Why use a "RIA Services Link" instead of just an OData endpoint?

Question

Before reading, please know I've read all the other posts about the differences between vanilla WCF, WCF Data Services and RIA Services. My question is specifically about why RIA Services is being considered as a special kind of data source specifically for Silverlight when it seems to make more sense to just have it do one job: serve as a business logic layer behind a REST interface.

It looks like with the release of VS2010, RIA Services has solidified its stance as a business logic layer that sits behind a REST data access service - this seems to be confirmed by the new "Expose OData Endpoint" option on the Domain Service Class template in Visual Studio, which as far as I can tell essentially does for your RIA Service exactly what WCFDS does for an arbitrary data source (you could do this before, I believe, but the addition of this checkbox makes it clear that a RIA Service can be viewed as a layer containing business logic used to enhance a REST data endpoint and/or constraint it to a given set of queries, and not necessarily an endpoint in and of itself).

So, if I've got a RIA service with business logic, exposed via OData, I can add a reference to the OData service from a WCF client app. On the client, I get a DataServiceContext derivative that lets me do unit-of-work style work on the client. I can do the same thing from a Silverlight app and get what appears to be the same thing - a DataServiceContext derivative.

If I instead use a "RIA Service Link" in my Silverlight app to directly tie the app to the RIA service instead of adding a service reference, I get code generated by Visual Studio that appears to support pretty much the same patterns of work, but using a different style of API.

That being the case:

• What are the advantages of a "RIA Services link," where a Silverlight app is tied directly to a RIA Service, as opposed to just adding a service ref to an OData endpoint that can be consumed by any kind of client without incurring tight coupling? I'm told that the magic of RIA is in the code generation, so I guess I'm trying to understand how the RIA code generation differs so much from "add service reference" code generation.
• If there are advantages, why are these advantages made available specifically to Silverlight and not WCF client apps? Selling RIA services purely as a layer behind an OData endpoint seems like it would help standardize and push OData even further in terms of becoming a universal type of endpoint for any sort of client – “consume from ASP, consume from Silverlight, consume from WCF… you get virtually the same experience and it’s a great one.” Instead, we have Silverlight tied directly to RIA with a special set of functionality, and all other clients using the open protocol.

Answer 1

RIA services is not intended as "Domain logic behind oData" to the contrary and quite the opposite. The intention of RIA services is to abstract away the mechanics of web based data access to enable Rapid Application Development in Silverlight. Think of RIA Services as to WCF as VB is to C++.

The key benefits of RIA Services are:

Transparent Data Access - there's no fiddling with svc files etc. You create an entity framework model, wrap it in a domain service and you're done. More importantly changes are propagated automagically. The developer doesn't have recreate the Service reference every time the model or a query changes, code gen does it for you.

Authentication framework out the box - It's there when you create a business app, it's a template in VS, a way to integrate with existing ASP.NET auth without having to do any heavy lifting.

Data Source Templates and Validation = Probably one of the most overlooked features but yet one of the most important. Have you opened the "data sources" window? RIA services creates User configurable DataContext bound Master/detail controls that support server side validation annotations. A functional data bound app is a drag and drop away. Consider the value of that to someone who is more Design/Blend focused.

In short RIA services is built for a developer to be able to go from an edmx data model to a secure functional Silverlight up in a matter of hours. It's awesome stuff when used in context.

As a note, I've done quite a bit of research on RIA Services and Data Services and they fulfill different needs. We use RIA Services for all our desktop replacement apps, but we use Data Services for SaaS.

I don't think you're far off with the long term intention of RIA services though. I think we'll see oData and RIA services get a lot closer in future versions.

Answer 2

The OData endpoint exposed by WCF RIA Services does not support query operations and returns data as-is. That means no benefit from IQueryable, sorting, parameters, etc. It will simply expose your methods; end of story. There is rumor that this will change in the next release however. However, what RIA Services provides from the standpoint of IQueryable on service calls, automatic propagation of business rules from the middle tier to the UI, and INotifyDataErrorInfo for flowing validation errors to the Silverlight client is outstanding should you choose to leverage them.