Is removing a MessageBodyMember in a MessageContract considered a breaking change?

Question

Consider the following ServiceContract-Interface:

[ServiceContract]
public interface ITest
{
    [OperationContract]
    void MyMethod(MyClass obj);
}

With MyClass beeing:

[MessageContract]
public MyClass
{
    [MessageBodyMember(Order = 0)]
    public int A { get; set; }

    [MessageBodyMember(Order = 1)]
    public int B { get; set; }

    [MessageBodyMember(Order = 2)]
    public int C { get; set; }
}

MyClass is now changed to look like the following:

[MessageContract]
public MyClass
{
    [MessageBodyMember(Order = 0)]
    public int A { get; set; }

    [MessageBodyMember(Order = 2)]
    public int C { get; set; }
}

Would a client consuming this WCF-Service need to make additional changes to work with the new service definition?

Additionaly, what would happen if I were to additionally change C to have the new Order = 1?

Answer 1

If the client updates the WSDL File, it gets a syntax error in the code of the client, when the client calls the method.

The order element set on which position in the communication the bodymember sending to the server/client. You can see it into the svc log. Example.:

<ns2: myClass xmlns:ns2="yourNamespace">
<A xmlns=""></A>
<B xmlns=""></B>
<C xmlns=""></C>
</ns2:myClass>

After changed the ordner element:

<ns2: myClass xmlns:ns2="yourNamespace">
<C xmlns=""></C>
<A xmlns=""></A>
<B xmlns=""></B>
</ns2: myClass >

I have tried the example for you. I have used a WCF C# Web service and a C# client with a standard protocol: BasicHttpBinding. And I use the WCF Test client. In this combination I got no error in the client, provided that the client makes no WSDL update. In this case, you can change the order element without errors. But this is not a correct implementation; therefore you can’t assume that everything is working. For other clients see the result might be different. For example, a Java client is much more restrictive.