Service Injection

When to Use

Inject services when your plugin needs functionality beyond what the base class provides, such as HTTP clients, external APIs, database access, or custom business logic services.

Decision

CRITICAL: EcaPluginBase has a FINAL constructor. You MUST use the parent::create() pattern.

Service Need	Injection Pattern	Why
Parent's services	DO NOT inject	Parent already has them (entity_type.manager, eca.token_services, logger, etc.)
Your custom services	Use `parent::create()` + inject	Extends parent's service set
Optional services	Inject + NULL default	Service may not exist

Pattern

use Symfony\Component\DependencyInjection\ContainerInterface;
use GuzzleHttp\ClientInterface;
use Drupal\eca\Service\YamlParser;

class MyAction extends ConfigurableActionBase {

  // Typed properties (PHP 8)
  protected ClientInterface $httpClient;
  protected YamlParser $yamlParser;
  protected ?MyCustomService $customService;

  /**
   * CRITICAL: Use parent::create(), NOT new static()
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition): static {
    // Create instance with parent's services
    $instance = parent::create($container, $configuration, $plugin_id, $plugin_definition);

    // Inject ONLY your new services
    $instance->httpClient = $container->get('http_client');
    $instance->yamlParser = $container->get('eca.service.yaml_parser');

    // Optional service with NULL fallback
    $instance->customService = $container->has('my_module.custom_service')
      ? $container->get('my_module.custom_service')
      : NULL;

    return $instance;
  }

  public function execute(): void {
    // Use injected services
    $response = $this->httpClient->request('GET', $url);
    $config = $this->yamlParser->parse($yaml_string);

    if ($this->customService) {
      $this->customService->performOperation();
    }
  }
}

Common Mistakes

Wrong: Using new static() with parent constructor args → Right: Fatal error (parent constructor is FINAL)
Wrong: Injecting parent's services again → Right: Duplicate dependencies, breaks when parent changes
Wrong: No typed properties → Right: Harder to debug, no IDE autocomplete
Wrong: Injecting in constructor instead of create() → Right: Bypasses Drupal's service container
Wrong: Not checking optional service existence → Right: Crashes when service not available

Service Injection

When to Use

Decision

Pattern

Common Mistakes

See Also