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.net c# entity-framework many-to-many sql

Entity Framework many-to-many relationship include extremely slow

I have an Entity Framework 4 model, with 2 entities containing many-to-many relationship, so 3 tables, [Q], [P] and [Q2P]-cross table. Running code like:

context.Q.Include("P");

Results in long time wait (I waited like 5 mins then aborted it). Then I checked SQL generated and found this:

SELECT *
FROM ( SELECT *
FROM [Q] AS [Extent1]
LEFT OUTER JOIN (SELECT *, CASE WHEN ([Join1].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]
FROM [Q_P] AS [Extent2]
INNER JOIN [P] AS [Extent3] ON [Extent3].[Id] = [Extent2].[Id] ) AS [Join1] ON [Extent1].[Id] = [Join1].[Id]
) AS [Project1]
ORDER BY [Project1].[Id] ASC, [Project1].[C2] ASC

I can’t hide my suprise, WTF is this? The usual many-to-many SQL query

select * from [q2p]
join [q] on qId=q.Id
join [p] on pId=p.Id

executes in less than 1ms, while EF query executes forever.