public static Traderate ToObject(string str)
    {
        if (str == null || str.Equals(String.Empty))
        {
            return(null);
        }
        JsonData jd = JsonMapper.ToObject(str);

        return(new Traderate((int)jd[Param.TID], (long)jd[Param.NUM_IID],
                             Traderate.StringToROLE((string)jd[Param.ROLE]), (string)jd[Param.NICK],
                             Traderate.StringToRateResult((string)jd[Param.RESULT]),
                             StringUtil.StringToDateTime((string)jd[Param.CREATED]),
                             (string)jd[Param.CONTENT], (string)jd[Param.REPLY]));
    }