Why does Linq to Entities generate Left Outer Joins?

Question

I was wondering if anyone knew why linq to entities always seems to generate left outer joins. I would understand it on an optional relationship but it doesn't make good sense when the relationship is mandatory.

Does anyone have any idea how to make it generate inner joins instead?

Answer 1

http://blogs.microsoft.co.il/blogs/idof/archive/2008/10/01/entity-framework-generated-queries-look-out.aspx

Answer 2

You can create inner joins. You simply need to use the join keyword. For example, here is a query against the AdventureWorks database:

var query = from od in db.SalesOrderHeader
            join c in db.Customer on od.Customer.CustomerID equals c.CustomerID
            select new { c.AccountNumber, od.OrderDate };

The equivalent SQL:

Select C.AccountNumber, OD.OrderDate 
From Sales.SalesOrderHeader As OD
    Join Sales.Customer As C
        On C.CustomerID = OD.CustomerID

And here is the SQL that the LINQ query produced:

SELECT 
1 AS [C1], 
[Extent2].[AccountNumber] AS [AccountNumber], 
[Extent1].[SalesOrderID] AS [SalesOrderID], 
[Extent1].[RevisionNumber] AS [RevisionNumber], 
[Extent1].[OrderDate] AS [OrderDate], 
[Extent1].[DueDate] AS [DueDate], 
[Extent1].[ShipDate] AS [ShipDate], 
[Extent1].[Status] AS [Status], 
[Extent1].[OnlineOrderFlag] AS [OnlineOrderFlag], 
[Extent1].[SalesOrderNumber] AS [SalesOrderNumber], 
[Extent1].[PurchaseOrderNumber] AS [PurchaseOrderNumber], 
[Extent1].[AccountNumber] AS [AccountNumber1], 
[Extent1].[CreditCardApprovalCode] AS [CreditCardApprovalCode], 
[Extent1].[SubTotal] AS [SubTotal], 
[Extent1].[TaxAmt] AS [TaxAmt], 
[Extent1].[Freight] AS [Freight], 
[Extent1].[TotalDue] AS [TotalDue], 
[Extent1].[Comment] AS [Comment], 
[Extent1].[rowguid] AS [rowguid], 
[Extent1].[ModifiedDate] AS [ModifiedDate], 
[Extent1].[BillToAddressID] AS [BillToAddressID], 
[Extent1].[ContactID] AS [ContactID], 
[Extent1].[ShipMethodID] AS [ShipMethodID], 
[Extent1].[CreditCardID] AS [CreditCardID], 
[Extent1].[CurrencyRateID] AS [CurrencyRateID], 
[Extent1].[CustomerID] AS [CustomerID], 
[Extent1].[SalesPersonID] AS [SalesPersonID], 
[Extent1].[TerritoryID] AS [TerritoryID]
FROM  [Sales].[SalesOrderHeader] AS [Extent1]
INNER JOIN [Sales].[Customer] AS [Extent2] ON ([Extent1].[CustomerID] = [Extent2].[CustomerID]) OR (([Extent1].[CustomerID] IS NULL) AND ([Extent2].[CustomerID] IS NULL))