Groupby然後使用lambda/linq選擇數據

Question

我想使用下面的語句分組一些數據庫數據。

var res = from messages in db.Messages 
group messages by messages.Message_Sent_Date into grp 
select new { message_count = grp.Sum(g => g.Message_Count), message_cost = grp.Sum(g => g.Customer_Price) }; 

這相當於：

var query = db.Messages.Where(m => m.Message_Sent_Date != null && m.Message_Count != 99) 
         .GroupBy(d => d.Message_Sent_Date) 
         .Select(g => new { 
           message_count = g.Sum(c => c.Message_Count), 
           message_cost = g.Sum(c => c.Customer_Price), 
          }); 

我的問題是，所選擇的對象有2個字段即MESSAGE_COUNT和message_cost。如果我想添加第三個字段'Message_Sent_Date'，它基本上是數據分組到的列。我怎麼做？

Answer 1

使用g.Key這將是爲每個組Message_Sent_Date，因此片段將是這樣的：

// Modified select after the GroupBy clause 
.Select(g => 
     new 
     { 
      message_count = g.Sum(c => c.Message_Count), 
      message_cost = g.Sum(c => c.Customer_Price), 
      Message_Sent_Date= g.Key 
     });