Third-Party LINQ Providers

Following is a short list of the third-party LINQ providers I've found to date in more-or-less chronological order:

• LINQ to WebQueries by Hartmut Maennel handles searches in the SiteSeer and MSDN Web sites. (This provider predates Fabrice's LINQ to Amazon provider by a few days.)
• LINQ to Amazon by Fabrice Marguerie, a co-author of the forthcoming LINQ in Action book, was the first third-party LINQ provider that I know of. LINQ to Amazon returns lists of books meeting specific criteria.
• LINQ to RDF Files by Hartmut Maennel handles queries against Resource Description Format files' triples. Part I of the two-part post is here.
• LINQ to MySQL by George Moudry, based on the LINQ May 2006 CTP, was in the development stage as of January 2007, but George says it's "capable of simplest queries and updates" and "now has support for most primitive joins."
• LINQ to NHibernate by Ayende Rahien (a.k.a. Oren Eini) translates LINQ queries to NHibernate Criteria Queries and is based on the Orcas March 2007 CTP. The documentation that describes development of the provider presently is at the Part 1 stage.
• LINQ to LDAP by Bart de Smet is a "query provider for LINQ that's capable of talking to Active Directory (and other LDAP data sources potentially) over LDAP." As of 4/11/2007, Bart's "IQueryable Tales - LINQ to LDAP" consisted of Part 0: Introduction, Part 1: Key Concepts, Part 2: Getting Started with IQueryable, Part 3: Why do we need entities?, Part 4: Parsing and executing queries, and Part 5: Supporting Updates.
• LINQ to Flickr by Mohammed Hossam El-Din (Bashmohandes) uses the open-source FlickrNet C# library as its infrastructure.
• LINQ to Google Desktop by Costa Rican programming language enthusiast Luis Diego Fallas supports GDFileResult and GDEmail types. A subsequent Adding support for projections to Linq to Google Desktop implements the LINQ Select expression.
• LINQ to SharePoint by Bart de Smet supports writing LINQ queries for SharePoint lists in both C# 3.0 and Visual Basic 9.0 and communicates with SharePoint via Web services or though the SharePoint Object Model. The SpMetal command-line utility automates C# or VB class generation.
• LINQ to Streams (SLinq, Streaming LINQ) by Oren Novotny processes continuous data streams, such as stock tickers or sensor data. The project's home page on CodePlex includes an animated GIF simulation of a stock ticker displayed in a DataGridView. The current version supports Select, Where, Order By, and Descending only.
• LINQ to Expressions (MetaLinq) by Aaron Erickson (the developer of Indexes for Objects a.k.a i4o*) lets you query over and edit expression trees with LINQ. Like .NET strings, LINQ expression trees are immutable; the only way you can change a LINQ expression tree is to make a copy, modify the copy, and then replace the original. MetaLinq's ExpressionBuilder lets you create an "Editable Shadow of an expression tree, modify it in place, and then by calling ToExpression on the shadow tree, generate a new, normal, immutable tree." ExpressionBuilder is an analog of the .NET StringBuilder.

* i4o isn't a LINQ provider, per se, but a helper class that can increase the speed of LINQ queries against large collections by a factor of 1,000 or more. InfoQ published on June 22, 2007, Aaron Erickson on LINQ and i4o, an interview of Aaron Erickson by Jonathan Allen about i4o's purpose and background.

Ayende observes:

There is an appalling lack of documentation about how to implement LINQ providers. ... I decided to document what I found out while building LINQ for NHibernate.

However, the "appalling lack of documentation" hasn't thwarted the work of third-party LINQ providers for specialty data domains. A search of the CodePlex site on LINQ returned 15 projects as of 6/3/2007.

If you know of other third-party LINQ providers in development, please leave a comment.

Thanks in advance.

Update 3/29/2007: .NET Rocks features "Oren Eini On NHibernate and RhinoMocks!" as its 3/29/2007 broadcast. LINQ to NHibernate might become a much more popular LINQ provider if the ADO.NET Team doesn't finish the EDM Designer by Orcas RTM. The interview with Oren starts at 11:00. (Thanks to Danny Simmons for the heads-up.) .NET Rocks TV (dnrTV) taped an instructional video interview with Oren on January 25, 2007.

Update 4/7/2007: Added Bart de Smet's LINQ to LDAP project, which includes extensive IL code inspection of LINQ queries.

Bobby Diaz has extended Ayende's initial Part 1 From ... In ... Where ... Select implementation with Part 2: Ordering and Paging (adds Order By, Then By, OrderByDescending, ThenByDescending, Take, Skip, and Distinct) and Part 3: Aggregate and Element Operators (adds First, FirstOrDefault, Single, SingleOrDefault, Average, Count, LongCount, Max, Min, and Sum.) The momentum is building behind LINQ to NHibernate.

Update 4/11/2007: Added Mohammed Hossam El-Din's LINQ to Flickr provider and updated LINQ to LDAP with parts 4 and 5.

Update 5/6/2007: Added Bart de Smet's LINQ to SharePoint project, version 0.1.2.0 Alpha release.

Update 5/12/2007: Added Helmut Maennel's early LINQ to WebSearch and LINQ to RDF Files providers. I haven't tested these providers with later LINQ implementations.

Update 6/3/2007: Added Oren Novotny's LINQ to Streams (SLinq) and Aaron Erickson's LINQ to Expressions (MetaLinq) and Indexes for Objects (i4o).

Update 6/11/2007: Added Luis Diego Fallas' LINQ to Google Desktop of May 11 and 12, 2007, which I had missed.

Update 7/22/2007: Added link to inteview with Aaron Erickson about i4o.

Update 8/7/2007: Aaaron Erickson has written "Indexed LINQ" for .NET Developer's Journal. Subtitiled "Optimizing the performance of LINQ queries using in-memory indexes," the article covers the theory behind creating indexes on in-memory collections and applying an extension method to the Where() standard query operator to enable speeding queries by up to a factor of 100 or so with the indexes. You can download the source code, runtime binary or both for i4o at http://www.codeplex.com/i4o.

Technorati tags: LINQ, Orcas March 2007 CTP, Orcas, NHibernate