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Dynamic Lambda expression inside an expression query

Can a dynamic Linq expression be used inside a query expression? Something like that:

from obj1 in ObjectSet1
let res = ObjectSet2.Where(* SomeExpression *)
where ...
select ...

I am trying to build an expression Expression.Lambda<Func<TSource, bool>>

for SomeExpression.

  • Is it possible to use a dynamic Linq expression in an expression query or do I need to rebuild the entire expression tree from scratch?
  • How can I, if any, use obj1 when creating SomeExpression?

Note. I am using Entity Framework, I cannot use SomeExpression.Compile () on Expression Tree.

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2 answers


Not only is this possible, it is normal. Large expression trees can be generated from smaller trees (this is what LINQ does). You only need to transfer Expression<Func<TSource, bool>>

to Where()

.



You can see how in my answer to this other thread here - replace the operator in the Where Lambda section with a parameter . The interesting part is in the method MakeWhereLambda

.

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If you want it to be fully dynamic, one possible option would be to use serialization serialization:

http://expressiontree.codeplex.com/

I started using this a while ago, but this task has been refocused, so I'm not sure how appropriate it is for any given task. However, it looks pretty good ...



Hope it helps.

Nat

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