Write a LINQ query for total sales of each salesman according product category - linq-to-sql

Question

I'm trying to write a LINQ query to find number of total sales made by each employee, according product categories using Northwind database.
Required result should be like:
EmployeeID : ProductCategoryID : totalNumberofSales
for example:
1stEmployee : 1st category : x sales
.
.
.
nthEmployee : nthCategory : y sales
Tables from NorthWind database are EMPLOYEES, ORDERS, ORDER_DETAILS, PRODUCTS, CATEGORIES.
I tried it this, but stuck at the end.
List<ORDER_DETAILS> o_details = db.ORDER_DETAILS.ToList();
List<ORDERS> orders = db.ORDERS.ToList();
List<CATEGORIES> categories = db.CATEGORIES.ToList();
List<EMPLOYEES> employee = db.EMPLOYEES.ToList();
List<PRODUCTS> products= db.PRODUCTS.ToList();
var list= orders.GroupJoin(employee, o => o.PersonelID, e => e.PersonelID, (e, os) => new { e, os.})
.GroupJoin(o_details, tp => tp.e.OrderID, od => od.OrderID, (od, tps) => new { od, tps })
.GroupJoin(products, tp2 => tp2.od.e.ORDER_DETAILS, p => p.ORDER_DETAILS, (tp2,ps) => new{tp2, ps})
.GroupJoin(categories, tp3=>tp3.ps, c=>c.CategoryID, (tp3s,cs)=>new { tp3s, cs}).GroupBy(m => new { }

Answer 1

Your Northwind database may be different from mine as I don't have a PersonelID column, but have a EmployeeID, but hopefully this will help.
If it wasn't for the discount, then could be a simple matter of grouping the orderDetails records, ie
var summary = (from od in OrderDetails
group od by new { od.Order.EmployeeID, od.Product.CategoryID } into results
orderby results.Key.EmployeeID, results.Key.CategoryID
select new
{
results.Key.EmployeeID,
results.Key.CategoryID,
Sales = results.Sum(a => a.UnitPrice * a.Quantity)
}
).ToList();
The discount makes it more complicated because of rounding issues etc, but you can use the OrderDetailsExtended view which provides the ExtendedPrice column, but means you need to perform explicit joins rather than navigation properties, eg
var summary2 = (from od in OrderDetailsExtended
join order in Orders on od.OrderID equals order.OrderID
join product in Products on od.ProductID equals product.ProductID
group od by new { order.EmployeeID, product.CategoryID } into results
orderby results.Key.EmployeeID, results.Key.CategoryID
select new
{
results.Key.EmployeeID,
results.Key.CategoryID,
Sales = results.Sum(a => a.ExtendedPrice)
}
).ToList();