Comments on: PrefetchPaths in Depth

By: jhelles

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By: David Elizondo

David Elizondo — Wed, 27 Jan 2010 21:20:30 +0000

@Neil, If you want to filter on the root (for instance, filter the order), simply use the “where” clause on the main linq query. If you want to filter on the prefetchpath (for instance, filter the orderDetails of the order) you should use the “.Where” of the PathEdge. See the http://www.llblgening.com/archive/2009/10/prefetchpaths-in-depth/#filteringandsorting code snippet for lamdas.

By: Neil Burnett

Neil Burnett — Tue, 26 Jan 2010 21:34:32 +0000

Thanks for the article. I wonder if you could add a Linq with Lamda expressions example to the common mistake “Filter on PrefetchPath expecting to filter on the root”? I have been trying for a while but can’t get it right. Thanks.

By: David Elizondo

David Elizondo — Fri, 20 Nov 2009 23:31:44 +0000

@Sebastian. If you know upfront the number of levels that you want to prefetch, you can specify a prefetchPath with SubPaths to the number of levels you want. If you don’t, that’s no possible, it’s wise you to return first the n levels you want. If you cant, the best option I can think is use a stored procedure that perform a recursive query and return results, then in your code you can use projections to project the results into LLBLGen entities.

By: SebastiÃ¡n Carrozzo

SebastiÃ¡n Carrozzo — Fri, 20 Nov 2009 18:42:00 +0000

Excelent article. I didnÂ´t know of the prefetch subpath…

Do you know of a way to do recursive prefetchs?

LetÂ´s suppose thereÂ´s a tabla Person with PersonID with a recursive relation using ParentID as itÂ´s own FK. What I would like to do is to get a Person and get itÂ´s father and itÂ´s grandfather and also his great grandfather and so.

I know I could add a prefetch path to the Person to get his father and a subpath to get his grandfather, but the idea is that I donÂ´t know the depth of the recursive paths.

By: David Elizondo

David Elizondo — Fri, 16 Oct 2009 00:05:15 +0000

@Alex. Indeed, I forgot to mention that as those are edge cases. Anyway, these are some scenarios where you could have troubles:

Trailing spaces: http://llblgen.com/tinyforum/Messages.aspx?ThreadID=9941
CaseSensitiveCollation: http://llblgen.com/tinyforum/Messages.aspx?ThreadID=14574

I linked the threads with the solution.

By: Alex Walker

Alex Walker — Thu, 15 Oct 2009 21:56:08 +0000

Have you ever seen a case where some entities that are being prefetched are not included, but some are?

By: Andrea

Andrea — Thu, 15 Oct 2009 03:00:48 +0000

Congrats on the great effort! You are doing a great job indeed! ;o)