multiple grouping, inner joning in Linq - linq

Question

I am trying to translate this into Linq and cannot figure it out:
SELECT
CustomerOrder.ShipState, MONTH(OrderFulfillment.OrderDate) AS Mnth,
YEAR(OrderFulfillment.OrderDate) AS Yer,
SUM(OrderFulfillment.Tax) AS TotalTax
FROM
OrderFulfillment INNER JOIN
CustomerOrder ONOrderFulfillment.OrderID =CustomerOrder.OrderID
WHERE
(OrderFulfillment.Tax > 0)
GROUP BY
CustomerOrder.ShipState, MONTH(OrderFulfillment.OrderDate),
YEAR(OrderFulfillment.OrderDate)
ORDER BY
YEAR(OrderFulfillment.OrderDate) DESC, CustomerOrder.ShipState,
MONTH(OrderFulfillment.OrderDate) DESC
I have Linqpad and have gone through a bunch of the examples but cannot figure this out.

Answer 1

I think you want to do something like this:
from c in CustomerOrder
join o in OrderFulfillment on c.OrderId equals o.OrderId
where
o.Tax > 0
group o by
new { c.ShipState, Mnth = of.OrderDate.Month, Yer = of.OrderDate.Year }
into g
orderby
g.Key.Yer descending, g.ShipState, g.Key.Mnth descending
select
new { g.Key.ShipState, g.Key.Mnth, g.Key.Yer,
TotalTax = g.Sum(i => i.Tax) };
I haven't tried to compile it, but I think this is something along the lines of what you want.
The idea is that first you perform your join to link the customers and orders. Then apply your filter condition.
At that point, you want to get all the orders that have a particular group, so the group operator is applied.
Finally, order the results, then select out all info from the keys for each group, and sum up the tax in each of the group.

Answer 2

First of all, it would be nice to know what exactly you can't figure out. If you're completely lost and don't know where to begin then you need to google around for linq joining and grouping.
Here's something I did recently that may (possibly) point you in the right direction:
// This groups items by category and lists all category ids and names
from ct in Categories
join cst in Category_Subtypes
on ct.Category_Id equals cst.Category_Id
join st in Subtypes
on cst.Subtype_Id equals st.Subtype_Id
where
st.Type_Id == new Guid(id)
group ct by new { ct.Category_Id, ct.Display_Text } into ctg
select new
{
Id = ctg.Key.Category_Id,
Name = ctg.Key.Display_Text
}