Webservice Response is turned into ref parameter when using MessageContract

Question

I have defined the following Interface

[ServiceContract]
public interface IHealthProducts
{
    [OperationContract()]
    ResponseClass OrderSelfSignedHealthCertificate();
}

Which returns the following type

[MessageContract]
public class ResponseClass
{
    [MessageBodyMember]
    public string AnimalSpeciesCode
    {
        get;
        set;
    }

    [MessageBodyMember]
    public int VBN
    {
        get;
        set;
    }
}

I expected that the generated client code would expose the OrderSelfSignedHealthCertificate method in the following way:

HealthProductsClient client = new HealthProductsClient();
ResponseClass response = client.OrderSelfSignedHealthCertificate();

Instead, the properties of ResponseClass aren't wrapped in the ResponseClass, but exposed like so:

string OrderSelfSignedHealthCertificate(out int VBN)

When I exchange the MessageContract for a DataContract attribute and the MessageBodyMember for a DataMember attribute, I get the expected behaviour (ResponseClass response type). I need the MessageContract however, because I need to put some of the properties in the SOAP header.

Am I doing something wrong? Is this normal behaviour? How do I get a ResponseClass return type, when using a MessageContract?

Any help greatly appreciated.

Answer 1

When your [MessageContract] contains more than one [MessageBodyMember], then WCF will return the first one as return value from the service call (AnimalSpeciesCode in your case), and all others are returned as out or ref paraemters.

You can solve this by having only a single [MessageBodyMember] in your message contract that encapsulates all items you need to have return, something like this:

[DataContract]
class CompoundData
{
    public string AnimalSpeciesCode { get; set; }
    public int VBN { get; set; }
}

[MessageContract]
public class ResponseClass
{
    [MessageBodyMember]
    public CompoundData Payload { get; set; }
}

In this case, the CompoundData should be the return value from your service call - containing both elements you need.

Answer 2

Thanks Marc, that did it. I made a generic ResponseWrapper class to encapsulate the return types:

[MessageContract(WrapperNamespace = "http://mynamespace.com")]
public class ResponseWrapper<T>
{
    [MessageBodyMember(Namespace = "http://mynamespace.com")]
    public T Response
    {
        get;
        set;
    }
}

I have defined the returntype of OrderSelfSignedHealthCertificate to be

ResponseWrapper<ResponseClass> OrderSelfSignedHealthCertificate();

In my client code this translate to

ResponseClass OrderSelfSignedHealthCertificate(); 

Which is what I wanted. Thanks!

Answer 3

I have posted a follow-up to this question here. Generic return types aren't named properly when using a MessageContract.