drupal-hook-patterns

Drupal Hook Patterns

Always prefer OOP hooks with #[Hook] attribute in Drupal 11+. Never put business logic directly in .module files — use services. Always check existing hook implementations before adding new ones to avoid conflicts.

OOP Hooks (Drupal 11+)

Hook Attribute Pattern

declare(strict_types=1);

namespace Drupal\my_module\Hook;

use Drupal\Core\Hook\Attribute\Hook;
use Drupal\Core\StringTranslation\StringTranslationTrait;

/**
 * Hook implementations for my_module.
 */
final class MyModuleHooks {

  use StringTranslationTrait;

  #[Hook('form_alter')]
  public function formAlter(array &$form, FormStateInterface $form_state, string $form_id): void {
    if ($form_id === 'node_article_form') {
      $form['title']['#description'] = $this->t('Enter a descriptive title.');
    }
  }

  #[Hook('entity_presave')]
  public function entityPresave(EntityInterface $entity): void {
    if ($entity->getEntityTypeId() === 'node' && $entity->bundle() === 'article') {
      // Set default values before saving.
    }
  }

}

Legacy Bridge (Drupal 10 Compatibility)

// my_module.module

use Drupal\Core\Hook\Attribute\LegacyHook;

/**
 * Implements hook_form_alter().
 */
#[LegacyHook]
function my_module_form_alter(array &$form, FormStateInterface $form_state, string $form_id): void {
  \Drupal::classResolver(MyModuleHooks::class)->formAlter($form, $form_state, $form_id);
}

Common Hooks

Form Alter

/**
 * Implements hook_form_FORM_ID_alter() for node_article_form.
 */
function my_module_form_node_article_form_alter(array &$form, FormStateInterface $form_state): void {
  // Add validation.
  $form['#validate'][] = '_my_module_article_validate';

  // Modify field widgets.
  $form['field_category']['widget']['#required'] = TRUE;
}

Entity Hooks

/**
 * Implements hook_entity_presave().
 */
function my_module_entity_presave(EntityInterface $entity): void {
  if ($entity instanceof NodeInterface && $entity->bundle() === 'event') {
    // Set computed field values.
  }
}

/**
 * Implements hook_entity_insert().
 */
function my_module_entity_insert(EntityInterface $entity): void {
  if ($entity instanceof NodeInterface) {
    // Post-creation actions (notifications, indexing).
  }
}

/**
 * Implements hook_entity_access().
 */
function my_module_entity_access(EntityInterface $entity, string $operation, AccountInterface $account): AccessResultInterface {
  if ($entity->getEntityTypeId() === 'node' && $entity->bundle() === 'private_content') {
    return AccessResult::forbiddenIf(
      $operation === 'view' && !$account->hasPermission('view private content')
    )->cachePerPermissions();
  }
  return AccessResult::neutral();
}

Theme Hooks

/**
 * Implements hook_theme().
 */
function my_module_theme(): array {
  return [
    'my_module_component' => [
      'variables' => [
        'title' => NULL,
        'items' => [],
        'attributes' => NULL,
      ],
    ],
  ];
}

/**
 * Implements hook_preprocess_HOOK() for node templates.
 */
function my_module_preprocess_node(array &$variables): void {
  $node = $variables['node'];
  if ($node->bundle() === 'article') {
    $variables['reading_time'] = _my_module_calculate_reading_time($node);
  }
}

Event Subscribers

declare(strict_types=1);

namespace Drupal\my_module\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;

final class MyEventSubscriber implements EventSubscriberInterface {

  public static function getSubscribedEvents(): array {
    return [
      KernelEvents::REQUEST => ['onRequest', 100],
    ];
  }

  public function onRequest(RequestEvent $event): void {
    // Handle incoming request.
  }

}

Install and Update Hooks

These hooks live in .install files, not .module files. They handle module lifecycle and database schema migrations.

/**
 * Implements hook_install().
 */
function my_module_install(): void {
  // Runs once when module is first enabled.
  // Set initial state, create default content, grant permissions.
}

/**
 * Implements hook_uninstall().
 */
function my_module_uninstall(): void {
  // Clean up state, delete variables, remove custom tables.
  \Drupal::state()->delete('my_module.last_run');
}

Update Hooks (Database Migrations)

Number update hooks sequentially. Each runs exactly once per environment. Keep them idempotent — safe to run on databases in any state.

/**
 * Add the 'priority' base field to my_entity.
 */
function my_module_update_10001(): void {
  $field = BaseFieldDefinition::create('integer')
    ->setLabel(t('Priority'))
    ->setDefaultValue(0);
  \Drupal::entityDefinitionUpdateManager()
    ->installFieldStorageDefinition('priority', 'my_entity', 'my_module', $field);
}

Post-Update Hooks (Data Migrations)

Use hook_post_update_NAME() for data changes that require the entity system to be fully updated. These run after all hook_update_N() hooks.

/**
 * Populate priority field with default values for existing entities.
 */
function my_module_post_update_set_default_priority(array &$sandbox): void {
  // Use batch processing for large datasets.
  if (!isset($sandbox['total'])) {
    $sandbox['ids'] = \Drupal::entityQuery('my_entity')->accessCheck(FALSE)->execute();
    $sandbox['total'] = count($sandbox['ids']);
    $sandbox['current'] = 0;
  }

  $batch = array_splice($sandbox['ids'], 0, 50);
  $storage = \Drupal::entityTypeManager()->getStorage('my_entity');
  foreach ($storage->loadMultiple($batch) as $entity) {
    $entity->set('priority', 0)->save();
    $sandbox['current']++;
  }

  $sandbox['#finished'] = $sandbox['total'] ? $sandbox['current'] / $sandbox['total'] : 1;
}

Hook Implementation Checklist

1. Prefer OOP hooks with #[Hook] attribute (Drupal 11+).
2. Provide #[LegacyHook] bridge for Drupal 10 compatibility.
3. Delegate hook logic to injectable services.
4. Keep .module file thin - hooks call services.
5. Use specific form alter hooks (hook_form_FORM_ID_alter) over generic.
6. Add cache metadata to access results.