與LINQ不同

Question

var sourceId = 
      (from workstation in db.station 
      join letter in db.letter on workstation.id equals letter.Site_Id 
      where ThatDate < DateTime.Now.AddYears(-1) 
      select workstatio).ToList(); 

這會產生一個列表，它將打印出重複如果不止一個，我該如何使用.distinct？

請指教，謝謝

Answer 1

var sourceId = 
      (from workstation in db.station 
      join letter in db.letter on workstation.id equals letter.Site_Id 
      where ThatDate < DateTime.Now.AddYears(-1) 
      select workstation).Distinct().ToList(); 

看看這個

http://msdn.microsoft.com/en-us/library/bb338049.aspx

Answer 2

你可能想在MoreLinq看看DistinctBy方法。你可以在哪裏傳遞一個lambda表達式作爲參數。

在你的榜樣，將類似於這樣：

var sourceId = 
     (from workstation in db.station 
     join letter in db.letter on workstation.id equals letter.Site_Id 
     where ThatDate < DateTime.Now.AddYears(-1) 
     select workstatio).DistinctBy(ws => ws.Id).ToList(); 

您還可以使用DistinctBy具有多個屬性：

var sourceId = 
     (from workstation in db.station 
     join letter in db.letter on workstation.id equals letter.Site_Id 
     where ThatDate < DateTime.Now.AddYears(-1) 
     select workstatio).DistinctBy(ws => new {Id = ws.Id, OtherProperty = ws.OtherProperty}).ToList(); 

順便說一句，而不是參考比較，匿名平等類型實例是通過比較其每個屬性來確定的。

我最近在Anders Hejlsberg本人建議解決此問題的方法中發現了一個有趣的討論。你可以閱讀它here.