HOW TO：處理查詢中的複合索引鍵 (LINQ to SQL)
更新： November 2007
有些運算子只能取用一個引數。如果引數必須包括資料庫中的多個資料行，則必須建立匿名型別來表示此項組合。
範例
下列範例顯示叫用 (Invoke) GroupBy 運算子的查詢，這個運算子只可以取用一個 key 引數。
Dim query = _
From cust In db.Customers _
Group cust.ContactName By Key = New With {cust.City, cust.Region} _
Into Group
For Each grp In query
Console.WriteLine("Location Key: {0}", grp.Key)
For Each listing In grp.Group
Console.WriteLine(vbTab & "0}", listing)
Next
Next
var query =
from cust in db.Customers
group cust.ContactName by new { City = cust.City, Region = cust.Region };
foreach (var grp in query)
{
Console.WriteLine("\nLocation Key: {0}", grp.Key);
foreach (var listing in grp)
{
Console.WriteLine("\t{0}", listing);
}
}
聯結 (Join) 的情況也相同，如下列範例所示：
Dim query = From ord In db.Orders, prod In db.Products _
Join det In db.OrderDetails _
On New With {ord.OrderID, prod.ProductID} Equals _
New With {det.OrderID, det.ProductID} _
Select ord.OrderID, prod.ProductID, det.UnitPrice
var query =
from ord in db.Orders
from prod in db.Products
join det in db.OrderDetails
on new { ord.OrderID, prod.ProductID } equals new { det.OrderID, det.ProductID }
into details
from det in details
select new { ord.OrderID, prod.ProductID, det.UnitPrice };