WCF DataContract/inheritance

[THY02K]

Problem: trying to wire down the following class through WCF and run into deserialization problem:

[KnownType("GetKnownType")]
[DataContract(Name = "Person", Namespace="xxxxx.Util")]
public class Person : IPerson, IGenericObjectOwner
{
#region KnownType attribute - Generic type, REF: http://msdn.microsoft.com/en-us/library/ms730167.aspx
private static Type[] GetKnownType()
{
Type[] t = new Type[3];
// t[0] = typeof(xxxxx.Util.Security.SystemUser); // I purposedly comment this out for reasons below.
t[0] = typeof(xxxxx.Util.Generic.GenericObject);
t[1] = typeof(xxxxx.Util.Security.BasicAudit);
t[2] = typeof(xxxxx.Util.Name);
return t;
}
...
[DataMember()]
public IGenericObject GenericObj { get... set...} // interface IGenericObjectOwner contains an IGenericObject (which contains parent/child Person)

}

[DataContract(Name = "SystemUser", Namespace = "xxxxx.Util.Security")]
[GenericObjectAttribute(ObjectClassifier = "Person")]
public class SystemUser : Person, ISystemUser
{
...
}

public interface IGenericObjectOwner
{
IGenericObject GenericObj
{
get;
set;
}
...
}

public class GenericObject : IGenericObject
{
...
[DataMember()]
public virtual List<IGenericObjectOwner> Parents // IGenericObject has "Parents" and "Children"
{
// Commenting this out fixed the person proxy/serialization problem mentioned below
/*
get { return _lstParents; }
set { _lstParents = value; }
*/

get { return new List<IGenericObjectOwner>(); }
set { }
}

[DataMember()]
public virtual List<IGenericObjectOwner> Children
{
// Commenting this out fixed the person proxy/serialization problem mentioned below
/*
get { return _lstChildren; }
set { _lstChildren = value; }
*/

get { return new List<IGenericObjectOwner>(); }
set { }
}
...
}


I checked Reference.cs,

[System.ServiceModel.OperationContractAttribute(Action="http://tempuri.org/ISecurityService/GetPerson", ReplyAction="http://tempuri.org/ISecurityService/GetPersonResponse")]
[System.ServiceModel.ServiceKnownTypeAttribute(typeof(xxxxx.Util.Security.SystemUser))] << QUESTION: Why is it not xxxxx.Util.Person?
...
xxxxx.Util.Person GetPerson(string strEmail);


And when I actually invoked the Service, I keep getting this error:

Type 'PersonProxy9ab9661107bd4ad9a11c877daa3d0e7d' with data contract name 'Person:xxxxx.Util' 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.


I then proceed to modify Reference.cs manually to add xxxxx.Util.Person to known type (replace "xxxxx.Util.Security.SystemUser" above"), I still end up with the same error.

My mind is not really functioning now after long struggles with this last few days but I stumbled on this:

http://eddiedebear.blogspot.com/2008/05/wcf-and-inheritance.html

Not sure if it has to do with IExtensibleDataObject but I gave it a try and did NOT resolve the problem. Read further and figured out that IExtensibleDataObject only has to do with versioning (not what I'm facing right now, see this: http://codeidol.com/csharp/wcf/Data-Contracts/Versioning)
Thanks and hope someone can point me to right direction in this regards.

[THY02K]

does it has to do with NHibernate? Person is loaded using NHibernate like this on server side:

Person oPerson = null;
PersonDAO oPersonDAO = new PersonDAO();
oPersonDAO.OpenSession();
oCriteria = oPersonDAO.DBSession.CreateCriteria(typeof(Person));
oCriteria.Add(Expression.Eq("PrimaryEmail", strEmail));
lstResult = oPersonDAO.Find(oCriteria, Int32.MaxValue);
if (lstResult.Count > 0)
{
oPerson = (Person) lstResult[0];
return oPerson;
}


oPerson is a "xxxxx.Util.Security.SystemUser", it's also a "xxxxx.Util.Person" but certainly not a proxy (I checked it on NHibernate debugger). Also it doesn't look like it has to do with NHibernate lazy load even though problem arises from Person.GenericObject.Parents/Children collection because Parents/Children are not populated by NHibernate - it's done by code I wrote myself so no lazy loading issue here.

[THY02K]

Sorry I just found out the children is indeed NHibernate proxies


[PersonProxya4d5a6ec378c4c049f205902f1912564] {xxxxx.Util.Security.SystemUser, PersonId:0, Logon:guest, PasswdHash:159802048,ThinkFundamentals.Util.Person, Id:2, Name:xxxxx.Util.Name, FirstName:guest, MiddleName:, LastName:guest, PrimaryEmail:guest@xxxxx.com, Type:undefined, GenericObj:object type: xxxxx.Util.Generic.GenericObject, object name: , object classifier: Person, TypeName: ThinkFundamentals.Util.Person, DAOTypeName: xxxxx.Util.PersonDAO, Util, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null, DAOCreateInstanceArg: , CreateDate: 3/18/2009 10:40:19 AM, Properties: , Parents:, Children:, BasicAudit:ThinkFundamentals.Util.Security.BasicAudit, CreateDate:3/18/2009 10:37:48 AM, CreatedBy:1, LastUpdate:3/18/2009 10:37:48 AM, LastUpdateBy:1} PersonProxya4d5a6ec378c4c049f205902f1912564
__interceptors {Castle.Core.Interceptor.IInterceptor[1]} Castle.Core.Interceptor.IInterceptor[]


Any suggestion? seems like I'd need to do a lot of Googling... but at least root cause found... further suggestion in dealing with NHibernate proxy/WCF be very good, anyone?! I can't add [DataContract] to NHibernate proxy...

[THY02K]

I found the answer!!!!!!!!!!

Instead of calling NHibernate ISession.Load, I called ISession.Get - you'd get an instance of xxxxx.Util.Person instead of the NHibernate proxy.

Hurrah!!