MVVM & WCF - View Model and Model Relationship

Question

I am not understanding how my model can be a WCF service. It makes sense when its an Astoria partial class residing on the client that allows remote calls to do persistence calls, but a WCF service doesn't have properties for model fields that can be used to update a data store.

Even if I could factor out an interface for a model/domain object class into a separate assembly, a silverlight project will not allow me to add that as a reference.

How should my ViewModel encompass my WCF calls? Ultimately the WCF will call a repository assembly implemented in Linq-to-Sql, but apparently those entities are not my model in this scenario, my WCF classes are?

Thanks for any guidance on this.

Also, posts I have read to give a frame of reference:

1. http://development-guides.silverbaylabs.org/Video/Silverlight-Prism#videolocation_0
2. http://blogs.conchango.com/davidwynne/archive/2008/12/15/silverlight-and-the-view-viewmodel-pattern.aspx
3. http://msdn.microsoft.com/en-us/magazine/dd458800.aspx

Answer 1

When you create a service reference to a WCF service in a Silverlight project it also generates an interface for that Service, this is similar to David Wynns IFeedService in the articles you listed above. The service reference will also generate proxy objects that represent the objects used by the service (Product, Category etc).

The important thing to note is that the service interface isn't the model, it's how you access the model. Going back to David's example, his ViewModel exposes a list of items (his model), this list is retrieved using the service.

If you're looking to share code between the client and server I'd reccomend looking into something like RIA Services. If this isn't for you then I'd look at a few articles around about sharing code between the server and client (via Add as Link).

Hope this helps

Answer 2

Yes, RIA Services. But why recommend them now, as they will be released only next year, at an undefined date.