Question

If I have a Server/Client application that both reference the same DLL which contains interfaces used for a REST server and for the WebChannelFactory to reference the web server, what would happen to legacy clients if the Servers interface gets and update? For example say version one of an application gets pushed out with the following interface:

[ServiceContract]
public interface ISampleInterface
{
    [OperationContract]
    [WebInvoke(UriTemplate = "/PutDevice", ResponseFormat = WebMessageFormat.Xml, RequestFormat = WebMessageFormat.Xml)]
    void PutDevice(Device device);
}

[DataContract(Namespace = "")]
public class Device
{
    [DataMember]
    public Guid id { get; set; }

    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public string Description { get; set; }
} // End of Device

This is what the REST service uses as a contract and the agent would have code similar to the following:

WebChannelFactory<ISampleInterface> client = new WebChannelFactory<IGridVisionService>(new Uri(targetHost));
ISampleInterface sampleInterface = client.CreateChannel();
sampleInterface.PutDevice(new Device() { id = Guid.Empty(), Name = "Test Device", Description = "Test Device Description" });

So the client application is already deployed to hundreds of computers, but we realize for the version we also want the client to send it’s domain so we modify the device data contract to be the following:

[DataContract(Namespace = "")]
public class Device
{
    [DataMember]
    public Guid id { get; set; }

    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public string Domain { get; set; }

    [DataMember]
    public string Description { get; set; }
} // End of Device

It’s easy to update the server, but now there are hunders of agents that do not know about the Domain. What is the proper way to deal with this situation? My only thought was to not use a DataContract but an XElement that I could manually parse. Then add login to the Server for dealing with the case of a missing Domain, but this seems sloppy. Is there a better solution that I am overlooking?

Answer 1

I was able to test this myself. In the case that my Client Device linking to a dll that did not know about the Domain parameter, the method call still succeeded and the Domain parameter was simply null. This is the result I was hoping for!