Question

I have a Linq expression that (for northwind) gets the total qty ordered per product for customer id ‘ALFKI’

from od in db.OrderDetails
    where od.Order.CustomerID == "ALFKI"
    group od by od.Product.ProductName into g1
    select new { ProductName = g1.Key, Total = g1.Sum(od => od.Quantity) }

This is fine but to fully understand Linq, I want to try and formulate the expression in a world where Linq2Sql doesn’t nicely build the property bridges through foreign keys.

For instance, in the above expression, I’m accessing od.Order.CustomerID. I want to assume that od.OrderID is as far as I can go.

Looking at the SQL for the expression, I have:

SELECT SUM(CONVERT(Int,[t0].[Quantity])) AS [Total], [t2].[ProductName]
FROM [Order Details] AS [t0]
INNER JOIN [Orders] AS [t1] ON [t1].[OrderID] = [t0].[OrderID]
INNER JOIN [Products] AS [t2] ON [t2].[ProductID] = [t0].[ProductID]
WHERE [t1].[CustomerID] = @p0
GROUP BY [t2].[ProductName] 

This is as far as I’ve managed to get:

from od in db.OrderDetails
    join o in db.Orders on od.OrderID equals o.OrderID
    join p in db.Products on od.ProductID equals p.ProductID
    where o.CustomerID == "ALFKI"
    group od by od.ProductID into g1
    select new { ProductName = g1.Key, Total = g1.Sum(od => od.Quantity) }

This is almost there but g1.Key is referring to the ProductID. I can’t seem to get at the ProductName and the order quantity at the same time.

Thanks

Answer 1

Try creating a new anonymous type for your group by:

from od in db.OrderDetails
    join o in db.Orders on od.OrderID equals o.OrderID
    join p in db.Products on od.ProductID equals p.ProductID
where o.CustomerID == "ALFKI"
group od by new { p.ProductID, p.ProductName } into g1
select new { 
    ProductName = g1.Key.ProductName, 
    Total = g1.Sum(od => od.Quantity) }