Overriding the default handlers for any entity in Drupal 8

Drupal 8 has a lot of things in core which makes a developer life easier, and Annotations are one of them. Annotation is a discovery mechanism similar to info hooks in Drupal 7.

Entities declare handlers which takes care of different functions like Access, Storage , List building etc. in annotations.

Let’s take an example of User Entity.

Below are the handlers declared in User Entity annotation.

handlers = {
     "storage" = "Drupal\user\UserStorage",
     "storage_schema" = "Drupal\user\UserStorageSchema",
     "access" = "Drupal\user\UserAccessControlHandler",
     "list_builder" = "Drupal\user\UserListBuilder",
     "views_data" = "Drupal\user\UserViewsData",
     "route_provider" = {
       "html" = "Drupal\user\Entity\UserRouteProvider",
     },
     "form" = {
       "default" = "Drupal\user\ProfileForm",
       "cancel" = "Drupal\user\Form\UserCancelForm",
       "register" = "Drupal\user\RegisterForm"
     },
     "translation" = "Drupal\user\ProfileTranslationHandler"
}

Now say we want to override access handler for User entity. We can use hook_entity_type_alter to alter the class for handler.

/**
 * Implements hook_entity_type_alter().
 */
function MY_MODULE_entity_type_alter(array &$entity_types) {
  $entity_types['user']->setHandlerClass('access', CustomAccessHandler::class);
}

Now you can create your own Access handler at MY_MODULE/src/CustomAccessHandler.

You can either extend the EntityAccessControlHandler class or extend the default handler ie., UserAccessControlHandler in our case and just override your required function.

<?php

namespace Drupal\MY_MODULE;

use Drupal\user\UserAccessControlHandler;

/**
 * Defines the custom access control handler for the user entity type.
 */
class CustomAccessHandler extends UserAccessControlHandler {

  /**
   * {@inheritdoc}
   */
  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
   // Custom override code.
  }

}

Remember to rebuild your caches after this.