public function as_json_without_readonly_fields() {
    $readonly_fields = $this->fields->readonly_fields()->external_ids();
    $json_attributes = $this->as_json(false);
    foreach ($this->fields->readonly_fields()->external_ids() as $external_id) {
      if (isset($json_attributes['fields'][$external_id])) {
        unset($json_attributes['fields'][$external_id]);
      }
    }
    return $json_attributes;
  }