LINQ: Building an IQueryable provider - Part VII

Noticias externas — Wed, 05 Sep 2007 03:48:36 GMT

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

LINQ: Building an IQueryable provider - Part VII

Roller — Wed, 05 Sep 2007 04:34:39 GMT

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

re: LINQ: Building an IQueryable provider - Part VII

Frans Bouma — Wed, 05 Sep 2007 10:54:27 GMT

And now if the target db doesn't support 'cross apply' ? Is it then even possible to produce valid SQL, or better: is it possible to interpret the expression tree in all cases with 2 or more froms so valid SQL is produced for that DB?

I also fail to see why there's no left/right keyword. I mean: (think northwind), what if I want all employees who haven't filed any orders yet. This is a simple left join with a NULL test predicate in the where, however hard to formulate in Linq. I really wonder why it's so hard to formulate, I don't really see a reason to make it this complicated simply because it's a well known query construct in SQL and Linq is a new language. Not designing it in (but via a workaround with DefaultIfEmpty() which leads to painful interpretation routines in the linq provider) is IMHO a flaw.

re: LINQ: Building an IQueryable provider - Part VII

mattwar — Wed, 05 Sep 2007 17:22:19 GMT

Frans, in most cases it is possible to convert a cross apply into a cross join, but the transformation is very involved and so not something I would dive into at this point in the series (I don't have enough support built up in my tree manipulating toolbox yet.)

There are a few cases where the cross apply cannot be converted. For example, use of TOP or aggregates on the right-hand side whose scoping depends on the left-hand side variable.

re: LINQ: Building an IQueryable provider - Part VII

Frans Bouma — Wed, 05 Sep 2007 19:33:07 GMT

Ok, so this will be a real challenge for providers which support other databases than just sqlserver?

Also how to perform the left join filter example I posted?

Say I want all customers who don't have an order (in my northwind db, that's 2). if I do:

var q = from c in nw.Customers

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

from o in co.DefaultIfEmpty()

where o != null

select c;

I don't get the right results. (all order rows joined with the customers) But all examples I see on the net about left joins are about fetching customer data AND order data, but I'm only interested in customer data which doesn't have order data. No matter how long I stare at this, I can't find a way to get the query I want.

It's not that I'm looking for corner cases in where Linq fails, (not linq to sql, but the language Linq), I'm looking for ways how normal constructs are done in Linq and if these aren't possible, why they aren't possible, or done in a cumbersome way (like the long complex route with cross apply, which is likely not supported in a large range of databases other than sqlserver).

re: LINQ: Building an IQueryable provider - Part VII

Frans Bouma — Wed, 05 Sep 2007 19:36:21 GMT

Never mind my previous post. This query works:

var q = from c in nw.Customers

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

from o in co.DefaultIfEmpty()

where o == null

select c;

which gives an odd query with a 'test' field. This query:

var q = from c in nw.Customers

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

from o in co.DefaultIfEmpty()

where o.OrderID == null

select c;

gives a more natural query.

re: LINQ: Building an IQueryable provider - Part VII

rogerj — Sat, 08 Sep 2007 03:20:24 GMT

Pingback from http://oakleafblog.blogspot.com/2007/09/linq-and-entity-framework-updates-for.html.

Community Convergence XXXI

Charlie Calvert's Community Blog — Wed, 26 Sep 2007 03:38:52 GMT

Welcome to the thirty-first edition of Community Convergence. This issue features links to seven very

Community Convergence XXXI

Charlie Calvert's Community Blog — Wed, 26 Sep 2007 03:43:21 GMT

Welcome to the thirty-first edition of Community Convergence. This issue features links to seven very

LINQ: Building an IQueryable Provider - Part VIII

The Wayward WebLog — Wed, 10 Oct 2007 00:49:29 GMT

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

LINQ: Building an IQueryable Provider - Part VIII

The Wayward WebLog — Wed, 10 Oct 2007 00:55:19 GMT

Implementing OrderBy Today's topic is translating those order-by clauses. Fortunately, there is only one way to do ordering, and that's using the LINQ ordering specific query operators. The bad news is that there are four different operators.

TerraServer Sample: A LINQ Provider

Charlie Calvert's Community Blog — Mon, 07 Jan 2008 04:34:59 GMT

Over the holidays Alex Turner, Mary Deyo and I added a new sample to the downloadable version of the

TerraServer Sample: A LINQ Provider

Charlie Calvert's Community Blog — Mon, 07 Jan 2008 04:37:05 GMT

Over the holidays Alex Turner, Mary Deyo and I added a new sample to the downloadable version of the

LINQ: Building an IQueryable Provider - Part IX

The Wayward WebLog — Thu, 17 Jan 2008 06:06:23 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

The Wayward WebLog — Thu, 17 Jan 2008 06:08:10 GMT

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

LINQ Tips: Implementing IQueryable Provider

Shahed Khan (MVP C#) — Thu, 07 Feb 2008 08:49:34 GMT

Check out the following from Matt Warrens blog posts, if you are interested on how to implement IQueryable...

LINQ Tips: Implementing IQueryable Provider

Shahed Khan (MVP C#) — Thu, 07 Feb 2008 08:49:57 GMT

Check out the following from Matt Warrens blog posts, if you are interested on how to implement IQueryable

LINQ: Building an IQueryable Provider - Part X

The Wayward WebLog — Wed, 09 Jul 2008 02:29:26 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

LINQ: Building an IQueryable Provider - Part XI

The Wayward WebLog — Mon, 14 Jul 2008 22:32:05 GMT

This is the eleventh 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 do so before proceeding, or at least before proceeding to copy the code into your own project and telling your

Building a LINQ IQueryable Provider - Part XII

The Wayward WebLog — Tue, 18 Nov 2008 04:04:44 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 20:26:45 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 17:51:22 GMT

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