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Defining Services

When to Use

When you need to register a new service with the Drupal container.

Steps

  1. Create the service class 

    // src/MyService.php
namespace Drupal\my_module;

use Drupal\Core\Database\Connection;
use Psr\Log\LoggerInterface;

class MyService {

  public function __construct(
    protected Connection $database,
    protected LoggerInterface $logger,
  ) {}

  public function doSomething() {
    $this->logger->info('Doing something');
  }
}

  2. Define the service in my_module.services.yml 

    services:
  my_module.my_service:
    class: Drupal\my_module\MyService
    arguments: ['@database', '@logger.channel.my_module']

  3. Clear cache to register the service 

    drush cr

  4. Use the service 

    // Via dependency injection (preferred)
$service = $container->get('my_module.my_service');

// Via static helper (procedural code only)
$service = \Drupal::service('my_module.my_service');

Decision Points

At this step... If... Then...
Defining service ID Service is public API Use semantic name: my_module.manager
Defining service ID Service is internal Use FQCN or my_module.internal.name
Choosing arguments Dependency is required Constructor injection via arguments:
Choosing arguments Dependency is optional Setter injection via calls:
Setting public/private Service used by other modules public: true (default)
Setting public/private Service is internal to module public: false

Common Mistakes

  • Not clearing cache after adding service — Service won't be available until cache rebuild
  • Circular dependencies — Service A depends on B, B depends on A (container will throw exception)
  • Injecting deprecated services — Check for deprecation notices; use modern replacements
  • Mixing public and private concerns — Keep public API services separate from internal implementation services
  • Not using interfaces — Type-hint against interfaces (LoggerInterface) not concrete classes for flexibility

See Also