Problems translating an SQL query to LINQ in VS Lightswitch - sql

Question

So, I am having an issue with an SQL query that is translated LINQ (and works - tested), but that same LINQ query does not work in Lightswitch. Of course I did not expect to work straight out, but I am struggling to properly convert it.
So here is a image of the tables that I base my query on:
http://dl.dropbox.com/u/46287356/tables.PNG
(sorry for outside link, but not enough rep points :))
The SQL query is the following:
SELECT WorkingUnits.Name AS WUName, ContractPositions.WUInstanceId,
Materials.Cost, BillingValues.Value, BillingValues.PricePerUnit
FROM WorkingUnits
INNER JOIN
Materials ON WorkingUnits.Id = Materials.Material_WorkingUnit
INNER JOIN ContractPositions ON
Materials.Id = ContractPositions.ContractPosition_Material
INNER JOIN BillingValues ON
ContractPositions.Id = BillingValues.BillingValue_ContractPosition
Now, I have transformed this to LINQ in the following way:
var query = from wu in this.DataWorkspace.ApplicationData.WorkingUnits
join m in this.DataWorkspace.ApplicationData.Materials on
new { Id = WorkingUnits.Id } equals new { Id = m.Material_WorkingUnit }
join cp in this.DataWorkspace.ApplicationData.ContractPositions on
new { Id = m.Id } equals new { Id = cp.ContractPosition_Material }
join bv in this.DataWorkspace.ApplicationData.BillingValues on
new { Id = cp.Id } equals new { Id = bv.BillingValue_ContractPosition }
select new
{
usage = bv.Value * bv.PricePerUnit,
totalCost = (bv.Value * bv.PricePerUnit) * m.Cost,
amount = (bv.Value*bv.PricePerUnit) * m.Cost / wu.WUPrice
};
Notice that I have changed a few things - like section of colums, as I do not need that in Lightswitch.
So while this works agains the SQL server, Lightswitch complains that I must consider explicitly specifying the type of the range variable 'WorkingUnits'.
I tried to cast it, but then there are other errors such as:
'int' does not contain a definition for 'Id' and no extension method 'Id'
accepting a first argument of type 'int' could be found (are you missing
a using directive or an assembly reference?)
So my questions is, how do I properly convert that query and expect it to work?
Also, If we take that my database is setup correctly, do I even need to use 'joins' in the LINQ?
Any ideas are appreciated!

Answer 1

try something like this
var query = from wu in this.DataWorkspace.ApplicationData.WorkingUnits
join m in this.DataWorkspace.ApplicationData.Materials on
wu.Id equals m.WorkingUnitID }
join cp in this.DataWorkspace.ApplicationData.ContractPositions on
m.Id equals cp.ContractPosition_Material
join bv in this.DataWorkspace.ApplicationData.BillingValues on
cp.Id equals bv.BillingValue_ContractPosition
select new
{
usage = bv.Value * bv.PricePerUnit,
totalCost = (bv.Value * bv.PricePerUnit) * m.Cost,
amount = (bv.Value*bv.PricePerUnit) * m.Cost / wu.WUPrice
};

Answer 2

What about starting at the bottom (BillingValues) and working your way up using the entity references?
eg
var query = from bv in this.DataWorkspace.ApplicationData.BillingValues
let m = bv.ContractPosition.Material
let wu = m.WorkingUnit
select new
{
usage = bv.Value * bv.PricePerUnit,
totalCost = (bv.Value * bv.PricePerUnit) * m.Cost,
amount = (bv.Value*bv.PricePerUnit) * m.Cost / wu.WUPrice
};