child_entity

This module helps you to create Entities which creating them depends on a parent entity.

Consider a Room in a House. The Room can only every be in one house. In this example Room is child and House is parent entity.

In order to use this module you have to:

• Implement ChildEntityInterface or extend it
• Use Child Entity Handlers, either directly in the Entity definition or extending them.
• Define parent key in entity_keys section of the child entity annotation and use ChildEntityTrait
• Add childBaseFieldDefinitions

This works in the same way as core's EntityOwnerTrait.

/**
 ************ other configuration ************
 *   handlers = {
 *     "list_builder" = "Drupal\child_entity\ChildEntityListBuilder",
 *     "views_data" = "Drupal\child_entity\ChildEntityViewsData",
 *     "form" = {
 *       "default" = "Drupal\child_entity\Form\ChildEntityForm",
 *     },
 *     "route_provider" = {
 *       "html" = "Drupal\child_entity\Routing\ChildEntityHtmlRouteProvider",
 *     },
 *     "access" = "Drupal\child_entity\ChildEntityAccessControlHandler",
 *   entity_keys = {
 *     "parent" = "house",
 *   },
 ************ other configuration ************
 */
class Room extends ContentEntityBase implements ChildEntityInterface {

  use ChildEntityTrait;

  /**
   * {@inheritdoc}
   */
  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
    $fields = parent::baseFieldDefinitions($entity_type);

    $fields += static::childBaseFieldDefinitions($entity_type);

    return $fields;
  }
}

Revision-able Entities and urlRouteParameters()

If your entity type also has revisions you may be overriding the urlRouteParameters() but you need to specify to use the one from the trait:

  use ChildEntityTrait {
    urlRouteParameters as childEntityUrlRouteParameters;
  }

  /**
   * {@inheritdoc}
   * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException
   */
  protected function urlRouteParameters($rel) {
    $uri_route_parameters = $this->childEntityUrlRouteParameters($rel);

    if ($rel === 'revision_revert' && $this instanceof RevisionableInterface) {
      $uri_route_parameters[$this->getEntityTypeId() . '_revision'] = $this->getRevisionId();
    }
    elseif ($rel === 'revision_delete' && $this instanceof RevisionableInterface) {
      $uri_route_parameters[$this->getEntityTypeId() . '_revision'] = $this->getRevisionId();
    }

    return $uri_route_parameters;
  }

Version 1

Version 1 of this module implemented Base classes that can be extended however this has limitations and version 2 uses Traits which allows the following:

class ChildNode extends Node implements ChildEntityInterface {

  use ChildEntityTrait;
}