protected function getDataArray() {
    return array(
      'created_at' => $this->time,
      'type' => $this->type,
      'sub_type' => empty($this->sub_type) ? '' : $this->sub_type,
      'content_id' => empty($this->content_id) ? 0 : $this->content_id,
      'content_title' => empty($this->content_title) ? '' : $this->content_title,
      'library_name' => empty($this->library_name) ? '' : $this->library_name,
      'library_version' => empty($this->library_version) ? '' : $this->library_version
    );
  }