什麼是Linq lambda表達式（GROUP_CONCAT）中的XML PATH和Stuff的等價物？

Question

我有一個表是這樣的：

EmployeeId EmployeeName ItemName 
4   Ganesh  Key Board 
4   Ganesh  Processor 
1   Jignesh  Key Board 
1   Jignesh  Mouse 
1   Jignesh  Processor 
3   Rakesh  Key Board 
2   Tejas  Key Board 
2   Tejas  Mouse 
2   Tejas  Processor 

我需要查詢這彷彿是ITEMNAME不同的相同employeeid和employeename我們應該有項目，如「」分開。

喜歡的人這是如下：

EmployeeId EmployeeName ItemName 
1   Jignesh  Key Board, Mouse, Processor 
2   Tejas  Key Board, Mouse, Processor 
3   Rakesh  Key Board 
4   Ganesh  Key Board, Processor 

這裏是SQL查詢此：

誰能幫我轉換上述SQL查詢到Lambda表達式？

Answer 1

我假設你的意思是一個Linq語句（例如EF或Linq2Sql）Lambda expression。

該FOR XML PATH和STUFF示例顯示是一種解決辦法缺乏GROUP_CONCAT or LISTAGG in Sql Server。

你並不需要在所有重現黑客在LINQ - 相反，只需加載所有行的目標集合到內存中，GroupBy所需的關鍵員工，然後在選擇投影使用String.Join：

var result = db.EmployeeItems 
     // If you have a filter add the .Where() here ... 
     .GroupBy(e => e.EmployeeId) 
     .ToList() 
     // Because the ToList(), this select projection is not done in the DB 
     .Select(eg => new 
     { 
      EmployeeId = eg.Key, 
      EmployeeName = eg.First().EmployeeName, 
      Items = string.Join(",", eg.Select(i => i.ItemName)) 
     }); 

凡employeeItems是投影Employee和Items之間的連接：

var employeeItems = new [] 
{ 
    new EmployeeItem{EmployeeId = 1, EmployeeName = "Ganesh", ItemName = "Keyboard"}, 
    new EmployeeItem{EmployeeId = 1, EmployeeName = "Ganesh", ItemName = "Mouse"}, 
    new EmployeeItem{EmployeeId = 2, EmployeeName = "John", ItemName = "Keyboard"} 
}; 

結果：

1 Ganesh Keyboard,Mouse 
2 John Keyboard