Inherited Class using as datacontract

Actually I Have a Problem Using a Inherited Class as a DataContract. Below is My Code

[DataContract]
public class PartialTestClass
{
}

[DataContract]
public class TestClass : PartialTestClass
{
}

[ServiceContract(Name = "IMessageContract", 
CallbackContract = typeof(IMessageCallback))]
public interface IMessageContract
{
    [OperationContract]
    开发者_如何学PythonPartialTestClass Test(PartialTestClass partialTestClass);
}

Client Side:

PartialTestClass p = new TestClass();
p.Name = "Afshin.Ahmari";
TestClass p2 = (TestClass)Proxy.Test(p);

Can Anybody help me with this

---

Child classes need to be known types of the base class:

    [DataContract]
    [KnownType(typeof(TestClass))]
    public class PartialTestClass { }