toIncludeTree example

  public function resolve($data, $include_parameter) {
    assert($data instanceof ResourceObject || $data instanceof ResourceObjectData);
    $data = $data instanceof ResourceObjectData ? $data : new ResourceObjectData([$data], 1);
    $include_tree = static::toIncludeTree($data, $include_parameter);
    return IncludedData::deduplicate($this->resolveIncludeTree($include_tree, $data));
  }

  /** * Receives a tree of include field names and resolves resources for it. * * This method takes a tree of relationship field names and JSON:API Data * object. For the top-level of the tree and for each entity in the * collection, it gets the target entity type and IDs for each relationship * field. The method then loads all of those targets and calls itself * recursively with the next level of the tree and those loaded resources. * * @param array $include_tree * The include paths, represented as a tree. * @param \Drupal\jsonapi\JsonApiResource\Data $data * The entity collection from which includes should be resolved. * @param \Drupal\jsonapi\JsonApiResource\Data|null $includes * (Internal use only) Any prior resolved includes. * * @return \Drupal\jsonapi\JsonApiResource\Data * A JSON:API Data of included items. * * @throws \Drupal\Component\Plugin\Exception\PluginNotFoundException * Thrown if an included entity type doesn't exist. * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException * Thrown if a storage handler couldn't be loaded. */