fieldAccess example

      if ((($this->options['delta_limit'] > 0) && ($this->options['delta_limit'] != $cardinality)) || intval($this->options['delta_offset'])) {
        $this->limit_values = TRUE;
      }
    }
  }

  /** * {@inheritdoc} */
  public function access(AccountInterface $account) {
    $access_control_handler = $this->entityTypeManager->getAccessControlHandler($this->getEntityType());
    return $access_control_handler->fieldAccess('view', $this->getFieldDefinition(), $account);
  }

  /** * Called to add the field to a query. * * By default, all needed data is taken from entities loaded by the query * plugin. Columns are added only if they are used in groupings. */
  public function query($use_groupby = FALSE) {
    $fields = $this->additional_fields;
    // No need to add the entity type.

$definitions = $this->fieldManager->getFieldDefinitions($resource_type->getEntityTypeId(), $resource_type->getBundle());
    assert(isset($definitions[$internal_field_name]), 'The field name should have already been validated.');
    $field_definition = $definitions[$internal_field_name];
    $filter_access_results = $this->moduleHandler->invokeAll('jsonapi_entity_field_filter_access', [$field_definition, $this->currentUser]);
    $filter_access_result = array_reduce($filter_access_results, function DAccessResultInterface $combined_result, AccessResultInterface $result) {
      return $combined_result->orIf($result);
    }, AccessResult::neutral());
    if (!$filter_access_result->isNeutral()) {
      return $filter_access_result;
    }
    $entity_access_control_handler = $this->entityTypeManager->getAccessControlHandler($resource_type->getEntityTypeId());
    $field_access = $entity_access_control_handler->fieldAccess('view', $field_definition, NULL, NULL, TRUE);
    return $filter_access_result->orIf($field_access);
  }

}

public function __unset($property_name) {
    if ($item = $this->first()) {
      $item->__unset($property_name);
    }
  }

  /** * {@inheritdoc} */
  public function access($operation = 'view', AccountInterface $account = NULL, $return_as_object = FALSE) {
    $access_control_handler = \Drupal::entityTypeManager()->getAccessControlHandler($this->getEntity()->getEntityTypeId());
    return $access_control_handler->fieldAccess($operation, $this->getFieldDefinition(), $account, $this, $return_as_object);
  }

  /** * {@inheritdoc} */
  public function defaultAccess($operation = 'view', AccountInterface $account = NULL) {
    // Grant access per default.     return AccessResult::allowed();
  }

  /** * {@inheritdoc} */

assert(is_null($entity) ||
      $field_definition->getTargetEntityTypeId() === $entity->getEntityTypeId() &&
      // Base fields do not have target bundles.       (is_null($field_definition->getTargetBundle()) || $field_definition->getTargetBundle() === $entity->bundle())
    );
    $entity_type_manager = \Drupal::entityTypeManager();
    $entity_access_control_handler = $entity_type_manager->getAccessControlHandler($field_definition->getTargetEntityTypeId());
    $bundle = $entity_type_manager->getDefinition($field_definition->getTargetEntityTypeId())->hasKey('bundle') ? $field_definition->getTargetBundle() : NULL;
    $entity_access_result = $entity
      ? $entity_access_control_handler->access($entity, 'update', $account, TRUE)
      : $entity_access_control_handler->createAccess($bundle, $account, [], TRUE);
    $field_access_result = $entity_access_control_handler->fieldAccess('edit', $field_definition, NULL, NULL, TRUE);
    return $entity_access_result->andIf($field_access_result);
  }

  /** * Streams file upload data to temporary file and moves to file destination. * * @return string * The temp file path. * * @throws \Symfony\Component\HttpKernel\Exception\HttpException * Thrown when input data cannot be read, the temporary file cannot be * opened, or the temporary file cannot be written. */

->method('getName')
      ->willReturn($field);

    $this->items
      ->expects($this->any())
      ->method('getEntity')
      ->willReturn($this->{$target});

    foreach (['view' => $view, 'edit' => $edit] as $operation => $result) {
      $result_text = !isset($result) ? 'null' : ($result ? 'true' : 'false');
      $message = "User '$field' field access returns '$result_text' with operation '$operation' for '$viewer' accessing '$target'";
      $this->assertSame($result, $this->accessControlHandler->fieldAccess($operation, $field_definition, $this->{$viewer}, $this->items), $message);
    }
  }

  /** * Ensures user name access is working properly. * * @dataProvider userNameProvider */
  public function testUserNameAccess($viewer, $target, $view, $edit) {
    $this->assertFieldAccess('name', $viewer, $target, $view, $edit);
  }

  

    /** @var \Drupal\Core\Field\FieldDefinitionInterface $field_definition */
    $field_definition = $field_definitions[$field_name];
    if ($field_definition->getSetting('target_type') !== 'file') {
      throw new AccessDeniedHttpException(sprintf('"%s" is not a file field', $field_name));
    }

    $entity_access_control_handler = $this->entityTypeManager->getAccessControlHandler($entity_type_id);
    $bundle = $this->entityTypeManager->getDefinition($entity_type_id)->hasKey('bundle') ? $bundle : NULL;
    $access_result = $entity_access_control_handler->createAccess($bundle, NULL, [], TRUE)
      ->andIf($entity_access_control_handler->fieldAccess('edit', $field_definition, NULL, NULL, TRUE));
    if (!$access_result->isAllowed()) {
      throw new AccessDeniedHttpException($access_result->getReason());
    }

    return $field_definition;
  }

  /** * Validates the file. * * @todo this method is unused in this class because file validation needs to * be split up in 2 steps in ::post(). Add a deprecation notice as soon as a * central core file upload service can be used in this class. * See https://www.drupal.org/project/drupal/issues/2940383 * * @param \Drupal\file\FileInterface $file * The file entity to validate. * @param array $validators * An array of upload validators to pass to file_validate(). * * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException * Thrown when there are file validation errors. */

/** * Tests field access. * * Regression test to verify that fieldAccess() can be called while only * passing the required parameters. * * @see https://www.drupal.org/node/2404739 */
  public function testFieldAccess() {
    $access_control_handler = \Drupal::entityTypeManager()->getAccessControlHandler($this->entityType);
    $this->assertTrue($access_control_handler->fieldAccess('view', $this->field));
  }

}

$field_definition = $items->getFieldDefinition();

    // Check that the field is an entity reference, or subclass of it, since we     // need to check the target_type setting.     if (!$items instanceof EntityReferenceFieldItemList) {
      throw new \LogicException('Expected the media library to be opened by an entity reference field.');
    }
    if ($field_definition->getFieldStorageDefinition()->getSetting('target_type') !== 'media') {
      throw new \LogicException('Expected the media library to be opened by an entity reference field that target media items.');
    }

    $field_access = $access_handler->fieldAccess('edit', $field_definition, $account, $items, TRUE);
    $access = $entity_access->andIf($field_access);
    if ($access instanceof RefinableCacheableDependencyInterface) {
      $access->addCacheableDependency($state);
    }
    return $access;
  }

  /** * {@inheritdoc} */
  public function getSelectionResponse(MediaLibraryState $state, array $selected_ids) {