Linq上的多列組

Question

我想在多列上使用組，但是，無法理解我該如何選擇SAMPLE_TIME，即使我寫曼紐爾日期來取樣時間，我得到以下錯誤;

System.InvalidCastException: 'System.ValueTuple`2[System.String,System.String]' 'System.String' 

目前我使用的是如下所示;

var dt = (from dr1 in dtTopAll.AsEnumerable() 
          where dr1.Field<DateTime>("SAMPLE_TIME") <= maxDate 
          group dr1 by ("WAIT_CLASS", "SAMPLE_TIME") into g 
          select new 
          { 
           SAMPLE_TIME = // How can i select sample_time, 
           WAIT_CLASS = g.Key, 
           WAITS = g.Sum(z => z.Field<double>("WAITS")/100) 
          }).ToDataTable(); 

Answer 1

你有沒有嘗試過這樣的：

var dt = (from dr1 in dtTopAll.AsEnumerable() 
      where dr1.Field<DateTime>("SAMPLE_TIME") <= maxDate 
      group dr1 by new 
         { 
          WAIT_CLASS = dr1.Field<string>("WAIT_CLASS"), 
          SAMPLE_TIME = dr1.Field<DateTime>("SAMPLE_TIME") 
         } into g 
      select new 
        { 
         SAMPLE_TIME = g.Key.SAMPLE_TIME, 
         WAIT_CLASS = g.Key.WAIT_CLASS, 
         WAITS = g.Sum(z => z.Field<double>("WAITS")/100) 
        }).ToDataTable(); 

Answer 2

你需要什麼是使用GROUP BY新的，如果你要選擇你可以使用你的別名創建組新的匿名類型。請檢查這個; Group By Multiple Column In LINQ in C#