LINQ: Building an IQueryable Provider - Part IX

Noticias externas — Thu, 17 Jan 2008 06:21:51 GMT

This is the nineth in a series of posts on how to build a LINQ IQueryable provider. If you have not read

LINQ: Building an IQueryable Provider - Part IX

LINQ in Action roller — Thu, 17 Jan 2008 08:21:02 GMT

This is the nineth in a series of posts on how to build a LINQ IQueryable provider. If you have not read

re: LINQ: Building an IQueryable Provider - Part IX

Frans Bouma — Thu, 17 Jan 2008 12:50:46 GMT

Interesting :)

I do this differently. I work with scopes. Scopes require a projection. For example the Join has two sides, both sides are individual scopes and thus require a projection. One can then decide when building the final query which ones to merge and which have to be wrapped into a derived table.

My system isn't reaching the end query you have, it has 1 derived table, as the end tree (which can't be merged further) contains a where node at the top with a select (and which thus markes a different scope) as source. The advantage is that it also doesn't need a lot of visitor calls to traverse the tree a lot of times, it can work with the information gathered up front. I use a preprocessor visitor to traverse the tree once to set all the scopes and aliases per scope.

I require this as our system works with relation objects, so when for example a join appears in the query, I have to create a relation object between the two sides to hand to our query API. At that point I have to reduce the trees on both sides and can't rely on post-processing with a visitor.

Btw, your query showed an error in my system, thanks for that :)

Following the logic of this query and the error I got (it assumed that a missing projection in the final node always suggested an entity fetch), I wrote this little query which gives wrong results on Linq to Sql (and mine)

var q = from c in db.Customers

join o in db.Orders on c.CustomerID equals o.CustomerID into co

select co;

As 'GroupJoin' is a nasty method to handle, the typical way to do that is to pick the left side and only pull the right side into the query if it's referenced. However 'co' is IEnumerable<Order>, but the query simply fetches all customers.

What's more is that the developer likely assumes that co is the joined list of customer and order.

Perhaps something to address in your next episode of this series :) Oh, and I think also a bit of information should be explained about 'Funcletization' (who cooked that up? ;)), which is a key element of a successful Linq provider (IMHO)

Community Convergence XXXIX

Charlie Calvert's Community Blog — Mon, 21 Jan 2008 09:42:11 GMT

Welcome to the XXXIX issue of Community Convergence. The big news this week is that Microsoft has begun

Community Convergence XXXIX

Charlie Calvert's Community Blog — Mon, 21 Jan 2008 09:43:44 GMT

Welcome to the XXXIX issue of Community Convergence. The big news this week is that Microsoft has begun

Community Convergence XXXIX

Charlie Calvert's Community Blog — Mon, 21 Jan 2008 09:45:37 GMT

Welcome to the XXXIX issue of Community Convergence. The big news this week is that Microsoft has begun

re: LINQ: Building an IQueryable Provider - Part IX

Fred — Fri, 01 Feb 2008 16:33:56 GMT

What's the license on the attached license?

re: LINQ: Building an IQueryable Provider - Part IX

Fred — Tue, 05 Feb 2008 11:23:43 GMT

What's the license on the attached *sample*? typo

re: LINQ: Building an IQueryable Provider - Part IX

Chris — Wed, 06 Feb 2008 20:28:44 GMT

Hi Matt,

Just wanted to say that this series is very useful for various projects I'm working on - looking forward to the next episode.

Thanks

Chris

Sesión "LINQ en profundidad” en TechDays 2008

Sobre C#, LINQ y algo más... — Fri, 22 Feb 2008 05:02:54 GMT

Un año más, Microsoft España ha tenido a bien confiarme la presentación sobre LINQ en su evento más importante

re: LINQ: Building an IQueryable Provider - Part IX

Marc Brooks — Fri, 07 Mar 2008 02:50:14 GMT

In the UnusedColumnRemover.VisitSelect, why can't you use your local columns value instead of repeatedly referencing the select.Columns property?

LINQ: Building an IQueryable Provider - Part X

The Wayward WebLog — Wed, 09 Jul 2008 02:33:47 GMT

This is the tenth in a series of posts on how to build a LINQ IQueryable provider. If you have not read the previous posts you'll want to find a nice shady tree, relax and meditate on why your world is so confused and full of meaningless tasks that it

Book Links

Programming Linq Book Log — Tue, 19 Aug 2008 20:23:59 GMT

Chapter Page Url 4 111 http://msdn2.microsoft.com/en-us/library/bb386907.aspx 4 111 http://msdn2.microsoft.com/en-us/library/bb399400.aspx

Building a LINQ IQueryable Provider - Part XII

The Wayward WebLog — Tue, 18 Nov 2008 04:06:17 GMT

This is the twelfth in a series of posts on how to build a LINQ IQueryable provider. If you have not

LINQ links

The Wayward WebLog — Tue, 18 Nov 2008 20:27:29 GMT

Part I - Reusable IQueryable base classes Part II - Where and reusable Expression tree visitor Part II

LINQ: Building an IQueryable provider series

Floating Heart — Thu, 19 Mar 2009 17:52:26 GMT

http://blogs.msdn.com/mattwar/pages/linq-links.aspx Here's a list of all the posts in the building