"Reuse types in all references assembiles" - Problem

Question

WCF service: (uses a model in a .dll. One function returns a model that has changed)
- Client 1 (updates web reference, proxy is set to "reuse types in referenced assemblies")
- Client 2 (does nothing, proxy is set to "reuse types in referenced assemblies")
The problem:
When Client 2 calls the service and gets the model, some of the model contains null data (because the model has changed), but no error occurs! This is very dangerous, so what's the solution?
Would the problem go away if Client 1 and Client 2 would force the proxy to generate classes (uncheck "Reuse types in references assembiles")?
Thanks,
Gunnar

Answer 1

Model? Are you talking about a domain model? A model should not be used. If anything, you should be using DTO(s) in a classlib project that all projects within the solution know about the DTO(s), which is an abstraction away from the model. The classlib
project can be called Entities. In that way, the WCF cleint and WCF service flatout do not care if a DTO changes. 
http://en.wikipedia.org/wiki/Data_transfer_object
Secondly, you should be using request and reponse objects where the response objects return data to the client (those DTO(s) and/or error objects with error messages that are checked on the client-side. In that way, sending and receiving request/response
objects, WCF flatout doesn not care if the objects change.
http://thatextramile.be/blog/2009/11/requestresponse-service-layer-requests-and-responses/