Linq queries in Entity Framework 4. Horrible performance

In my project I'm using EntityFramework 4 for working with data. I found horrible performance problems with a simple query. When I looked at the profiler on a sql query, generated by EF4, I was shocked.

I have some tables in my entity data model:

It looks pretty simple. I'm trying to select all product items from specified category with all related navigation properties.

I wrote this LINQ query:

ObjectSet<ProductItem> objectSet = ...; 
int categoryId = ...; 

var res = from pi in objectSet.Include("Product").Include("Inventory").Include("Inventory.Storage") 
where pi.Product.CategoryId == categoryId 
select pi;

EF generated this sql query:

SELECT   [Project1].[pintId1]          AS [pintId], 
[Project1].[pintId]           AS [pintId1], 
[Project1].[intProductId]     AS [intProductId], 
[Project1].[nvcSupplier]      AS [nvcSupplier], 
[Project1].[ nvcArticle]      AS [ nvcArticle], 
[Project1].[nvcBarcode]       AS [nvcBarcode], 
[Project1].[bIsActive]        AS [bIsActive], 
[Project1].[dtDeleted]        AS [dtDeleted], 
[Project1].[pintId2]          AS [pintId2], 
[Project1].[nvcName]          AS [nvcName], 
[Project1].[intCategoryId]    AS [intCategoryId], 
[Project1].[ncProductType]    AS [ncProductType], 
[Project1].[C1]               AS [C1], 
[Project1].[pintId3]          AS [pintId3], 
[Project1].[intProductItemId] AS [intProductItemId], 
[Project1].[intStorageId]     AS [intStorageId], 
[Project1].[dAmount]          AS [dAmount], 
[Project1].[mPrice]           AS [mPrice], 
[Project1].[dtModified]       AS [dtModified], 
[Project1].[pintId4]          AS [pintId4], 
[Project1].[nvcName1]         AS [nvcName1], 
[Project1].[bIsDefault]       AS [bIsDefault] 
FROM     (SELECT [Extent1].[pintId]         AS [pintId], 
[Extent1].[intProductId]   AS [intProductId], 
[Extent1].[nvcSupplier]    AS [nvcSupplier], 
[Exte