IExtensibleDataObject usage in clients

Question

I have converted my web service to wcf service which has some datacontracts. As a best practice it is mentioned and advisable that the DataContracts should inherit from IExtensibleDataObject. I get the point that in case of addition or removal of datamembers, IExtensibleDataObject is helpful. But i am not able to get how will the clients access removed datamembers. Here is my code:

[ServiceContract(Namespace = "http://mycompany.com/2010/08/")]
public class MyWebService {
    [OperationContract]
    public Employee Add(Employee emp)
    {
        // Some Processing
    }
}

[DataContract(Name = "Employee", Namespace = "http://mycompany.com/2010/08/")]
public class Employee : IExtensibleDataObject {
    [DataMember] public string FirstName;
    [DataMember] public string LastName;

    public ExtensionDataObject ExtensionData  { get; set; }
}

Now in my next version of web service I made some changes to DataContract as

[DataContract(Name = "Employee", Namespace = "http://mycompany.com/2010/09/")]
public class Employee : IExtensibleDataObject {
    [DataMember] public string FirstName;
    [DataMember] public string LastName;
    [DataMember(IsRequired = true)] public string MiddleName;

    public ExtensionDataObject ExtensionData  { get; set; }
}

However my client that is accessing my older version of web service is now getting error for not supplying the MiddleName field. I am still confused for the usage of IExtensionDataObject.

Answer 1

I'm afraid that's not the correct usage of IExtensibleDataObject, the IExtensibleDataObject interface is designed to support version round-tripping, have a read of this MSDN article on forward compatibility:

http://msdn.microsoft.com/en-us/library/ms731083.aspx

And here's another article on best practices on Data Contract versioning in general: http://msdn.microsoft.com/en-us/library/ms733832.aspx