如何使用linq在選擇查詢中獲取值？

Question

我已經使用LINQ內部連接合並了2個表客戶端和付款。在此之後，我用這兩個表中的值填寫一個新模型「總計」。我只需要獲得Username。有任何想法嗎？我會非常感謝！

var results = from client in _db.Clients 
          join trade in _db.Payments on client.Id equals trade.ClientId 
          where (client.Id == trade.ClientId && 
          DateTime.Compare(trade.TradeDate, (DateTime)fromDate) >= 0 && 
          DateTime.Compare(trade.TradeDate, (DateTime) toDate) <= 0) 
          select new { client.Username, trade}; 
      var cs = results 
       .GroupBy(tr => tr.trade.ClientId) 
       .Select(item => new Totals 
       { 
        Username = //here I need to set a value 
        CommBcf = item.Sum(client => client.trade.CommBcf), 
        EcnAll = item.Sum(client => client.trade.EcnAll), 
        EcnRbt = item.Sum(client => client.trade.EcnRbt), 
        OpenGross = item.Sum(client => client.trade.OpenGross), 
        CloseGross = item.Sum(client => client.trade.CloseGross) 
}).ToList(); 

Answer 1

按鍵和名稱分組。您可以通過使用new {id,name}創建新的匿名對象來對多列進行分組。

var results = from client in _db.Clients 
           join trade in _db.Payments on client.Id equals trade.ClientId 
           where (client.Id == trade.ClientId && 
           DateTime.Compare(trade.TradeDate, (DateTime)fromDate) >= 0 && 
           DateTime.Compare(trade.TradeDate, (DateTime) toDate) <= 0) 
           select new { client.Username, trade}; 
       var cs = results 
        .GroupBy(tr => new {id=tr.trade.ClientId,name=tr.trade.Name}) 
        .Select(item => new Totals 
        { 
         Username = item.Key.name 
         CommBcf = item.Sum(client => client.trade.CommBcf), 
         EcnAll = item.Sum(client => client.trade.EcnAll), 
         EcnRbt = item.Sum(client => client.trade.EcnRbt), 
         OpenGross = item.Sum(client => client.trade.OpenGross), 
         CloseGross = item.Sum(client => client.trade.CloseGross) 
    }).ToList();