I just successfully implemented a WF4 "versioning" system using WCF's Routing Service. I had a version1 workflow service to which I added a new Decision activity and saved it as a version2 service. So now I have 2 endpoints (with identical service contracts, i.e. all Receive activities are the same for both service) and a router that checks the content of a message (a "versionId" string on the object that all of my Receive's accept as an argument) to decide which endpoint to hit.
My question is, while this works fine when no changes are made to the service contract, how to I handle the need to add or remove methods from my service contract and create a version3 service? My original thought was, when I add the service reference to my client, I use the latest workflow service's endpoint to get the latest service contract. Then, in the config file, I change the endpoint I connect to to the router's endpoint. But this won't work if v1 and v2 have a different contract than v3. My proxy will have v3's methods and forget all about v1 and v2.
Any ideas of how to handle this? Should I create an actual service contract interface in my workflow solution (instead of just supplying a ServiceContractName in my Receive activities)?
If the WCF contract changes your client will need to be aware of the additional operations and when to call them. I have used the active bookmarks, it contains the WCF operation, from the persistence store in some applications to have the client app adapt to the workflow dynamically by checking the enabled bookmarks and enabling/disabling UI controls based on that. The client will still have to be updated when new operations are added to a new version of the workflow.