LINQ：用匿名類型處理

Question

我試圖生成表單的圖表：

User A User B  Owes  Owed  Net 
Sam  David  $20  $10  $10 
Timbo  ODP  $30  $0  $30 

使用下面的查詢：

 var debt = from user in users 
        select new { 
        Username = username, 
        User = user, 
        Owes = owedBetween(username, user), 
        Owed = owedBetween(user, username), 
        Net = Owes - Owed // doesn't compile 
        }; 

的問題是，最後行不編譯。有沒有辦法在查詢中設置Net值，還是必須將其初始化爲零，然後再進行更改？

Answer 1

嘗試使用let關鍵字：

var debt = from user in users 
       let owes = owedBetween(username, user) 
       let owed = owedBetween(user, username) 
       select new { 
       Username = username, 
       User = user, 
       Owes = owes, 
       Owed = owed, 
       Net = owes - owed 
       }; 

Answer 2

嘗試：

Net = owedBetween(username, user) - owedBetween(user, username) 

順便說一句，我建議你用更好的名稱爲username和user。哪個是哪個？