Silverlight, EDM/LINQ, and WCF Web Service - How to pass collections to Silverlight

Question

What is the proper way to pass an answer (a collection) back to Silverlight?

For example, if I have a service application that sits on top of the Northwind sample database and the service has a method called GetEmployees(). What is the proper "thing" to pass back to Silverlight? An IQueryable ?

Then considering the Async/Result casting stuff on the Silverlight side what do I cast it too? An IQueryable ?

UPDATE:
Is it the declaration of [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] that allows a remote client to see the structs (entities) from a service?? I didn't know there was such thing as a Silverlight-friendly-WCF class so thats not what I started with. Once I added that attribute in the solution wouldn't let me use the service any more without it. So I could not test what I was seeing before. Any thoughts on what AspNetCompatibilityRequirementsMode.Allowed does under the hood?

UPDATE 2:
See comments to Terry Donaghe.

Answer 1

In using regular web services, you have to return collections like List the SOAP formatter to know what to do with it. However, I have not used WCF, so I don't know if that does things differently.

Answer 2

Just return a List. If you can return a single T, then you can return a List<T>.

Answer 3

Did you just try passing arrays of base types around? Unless you create DataContracts, WCF doesn't know what any of your objects are. When you try to pass a List WCF really just passes an array since it's designed to try to be inter-operable.

Define a DataContract to contain information about the Employees (or whatever). Try to keep it relatively simple. When you create your proxy (probably with svcutil or Add Service Reference) VS2008 will auto-magically define the DataContracts on your client side and then you can use them just like a regular object.

I prefer to use WCF manually - I create my own contract, implementation and proxy dlls. Doing that gives me a great deal of flexibility as far as de-serialization and other stuff is concerned. For more on that, see these two references:

WCF the Manual Way, the Right Way

Manual WCF - an Extension

Also, please see Chapter 3 of the WCF Bible, "Programming WCF Services" by Juval Lowy. It's chock full of info on DataContracts.