Dynamic LINQ and Dynamic Lambda expressions?

Question

What is the best way of dynamically writing LINQ queries and Lambda expressions?

I am thinking of applications where the end user can design business logic rules, which then must be executed.

I am sorry if this is a newbie question, but it would be great to get best practices out of experience.

Solution 1

I cannot recommend higher than you reading through the postings of Bart De Smet (http://community.bartdesmet.net/blogs/bart/), he is really brilliant when it comes to Lambda.

His recent series covered dynamic Lambda, starting with http://community.bartdesmet.net/blogs/bart/archive/2008/08/26/to-bind-or-not-to-bind-dynamic-expression-trees-part-0.aspx

Absolutely beautiful code.

Solution 2

Another possibility is to integrate a scripting runtime into your program, so that your users can write the business logic in a DSL. IronPython would be a candidate.

Solution 3

I can see two ways you can dynamically generate lambda's. You could try Reflection.Emit to generate IL (the .Net bytecode) directly and call them as a lambda or you can use the System.CodeDom and Microsoft.CSharp.CSharpCodeProvider to generate the code from higher level constructs. What you want to do depends on how you want the user to input this stuff. If you want the user to write C# then you can just use the built in compliler.

Generating Linq dynamically should be easier. You should be able to generate LINQ queries as expression trees in runtime and then pass them into an IQueryable to execute. I'd suggest you look into the documentation on IQueryable to learn more about this. Another way would be to pre-define a couple of linq queries and then allow the user to chain them together. This should be workable because any Linq query returns an IEnumerable that can be consumed by the next Linq query.

Comments

[aku]

I don't know "best-practices" for such things. I know how to solve concrete problem, but general "best way" is too vague matter.

[David Robbins]

Sound advice. We did that for configuration of workflows and it works quite nicely.

[D_Bye]

the only downside is that you may run into issues with full/partial trust that would prevent your code from executing in asp.net