How to do dependency injection for ConstraintValidator?

Question

After upgrading to Drupal 10, running the coding standards check suggested that I could use DI in my validation constraints.

For example, this simple one:

<?php

declare(strict_types=1);

namespace Drupal\my_module\Plugin\Validation\Constraint;

use Drupal\Core\Logger\LoggerChannelFactoryInterface;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Validates the DateTimeMidnightOnly constraint.
 */
class DateTimeMidnightOnlyValidator extends ConstraintValidator {

  /**
   * {@inheritdoc}
   */
  public function validate(mixed $value, Constraint $constraint): void {
    foreach ($value as $item) {
      if (!$this->isMidnight($item->value)) {
        $item_value = $item->value;
        \Drupal::logger('my_custom_error_channel')->error("Invalid midnight timestamp! $item_value");
        $this->context->addViolation($constraint->notMidnight, ['%value' => $item_value]);
      }
    }
  }

  /**
   * Is the DateTime string midnight?
   *
   * @param string $value
   *   The DateTime string.
   *
   * @returns bool
   *   TRUE if it is a midnight string.
   */
  private function isMidnight(string $value): bool {
    return str_ends_with($value, 'T00:00:00');
  }

}

So I tried injecting the logger:

  /**
   * Logger factory.
   *
   * @var \Drupal\Core\Logger\LoggerChannelFactoryInterface
   */
  protected LoggerChannelFactoryInterface $loggerFactory;

  /**
   * Constructs DateTimeMidnightOnlyValidator.
   *
   * @param \Drupal\Core\Logger\LoggerChannelFactoryInterface $logger_factory
   *   The logger factory.
   */
  public function __construct(LoggerChannelFactoryInterface $logger_factory) {
    $this->loggerFactory = $logger_factory;
  }

This results in an error:

ArgumentCountError: Too few arguments to function Drupal\custom_module\Plugin\Validation\Constraint\DateTimeMidnightOnlyValidator::__construct(), 0 passed in /var/www/html/web/core/lib/Drupal/Core/DependencyInjection/ClassResolver.php on line 31 and exactly 1 expected

So I need to pass the argument-- how do I do that? For custom services I know I can use mymodule.services.yml, and for totally overriding core services I can use MyModuleServiceProvider.php, but what about validation constraints?

Answer 1

To pass the argument implement ContainerInjectionInterface::create().

For example:

class TaxonomyTermHierarchyConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {

  /**
   * The entity type manager.
   *
   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
   */
  private $entityTypeManager;

  /**
   * Creates a new TaxonomyTermHierarchyConstraintValidator instance.
   *
   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
   *   The entity type manager.
   */
  public function __construct(EntityTypeManagerInterface $entity_type_manager) {
    $this->entityTypeManager = $entity_type_manager;
  }

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

...

Example from /core/modules/taxonomy/src/Plugin/Validation/Constraint/TaxonomyTermHierarchyConstraintValidator.php