Question

Can anyone explain why join by entity rather than id generates some really ugly sql when actually conceptually its doing what you’d think was the same thing? e.g.

By id

from companyDirector in CompanyDirectors
join contactAddress in ContactAddresses
  on companyDirector.ContactAddress.Id equals contactAddress.Id
select new {companyDirector, contactAddress}

Generates

FROM  [COMPANY] AS [Extent1]
    INNER JOIN [ADDRESS] AS [Extent2] ON [Extent1].[CONTACT_ADDRESS_ID] = [Extent2].[CONTACT_ADDRESS_ID]

By instance

from companyDirector in CompanyDirectors
join contactAddress in ContactAddresses
  on companyDirector.ContactAddress equals contactAddress
select new {companyDirector, contactAddress}

generates

FROM  [COMPANY] AS [Extent1]
INNER JOIN [ADDRESS] AS [Extent2] ON  EXISTS (SELECT 
    1 AS [C1]
    FROM    ( SELECT 1 AS X ) AS [SingleRowTable1]
    LEFT OUTER JOIN  (SELECT 
        [Extent3].[CONTACT_ADDRESS_ID] AS [CONTACT_ADDRESS_ID]
        FROM [ADDRESS] AS [Extent3]
        WHERE [Extent1].[CONTACT_ADDRESS_ID] = [Extent3].[CONTACT_ADDRESS_ID] ) AS [Project1] ON 1 = 1
    LEFT OUTER JOIN  (SELECT 
        [Extent4].[CONTACT_ADDRESS_ID] AS [CONTACT_ADDRESS_ID]
        FROM [ADDRESS] AS [Extent4]
        WHERE [Extent1].[CONTACT_ADDRESS_ID] = [Extent4].[CONTACT_ADDRESS_ID] ) AS [Project2] ON 1 = 1
    WHERE [Project1].[CONTACT_ADDRESS_ID] = [Extent2].[CONTACT_ADDRESS_ID]
)

That looks pretty inefficient to me, forcing you into the id route. Why is it doing the left join twice, never mind once??

Answer 1

In the end, for me EF still lacks the maturity and features required to perform in the big wide world. So I dropped it in favour of NHibernate which generates simply beautiful and optimised SQL.