Importing Configuration with imports

So far, you've placed your app.mailer service container definition directly in the services configuration file (e.g. app/config/services.yml). If your application ends up having many services, this file becomes huge and hard to maintain. To avoid this, you can split your service configuration into multiple service files:

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# app/config/services/mailer.yml
parameters:
    app.mailer.transport: sendmail

services:
    app.mailer:
        class:     AppBundle\Mailer
        arguments: ['%app.mailer.transport%']

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<!-- app/config/services/mailer.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">

    <parameters>
        <parameter key="app.mailer.transport">sendmail</parameter>
    </parameters>

    <services>
        <service id="app.mailer" class="AppBundle\Mailer">
            <argument>%app.mailer.transport%</argument>
        </service>
    </services>
</container>

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// app/config/services/mailer.php
use AppBundle\Mailer;

$container->setParameter('app.mailer.transport', 'sendmail');

$container->register('app.mailer', Mailer::class)
    ->addArgument('%app.mailer.transport%');

The definition itself hasn't changed, only its location. To make the service container load the definitions in this resource file, use the imports key in any already loaded resource (e.g. app/config/services.yml or app/config/config.yml):

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# app/config/services.yml
imports:
    - { resource: services/mailer.yml }

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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">

    <imports>
        <import resource="services/mailer.xml"/>
    </imports>
</container>

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// app/config/services.php
$loader->import('services/mailer.php');

The resource location, for files, is either a relative path from the current file or an absolute path.

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# app/config/config.yml
imports:
    - { resource: '%kernel.root_dir%/parameters.yml' }

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<!-- app/config/config.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">

    <imports>
        <import resource="%kernel.root_dir%/parameters.yml" />
    </imports>
</container>

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// app/config/config.php
$loader->import('%kernel.root_dir%/parameters.yml');

Importing Configuration via Container Extensions

Third-party bundle container configuration, including Symfony core services, are usually loaded using another method that's more flexible and easy to configure in your application.

Internally, each bundle defines its services like you've seen so far. However, these files aren't imported using the import directive. These bundles use a dependency injection extension to load the files. The extension also allows bundles to provide configuration to dynamically load some services.

Take the FrameworkBundle - the core Symfony Framework bundle - as an example. The presence of the following code in your application configuration invokes the service container extension inside the FrameworkBundle:

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# app/config/config.yml
framework:
    secret: xxxxxxxxxx
    form:   true
    # ...

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<!-- app/config/config.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony http://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config secret="xxxxxxxxxx">
        <framework:form />

        <!-- ... -->
    </framework:config>
</container>

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// app/config/config.php
$container->loadFromExtension('framework', array(
    'secret' => 'xxxxxxxxxx',
    'form'   => array(),
    // ...
));

When the resources are parsed, the container looks for an extension that can handle the framework directive. The extension in question, which lives in the FrameworkBundle, is invoked and the service configuration for the FrameworkBundle is loaded.

The settings under the framework directive (e.g. form: true) indicate that the extension should load all services related to the Form component. If form was disabled, these services wouldn't be loaded and Form integration would not be available.

When installing or configuring a bundle, see the bundle's documentation for how the services for the bundle should be installed and configured. The options available for the core bundles can be found inside the Reference Guide.