csharp: DBNull and DateTime

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/// <summary>         ///         /// </summary>         /// <param name="dateTime"></param>         /// <returns></returns>         public DateTime CheckDBNull(object dateTime)         {             if (dateTime == DBNull.Value)                 return DateTime.MinValue;             else                 return (DateTime)dateTime;         }         /// <summary>         ///         /// </summary>         /// <param name="field"></param>         /// <param name="data"></param>         /// <returns></returns>         public DateTime? ReadNullableDateTimefromReader(string field, IDataRecord data)         {               var a = data[field];             if (a != DBNull.Value)             {                 return Convert.ToDateTime(a);             }             return null;         }         /// <summary>         ///         /// </summary>         /// <param name="field"></param>         /// <param name="data"></param>         /// <returns></returns>         public DateTime ReadDateTimefromReader(string field, IDataRecord data)         {             DateTime value;             var valueAsString = data[field].ToString();             try             {                 value = DateTime.Parse(valueAsString);             }             catch (Exception)             {                 throw new Exception("Cannot read Datetime from reader");             }               return value;         }     }

　　

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menu.IsMainMenu = (!DBNull.Equals(reader["IsMainMenu"], null)) ? (bool)reader["IsMainMenu"] : true;                         menu.Remark = (!DBNull.Equals(reader["Remark"], null)) ? (string)reader["Remark"].ToString() : "";                         menu.ParentMenuId = (!DBNull.Equals(reader["ParentMenuId"], null)) ? (int)reader["ParentMenuId"] : 0;                         menu.TreeLevel = (!DBNull.Equals(reader["TreeLevel"], null)) ? (int)reader["TreeLevel"] : 0;                         menu.SortIndex = (!DBNull.Equals(reader["SortIndex"], null)) ? (int)reader["SortIndex"] : 0;                         menu.CreatedOn = CheckDBNull(reader["CreatedOn"]);// (!object.Equals(reader["CreatedOn"], null)) ? (DateTime)reader["CreatedOn"] : DateTime.Now;

　　https://github.com/mathnet