.NET Framework - WCF 3.5 and Problem with KnownTypeAttribute

Asked By coconet

29-Feb-08 11:34 AM

I have an Interface and an implementing class (receiver) and calling
class (sender) in a single DLL. The DLL is referenced in a web site
that received WCF calls and also in a seperate web site that makes
calls to the WCF site .svc. Why would I get an Exception about
KnownTypeAttribute?


InnerException thrown is:

System.Runtime.Serialization.SerializationException: Type
'nstestSecurity.TestPrincipal' with data contract name
'TestPrincipal:http://schemas.datacontract.org/2004/07/nstest.Security'
is not expected. Add any types not known statically to the list of
known types - for example, by using the KnownTypeAttribute attribute
or by adding them to the list of known types passed to
DataContractSerializer..

But my stuff looks like this:

[KnownType(typeof(IPrincipal))]
[DataContract(Name="DashboardPrincipal")]
public class TestPrincipal : IPrincipal
{
....
}

An instance of TestPrincipal is one of two parameters for a class that
uses this interface:

[ServiceContract(Name="IWcfReceiver",Namespace="http://nstest/200804/IWcfReceiver")]
public interface IWcfReceiver
{
[OperationContract]
List<ITestStuff> Do( IPrincipal inputPrincipal , List<ITestStuff>
testList );
}

02-Mar-08 10:42 PM

Hi coconet,

Regarding on the "Type not serializable" exception you encountered, it is a
typical error in WCF service when you use base class/interface with derived
classes actually send in WCF service method.

For your case, the problem here is that you only declare the Interface type
in your WCF method( the IPrincipal type which is not a DataContract).
However, WCF service will only expose metadata for types that is decorated
with "DataContract" attribute or any type that is declared as "KnowType".
I saw the you've add "KnowTypeAttribute" in the "TestPrincipal" class, this
is not the correct means of using "KnownTypeAttribute".
interface) or on a DataContract type which has member of the base
type/interface. See the following reference:

http://msdn2.microsoft.com/en-us/library/ms730167.aspx

To address the problem in your case, since you haven't use a base class,
you can add the known type declaration at service contract level. e.g.

=========
[ServiceContract]
[ServiceKnownType(typeof(TestPrincipal ))]
public interface IYourServiceInterface
....
==============

the following article include all the three means that can be used for
apply "KnownType" info for WCF service's  custom data contract:

http://footheory.com/blogs/bennie/archive/2007/07/28/handling-data-contract-
object-hierarchies-in-wcf.aspx

Sincerely,

Steven Cheng

Microsoft MSDN Online Support Lead



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--------------------

ceiver")]

06-Mar-08 03:21 AM

Hi,

Found a solution to your problem? I'm having a simular issue where I get the knowType exception

/Marc

BizTalk Utilities - Frustration free BizTalk Adapters
http://www.topxml.com/biztalkutilities

08-Apr-08 11:14 PM

I got into something else and don't remember what the fix should be,
after some more research I think I got it but did not actually
implement a solution.

I think the problem has to do with my using a List<T> of an Interface
for a return type and for a parameter. Whent he List<T> is serialized,
the receiver expects an array of a concrete type that it can convert
to the list of a type. When passing a list of Interface, the class
that implements it could be "anything" so it doesn't rehydrate
properly.

I think I was being too lazy in hoping I could just pass things around
this way, I am pretty sure that changing the method signature to
take/receive an array of each concrete type (instead of a single
method that gives/expects a List of Interface) would work.