How to expose a web method with Func parameter?

Question

I wonder if I could expose a web method with Func parameter!

[WebMethod]
public List<Entity> ReadEntities(Func<Entity, bool> predicate)
{
    using (var entities = new GwEntities())
        return entities.Entities.Where(predicate).ToList();
}

When I tried to update the web reference I had an exception from Visual Studio that:

System.Func[GwModel.Entity,SystemBoolean] caonnot be serialized because it does not have a parameterless constructor

Any workaround please!

You want callers of a web service to be able to pass arbitrary executable code in? Can you think of any reasons why this might be a bad idea? — AakashM, Apr 25 '11 at 10:41
@AakashM: hmmm, don't think of it as executable code. It's a predicate with a custom class as input and bool for output. But seems you're right, the user can do more than that. Thanks for notification. — Homam, Apr 25 '11 at 10:45
Keep in mind the client need not even be .NET; this is ***never*** going to work. You need a new strategy. — Marc Gravell, Apr 25 '11 at 10:49

score 4 · Accepted Answer · edited May 05 '11 at 17:07

4

You cannot serialize your own code like this. Where should the serializer start and where stop? Should it transfer only the code of your method and all assemblies that are called from within the method? LINQ to objects does something similar. You should have a look at Expressions. These can be serialized across the wire.

edited May 05 '11 at 17:07

John Saunders

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answered Apr 25 '11 at 10:23

Alois Kraus

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There is also a question discussing that: http://stackoverflow.com/questions/217961/serializing-and-deserializing-expression-trees-in-c – ChrisWue Apr 25 '11 at 10:49

score 2 · Answer 2 · answered Apr 25 '11 at 10:47

2

No can do. If you think of the func parameter as a reference to some code on the caller's side, how do you expect the server to be able to see that code?

answered Apr 25 '11 at 10:47

geofftnz

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score 1 · Answer 3 · answered Apr 25 '11 at 10:41

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i think you might not be able to implement client callbacks with classical asp.net web services. you can opt for WCF for this. KickStart.

answered Apr 25 '11 at 10:41

Mubashir Khan

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How to expose a web method with Func parameter?

3 Answers3