Relationship.php

<?php

namespace Drupal\jsonapi\JsonApiResource;

use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Field\EntityReferenceFieldItemListInterface;
use Drupal\Core\Url;
use Drupal\jsonapi\JsonApiSpec;
use Drupal\jsonapi\ResourceType\ResourceType;
use Drupal\jsonapi\Routing\Routes;

/**
 * Represents references from one resource object to other resource object(s).
 *
 * @internal JSON:API maintains no PHP API since its API is the HTTP API. This
 *   class may change at any time and this will break any dependencies on it.
 *
 * @see https://www.drupal.org/project/drupal/issues/3032787
 * @see jsonapi.api.php
 */
class Relationship implements TopLevelDataInterface {

  /**
   * The context resource object of the relationship.
   *
   * A relationship object represents references from a resource object in
   * which it’s defined to other resource objects. Respectively, the "context"
   * of the relationship and the "target(s)" of the relationship.
   *
   * A relationship object's context either comes from the resource object that
   * contains it or, in the case that the relationship object is accessed
   * directly via a relationship URL, from its `self` URL, which should identify
   * the resource to which it belongs.
   *
   * @var \Drupal\jsonapi\JsonApiResource\ResourceObject
   *
   * @see https://jsonapi.org/format/#document-resource-object-relationships
   * @see https://jsonapi.org/recommendations/#urls-relationships
   */
  protected $context;

  /**
   * The data of the relationship object.
   *
   * @var \Drupal\jsonapi\JsonApiResource\RelationshipData
   */
  protected $data;

  /**
   * The relationship's public field name.
   *
   * @var string
   */
  protected $fieldName;

  /**
   * The relationship object's links.
   *
   * @var \Drupal\jsonapi\JsonApiResource\LinkCollection
   */
  protected $links;

  /**
   * The relationship object's meta member.
   *
   * @var array
   */
  protected $meta;