Drupal and Web Development Tidbits

Custom Classes and Dependency Injection

November 11, 2021

Written by: Jon Kamke

Stop making everything a service just to use DI and start implementing ContainerInjectionInterface

Using dependency injection with services is fairly straightforward and common place, but dependency injection (DI) with a custom class that’s not a service is not seen very often in Drupal core. Stop making everything a service just to use DI and start implementing ContainerInjectionInterface and instantiate with \Drupal::classResolver();.

Below is an example custom class that implements ContainerInjectionInterface to inject the my_module.service service:

<?php

namespace Drupal\my_module\Entity;

use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
use Drupal\kraken_traceability\Service\MapService;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Define the data structure for a location.
 */
class LocationEntity implements ContainerInjectionInterface {

  /**
   * MapIngredientsService.
   *
   * @var \Drupal\my_module\Service\MapIngredientsService
   */
  private $mapService;

  /**
   * Constructs a new LocationEntity.
   *
   * @param \Drupal\my_module\Service\MapService $mapService
   *   MapIngredientsService.
   */
  public function __construct(MapService $mapService) {
    $this->mapService = $mapService;
  }

  /**
   * @inheritdoc
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('my_module.service'),
    );
  }

}

In a *.module file, for example, we can not instantiate this class with the new keyword like new LocationEntity() but instead use \Drupal::classResolver(); (see Drupal API for more info).

  $locationEntity = \Drupal::classResolver(LocationEntity::class);

Custom