LINQ, Take Two: Realizing the LINQ to Everything Dream
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Bio
Bart De Smet is a Software Development Engineer on the Cloud Programmability team, an avid blogger and a popular speaker on various international conferences. In his current role, he’s actively involved in the design and implementation of Reactive Extensions for .NET (Rx) and on an extended “LINQ to Anything” mission.
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Ajay Bhosale
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It doesn't have to be IQueryable
by
Stefan Wenig
However, beyond the simple scenarios he shows there's little chance to get there. Take an O/R mapper, the most common scenario for LINQ providers. When we want to use our POCO classes for queries, we're out of luck here. Even if our query factory returns a MyQueryable<MyType> that does not implement IQueryable<MyType>, MyType will likely have members that implement IEnumerable<T>, and now any LINQ expression using these members will be compiled. Unsupported features will just break at runtime, and there's nothing you can do about it.
The consequence is that any useful LINQ provider needs to implement almost anything, or it will be useless because nobody wants to guess what's possible and then try it out and re-write it until it works. A complete LINQ provider is much harder to write than one that supports, say, 80% of query features. And there's alyways stuff that can _only_ be executed in memory (basically any user-defined method, comparers etc.)
We spent some time figuring out how we could add compile-time limitations to LINQ provider toolkit (relinq.codeplex.com), but it just doesn't work without generating specific queryable classes for any classes participating in queries. Which in turn would not only mess up the build process, but also create circular dependencies whenever you want to write a LINQ query in a queryable class.</t></mytype></mytype>
Re: It doesn't have to be IQueryable
by
Stefan Wenig
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