LightSwitch Linq To Entities query problem !

I'm very new to Linq and Entities Framework. I'm trying to create a WCF RIA Service into a LightSwitch Orders Management application I'm creating. I've already created 7 or 8 queries using Linq (with lot of headaches) but I succeded. Now I need to create a query who gets TotalSales and TotalExpenses by month by using three tables :

DetailsVentes (SaleDetails) composed of : DateOfOrder, Quantity, UnitPrice, Total.... etc DetailsAchat (PurchaseDetails) composed of the same fields Charges (Expenses) composed of : DateOfExpense, ExpenseType, Cost....etc

Now I want to have a query that finds the Net Income per month (income=TotalSales-TotalPurchases-TotalExpenses)

I tried this query

      Return From od In Me.Context.DetailsVentes
                From od2 In Me.Context.DetailsAchats
                   From od3 In Me.Context.Charges
              Group By Month = od.Vente.DateCommande.Month, Year = od.Vente.DateCommande.Year
              Into g = Group
              Select New TCR With {.Mo开发者_如何学JAVAnth = Month, .Year = Year, 
.MonthYearString = Month & "/" & Year, 
.TotalVentes = g.Sum(Function(s) (s.od.PrixUnitaire * s.od.Quantité)), 
.TotalAchats = g.Sum(Function(s) (s.od2.PrixAchat * s.od2.Quantité)), 
.TotalCharges = g.Sum(Function(s) (s.od3.Cout))}

Where Vente is Sale (Order) and DetailVentes is OrderDetails Achat is Purchase, and DetailAchat PurchaseDetail a Charge is an Expense.

The Problem is I got weird results. All values (TotalVentes, TotalAchats, TotalCharges) are multiplicated by 13 !

For eg if I have 10 000 USD totalSales for June 2011, this query returns 130 000 USD !

I'm really stuck 4 days trying to get the correct query.

I repeat I'm new to Linq :p

Thank you very much.

Edit : I tried @Jason advice I did this :

Return From c In Me.Context.Charges
                         Join v In Me.Context.DetailsVentes On c.DateCharge.Month Equals v.Vente.DateCommande.Month And c.DateCharge.Year Equals v.Vente.DateCommande.Year
                 Join a In Me.Context.DetailsAchats On c.DateCharge.Month Equals a.Achat.DateCommande.Month And c.DateCharge.Year Equals a.Achat.DateCommande.Year
 Group By month = c.DateCharge.Month, Year = c.DateCharge.Year
                 Into g = Group
Select New TCR With {.Month = month, .Year = Year, .MonthYearString = "", .TotalAchats = g.Sum(Function(c) (c.a.Quantité * c.a.PrixAchat)), .TotalCharges = 45000, .TotalVentes = 250000, .TCRSingle = 0}

And results are still very weird (very high) ! Any exemple I can follow ??

Thank you.

I finally had it works by splitting the query to 3 queries like this :

Dim vt = From od In Me.Context.DetailsVentes
     Group By Month = od.Vente.DateCommande.Month, Year = od.Vente.DateCommande.Year
     Into g = Group
     Select New VentesParMois With {.Month = Month, .Year = Year,
                                   .TotalVentesSingle = g.Sum(Function(od) _
                                       (od.PrixUnitaire * od.Quantité))}



Dim at = From od In Me.Context.DetailsAchats
      Group By Month = od.Achat.DateCommande.Month, Year = od.Achat.DateCommande.Year
      Into g = Group
      Select New AchatsParMois With {.Month = Month, .Year = Year, 
                                    .TotalAchatsSingle = g.Sum(Function(od) _
                                        (od.PrixAchat * od.Quantité))}


Dim ct = From od In Me.Context.Charges
     Group By Month = od.DateCharge.Month, Year = od.DateCharge.Year
     Into g = Group
     Select New ChargesParMois With {.Month = Month, .Year = Year, 
                                   .TotalChargesSingle = g.Sum(Function(od) _
                                       (od.Montant))}



Dim q = From a In at.AsEnumerable, v In vt.AsEnumerable, c In ct.AsEnumerable
        Where a.MonthYear = v.MonthYear AndAlso a.MonthYear = c.MonthYear
                Select New TCR With {.Month = a.Month, .Year = a.Year, .TotalAchats = a.TotalAchats, .TotalVentes = v.TotalVentes, .TotalCharges = c.TotalCharges}


Return q.AsQueryable

Thank you very much Jason.

I suspect you want a join somewhere in your query rather than a cartesian product (a join without any join conditions).