\Mailer;
use Symfony\Component\ExpressionLanguage\Expression;

$container->autowire(MailerConfiguration::class);

$container->autowire(Mailer::class)
    ->addArgument(new Expression('service("AppBundle\\\\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 just like service).

You also have access to the Symfony\Component\DependencyInjection\Container via a container variable. Here’s another example:

YAML

services:
    AppBundle\Mailer:
        # the '@=' prefix is required when using expressions for arguments in YAML files
        arguments: ["@=container.hasParameter('some_param') ? parameter('some_param') : 'default_value'"]

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="AppBundle\Mailer">
            <argument type="expression">container.hasParameter('some_param') ? parameter('some_param') : 'default_value'</argument>
        </service>
    </services>
</container>

PHP

use AppBundle\Mailer;
use Symfony\Component\ExpressionLanguage\Expression;

$container->autowire(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.