Aggregate, LINQ, c#

The following code finds a list of Quantity values ok.

Question: At line 2, how aggregate could be applied to this code to get total quantity?

            Dim s List(Of Order)= (From o In db.Orders Where o.ID = 2).ToList()

            Dim sum = From o In s.OrderItems Select Total = o.Quantity

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LVL 34
Mike EghtebasDatabase and Application DeveloperAsked:
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Fernando SotoConnect With a Mentor RetiredCommented:
Hi eghtebas;

Try these out, it should give you what you are looking for.

'' Select Sum(o.Quantity) From tblOrders  o Where o.ID =2
Dim sumQuty = (From o In db.tblOrders
               Where o.ID = 2
               Select o.Quantity).Sum()

'' Select o,ID, Sum(o.Quantity) From tblOrders  Group By o.ID Having ID =2               
Dim sumQuty2 = From o In db.tblOrders
               Group o By ID = o.ID Into orderGroup = Group
               Where ID = 2
               Select ID, sumQuty = orderGroup.Sum(Function(q) q.Quantity)

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Are you looking for something like this:
Imports System.Linq

Module Module1
	Private orders As New List(Of Order) From _
	 { _
	  New Order() With {.ID = 1, .Quantity = 5}, _
	  New Order() With {.ID = 2, .Quantity = 12}, _
	  New Order() With {.ID = 3, .Quantity = 7}, _
	  New Order() With {.ID = 2, .Quantity = 2}, _
	  New Order() With {.ID = 1, .Quantity = 1}, _
	  New Order() With {.ID = 3, .Quantity = 8} _

	Sub Main()
		Console.WriteLine(String.Format("Quantity of Orders for OrderID 2 = {0}", (Aggregate order As Order In orders Where order.ID.Equals(2) Into Sum(order.Quantity))))
	End Sub
End Module

Class Order
	Property ID() As Integer
	Property Quantity() As Integer
End Class

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Produces the following output:Capture.JPG
Mike EghtebasDatabase and Application DeveloperAuthor Commented:
Hi Saige,

Orders is in Entity Framework define by db and has data in it.

Dim db As New TestDatabaseEntities

I want to pull that data. If I were doing it in SQL:

Select Sum(o.Quantity) From tblOrders  o Where o.ID =2


Select o,ID, Sum(o.Quantity) From tblOrders  Group By o.ID Having ID =2
it_saigeConnect With a Mentor DeveloperCommented:
Well you should still be able to use Aggregate, try:
'  This is the list of orders.
Dim s List(Of Order)= (From o In db.Orders Where o.ID = 2).ToList()
'  So long as Quantity is a property of order, we can sum it.
Dim sum = (Aggregate o In s Into Sum(o.Quantity))

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