class BackendCompilerPass in Drupal 8

Defines a compiler pass to allow automatic override per backend.

A module developer has to tag a backend service with "backend_overridable":

custom_service:
  class: ...
  tags:
    - { name: backend_overridable }

As a site admin you set the 'default_backend' in your services.yml file:

parameters:
default_backend:
sqlite;

As a developer for alternative storage engines you register a service with $yourbackend.$original_service:

sqlite.custom_service:
  class: ...

Hierarchy

• class \Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass implements \Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface

2 files declare their use of BackendCompilerPass

BackendCompilerPassTest.php in core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php

Contains \Drupal\Tests\Core\DependencyInjection\Compiler\BackendCompilerPassTest.

CoreServiceProvider.php in core/lib/Drupal/Core/CoreServiceProvider.php

File

core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php, line 34

Namespace

Drupal\Core\DependencyInjection\Compiler

class BackendCompilerPass implements CompilerPassInterface {

  /**
   * {@inheritdoc}
   */
  public function process(ContainerBuilder $container) {
    if ($container
      ->hasParameter('default_backend')) {
      $default_backend = $container
        ->getParameter('default_backend');

      // Opt out from the default backend.
      if (!$default_backend) {
        return;
      }
    }
    else {
      try {
        $default_backend = $container
          ->get('database')
          ->driver();
        $container
          ->set('database', NULL);
      } catch (\Exception $e) {

        // If Drupal is not installed or a test doesn't define database there
        // is nothing to override.
        return;
      }
    }
    foreach ($container
      ->findTaggedServiceIds('backend_overridable') as $id => $attributes) {

      // If the service is already an alias it is not the original backend, so
      // we don't want to fallback to other storages any longer.
      if ($container
        ->hasAlias($id)) {
        continue;
      }
      if ($container
        ->hasDefinition("{$default_backend}.{$id}") || $container
        ->hasAlias("{$default_backend}.{$id}")) {
        $container
          ->setAlias($id, new Alias("{$default_backend}.{$id}"));
      }
    }
  }

}

Members

Name	Modifiers	Type	Description	Overrides
BackendCompilerPass::process	public	function	You can modify the container here before it is dumped to PHP code.