Importing Configuration with imports

By default, service configuration lives in config/services.yaml. But if that file becomes large, you're free to organize into multiple files. Suppose you decided to move some configuration to a new file:

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# config/services/mailer.yaml
parameters:
    # ... some parameters

services:
    # ... some services

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

    <parameters>
        <!-- ... some parameters -->
    </parameters>

    <services>
        <!-- ... some services -->
    </services>
</container>

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// config/services/mailer.php

// ... some parameters
// ... some services

To import this file, use the imports key from any other file and pass either a relative or absolute path to the imported file:

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# config/services.yaml
imports:
    - { resource: services/mailer.yaml }
    # If you want to import a whole directory:
    - { resource: services/ }
services:
    _defaults:
        autowire: true
        autoconfigure: true

    App\:
        resource: '../src/*'
        exclude: '../src/{DependencyInjection,Entity,Migrations,Tests,Kernel.php}'

    # ...

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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">

    <imports>
        <import resource="services/mailer.xml"/>
        <!-- If you want to import a whole directory: -->
        <import resource="services/"/>
    </imports>

    <services>
        <defaults autowire="true" autoconfigure="true"/>

        <prototype namespace="App\" resource="../src/*"
            exclude="../src/{DependencyInjection,Entity,Migrations,Tests,Kernel.php}"/>

        <!-- ... -->
    </services>
</container>

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// config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

return function(ContainerConfigurator $container) {
    $container->import('services/mailer.php');
    // If you want to import a whole directory:
    $container->import('services/');

    $services = $container->services()
        ->defaults()
            ->autowire()
            ->autoconfigure()
    ;

    $services->load('App\\', '../src/*')
        ->exclude('../src/{DependencyInjection,Entity,Migrations,Tests,Kernel.php}');
};

When loading a configuration file, Symfony loads first the imported files and then it processes the parameters and services defined in the file. If you use the default services.yaml configuration as in the above example, the App\ definition creates services for classes found in ../src/*. If your imported file defines services for those classes too, they will be overridden.

A possible solution for this is to add the classes and/or directories of the imported files in the exclude option of the App\ definition. Another solution is to not use imports and add the service definitions in the same file, but after the App\ definition to override it.

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# config/services.yaml
imports:
    - { resource: '%kernel.project_dir%/somefile.yaml' }

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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"
>
    <imports>
        <import resource="%kernel.project_dir%/somefile.yaml"/>
    </imports>
</container>

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// config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

return static function (ContainerConfigurator $container) {
    $container->import('%kernel.project_dir%/somefile.yaml');
};

Importing Configuration via Container Extensions

Third-party bundle container configuration, including Symfony core services, are usually loaded using another method: a container extension.

Internally, each bundle defines its services in files like you've seen so far. However, these files aren't imported using the import directive. Instead, bundles use a dependency injection extension to load the files automatically. As soon as you enable a bundle, its extension is called, which is able to load service configuration files.

In fact, each configuration file in config/packages/ is passed to the extension of its related bundle - e.g. FrameworkBundle or TwigBundle - and used to configure those services further.