如何使用Lambda返回不同行的分組數組

Question

我想從表中選擇行。我需要在一列上執行GroupBy，然後在不同的列上執行Distinct（）。我想返回結果中的整個行。

假設一個數據庫表具有以下結構和數據：

GroupId = 1, To = "A", From = "B", Flag = True 
GroupId = 1, To = "A", From = "C", Flag = True 
GroupId = 1, To = "B", From = "A", Flag = True 
GroupId = 1, To = "B", From = "C", Flag = False 
GroupId = 1, To = "C", From = "A", Flag = True 
GroupId = 1, To = "C", From = "B", Flag = True 
GroupId = 2, To = "A", From = "B", Flag = True 
GroupId = 2, To = "B", From = "C", Flag = True 
GroupId = 2, To = "C", From = "A", Flag = True 
GroupId = 2, To = "D", From = "C", Flag = True 
GroupId = 2, To = "D", From = "A", Flag = False 
GroupId = 2, To = "A", From = "B", Flag = True 

下面的代碼行返回組的陣列與每個含To字符串數組：

var test = db.LookupMap 
    .Where(u => u.Flag == true) 
    .GroupBy(u => u.GroupId, (key, group) => group.Select(m => m.To).Distinct()) 
    .ToArray(); 

我可以通過將m.To更改爲m獲取一組對象：

.GroupBy(u => u.GroupId, (key, group) => group.Select(m => m).Distinct()) 

但是這會打破「收件人」列上的Distinct（）。

如何返回對象數組（整行）而不是數組字符串？

注意：要列應爲唯一的GroupId不同

Answer 1

使用另一個GroupBy與First結合：

.GroupBy(u => u.GroupId, 
     (key, group) => group.GroupBy(m => m.To).Select(g => g.First())) 

這組項目，而不使用To屬性值第一組，然後進行第一個項目從每一個內部組。這是從moreLINQ獲得相當於DistinctBy方法的最簡單方法 - 獲取整行，但Distinct應該只在一個屬性值上運行。