getVersionIdentifier example

    $public_field_name = $resource_relationship->getPublicName();
    $relationship_route_name = Routes::getRouteName($resource_type, "$public_field_name.relationship.get");
    $links = [
      'self' => Url::fromRoute($relationship_route_name, ['entity' => $relationship_context->getId()]),
    ];
    if (static::hasNonInternalResourceType($resource_type->getRelatableResourceTypesByField($public_field_name))) {
      $related_route_name = Routes::getRouteName($resource_type, "$public_field_name.related");
      $links['related'] = Url::fromRoute($related_route_name, ['entity' => $relationship_context->getId()]);
    }
    if ($resource_type->isVersionable()) {
      $version_query_parameter = [JsonApiSpec::VERSION_QUERY_PARAMETER => $relationship_context->getVersionIdentifier()];
      $links['self']->setOption('query', $version_query_parameter);
      if (isset($links['related'])) {
        $links['related']->setOption('query', $version_query_parameter);
      }
    }
    return $links;
  }

  /** * Determines if a given list of resource types contains a non-internal type. * * @param \Drupal\jsonapi\ResourceType\ResourceType[] $resource_types * The JSON:API resource types to evaluate. * * @return bool * FALSE if every resource type is internal, TRUE otherwise. */

  protected static function buildLinkCollectionFromEntityReferenceField(ResourceObject $context, EntityReferenceFieldItemListInterface $field, LinkCollection $links) {
    $context_resource_type = $context->getResourceType();
    $public_field_name = $context_resource_type->getPublicName($field->getName());
    if ($context_resource_type->isLocatable() && !$context_resource_type->isInternal()) {
      $context_is_versionable = $context_resource_type->isVersionable();
      if (!$links->hasLinkWithKey('self')) {
        $route_name = Routes::getRouteName($context_resource_type, "$public_field_name.relationship.get");
        $self_link = Url::fromRoute($route_name, ['entity' => $context->getId()]);
        if ($context_is_versionable) {
          $self_link->setOption('query', [JsonApiSpec::VERSION_QUERY_PARAMETER => $context->getVersionIdentifier()]);
        }
        $links = $links->withLink('self', new Link(new CacheableMetadata(), $self_link, 'self'));
      }
      $has_non_internal_resource_type = array_reduce($context_resource_type->getRelatableResourceTypesByField($public_field_name), function D$carry, ResourceType $target) {
        return $carry ?: !$target->isInternal();
      }, FALSE);
      // If a `related` link was not provided, automatically generate one from       // the relationship object to the collection resource with all of the       // resources targeted by this relationship. However, that link should       // *not* be generated if all of the relatable resources are internal.       // That's because, in that case, a route will not exist for it.