/// <summary>
 /// 读取可空日期型值
 /// </summary>
 /// <param name="row">数据行</param>
 /// <param name="columns">列集合</param>
 /// <param name="columnName">列名称</param>
 /// <returns>日期型结果</returns>
 protected DateTimeOffset?LoadNullableDateTimeOffset(DataRow row, DataColumnCollection columns, String columnName)
 {
     if (columns.Contains(columnName) && !Convert.IsDBNull(row[columnName]))
     {
         return(DbConvert.ToDateTimeOffset(row[columnName]));
     }
     else
     {
         return(null);
     }
 }
 /// <summary>
 /// 读取可空日期型值
 /// </summary>
 /// <param name="args">对象创建参数</param>
 /// <param name="columnName">列名称</param>
 /// <returns>日期型结果</returns>
 protected DateTimeOffset?LoadNullableDateTimeOffset(EntityCreatingArgs args, String columnName)
 {
     if (args.Columns.Contains(columnName) && !DbConvert.IsDBNull(args.Row[columnName]))
     {
         return(DbConvert.ToDateTimeOffset(args.Row[columnName]));
     }
     else
     {
         return(null);
     }
 }