Lambda to Expression tree conversion

Question

I will keep it really simple,

How do I get expression tree out of lambda??

or from query expression ?

Answer 1

Just to expand on Konrad's answer, and to correct Pierre, you can still generate an Expression from an IL-compiled lambda, though it's not terribly elegant. Augmenting Konrad's example:

// Gives you a lambda:
Func<int, int> f = x => x * 2;

// Gives you an expression tree:
Expression<Func<int, int>> g = x => f(x);

Answer 2

Konrad's reply is exact. You need to assign the lambda expression to Expression<Func<...>> in order for the compiler to generate the expression tree. If you get a lambda as a Func<...>, Action<...> or other delegate type, all you have is a bunch of IL instructions.

If you really need to be able to convert an IL-compiled lambda back into an expression tree, you'd have to decompile it (e.g. do what Lutz Roeder's Reflector tool does). I'd suggest having a look at the Cecil library, which provides advanced IL manipulation support and could save you quite some time.

Answer 3

You must assign the lambda to a different type:

// Gives you a delegate:
Func<int, int> f = x => x * 2;
// Gives you an expression tree:
Expression<Func<int, int>> g = x => x * 2;

The same goes for method arguments. However, once you've assigned such a lambda expression to a Func<> type, you can't get the expression tree back.