public function save($options = array()) {
    $json_attributes = $this->as_json_without_readonly_fields();

    if ($this->id) {
      return self::update($this->id, $json_attributes, $options);
    }
    else {
      if ($this->app && $this->app->id) {
        $new = self::create($this->app->id, $json_attributes, $options);
        $this->item_id = $new->item_id;
        return $this;
      }
      else {
        throw new PodioMissingRelationshipError('{"error_description":"Item is missing relationship to app"}', null, null);
      }
    }
  }