WCF中MessageContract的KnownType

Question

I am using Stream object inside my wcf Contracts so forced to use MessageContract instead of DataContract .

 [MessageContract]
    public class Document 
    {
        [MessageBodyMember(Order = 1)]
        public System.IO.Stream FileData;

}

 [MessageContract]
    public class A : Document 
    {
        [MessageBodyMember]
        public string input;

}

 [MessageContract]
    public class B : Document 
    {
        [MessageBodyMember]
        public string someProp;

}

[ServiceContract]
    public interface ISomeService
    {

        [OperationContract]
        Document SomeMethod(Document file);
}

I want the consumer of this service to create object of either A or B and call the service with it. On the service side, I can type cast it to proper object then perform some action.

Problem is I cannot specified KnownType with MessageContract and inherited contracts cannot be exposed to client until they are used in service or declared with KnownType .

I tried google it but couldn't find anything related to KnownType with MessageContract .

As suggested in comment... i updated my message contract with KnownType but they are still not exposed to client through service reference...

[MessageContract]
    [KnownType(typeof(FileSystemStoredDocument))]
    [KnownType(typeof(FileBoundStoredDocument))]
    [KnownType(typeof(SharepointStoredDocument))]

    public class Document : DocumentInfo, IDisposable
    {
}

Can any one help me what's wrong here?

Note : ALL KnownType are inherited from Document

Answer 1

Message contracts describe exactly how the message should look like . They do support inheritance, but you must specify the exact message contract you're using in a specific operation.

If you check the body parts of the message:

ContractDescription.GetContract(typeof(ISomeService)).Operations[0].Messages[0].Body.Parts

You'll see exactly one part - a Stream object. That's in contrast to data contracts, where the body contains a part of the type Object . So you see why KnownType wouldn't work here .

(The ContractDescription class is used, among other things, to generate WSDL. See the WsdlExporter class.)

What you can do is create a hierarchy of data contracts that would be contained in the message contract, eg

[MessageContract]
public class Document 
{
    [MessageHeader]
    public DocumentProperties Properties;

    [MessageBodyMember(Order = 1)]
    public System.IO.Stream FileData;
}

[DataContract]
[KnownType(typeof(A))]
[KnownType(typeof(B))]
public abstract class DocumentProperties { }

[DataContract]
public class A : DocumentProperties 
{
    [DataMember]
    public string input;
}

[DataContract]
public class B : DocumentProperties 
{
    [DataMember]
    public string someProp;
}

Note that you you cannot have more than one body member if you want to pass a Stream , so the rest of the properties must be in headers.