WCF & KnownType : Weird Behaviour

Question

Dear All,
I am new to WCF and I checked out the forum to find a solution but found nothing.
BTW, I have a base class called BaseData which is defined as bellow:

    [DataContract(Namespace = "http://localhost/KnownType")]
    [KnownType(typeof(SubData))]
    public class BaseData
    {
        [DataMember]
        public virtual int ID
        {
            get;
            set;
        }
    }

There is also a derived class called SubData:

    [DataContract(Namespace = "http://localhost/KnownType")]
    public class SubData :BaseData
    {
        [DataMember]
        public override int ID {get;set;}
    }

As you see SubData overrides ID property. Therefore, at client side, an instance of either BaseData or SubData must have a ID property. Bur surprisingly when I create a proxy using Visual Studio, I see that an instance of BaseData has an ID , but an instance of SubData doesn't. Why it is like that??
For your info I will bring the definition of the ServiceContract here:

[ServiceContract]
    public interface IKnownType
    {
        [OperationContract]
        SubData GetData();
    }

    [ServiceBehavior(Namespace = "http://localhost/KnownType")]
    public class KnownType : IKnownType
    {
        public SubData GetData()
        {
            return new SubData() { ID = 10 };
        }
    }

Answer 1

While creating proxy it doesnot create implementation for inherited class properties .

Other way is u can add your service reference in your client application and can accees
your ID property from both classes instances

---

Manesh

Answer 2

Hi Manesh
Thanks for the reply. May you please let me know what is the difference between creating a proxy and adding a WCF service reference?

Thanks

Answer 3

Adding a service reference generates the code for the proxy on the client side so they are basically the same thing (although creating a proxy could also mean instantiating an instance of the proxy class)

The contract defines what data is to be passed, it doesn;t define OO semantics for the classes contract. As far as the client is concerned it has a faithful representation of the data that the service exposes. A base class with an ID and a class that derives from it

---

Richard Blewett, thinktecture - http://www.dotnetconsult.co.uk/weblog2
Twitter: richardblewett

Answer 4

Hi AreFk, 

See  There is no probelm in your code. It is working fine for me .  You just remove your service refernece and add it again at client.  For your better undersatding , I have pasted 4 different combinations for  your code and 3rd and 4th combination is working fine. 

So , there is no probelem in your code 

1. Just rebuild the service 

2. Host it again 

3. update serveice reference at cleint and you are done my dear friend 

I tried out three combinations to answer you . 

First is  I replaced [DataContract]  of base class with Serilizable attribute. And I left service implentation as same of your implentation . 

    [Serializable]
    public class BaseData
    {
        [DataMember]
        public int ID { get; set; }
    }
    [DataContract]
    public class SubData:BaseData 
    {
        [DataMember]

        public int ID { get; set; }
    }
}

 Surprisngly at the client side ,  I  am getting two ID , ID1 ( I know , why I am getting two ID because , I am not overriding the ID field). But I am getting ID property exposed for the subclass .

            Service1Client proxy = new Service1Client();
            SubData obj = new SubData();
            obj.ID = 9;
            obj.ID1 = 10; 
            Console.WriteLine(obj.ID);
            Console.WriteLine(obj.ID1);
            Console.ReadKey(true);

Second , when I changed the class like below 

[Serializable]
    public class BaseData
    {
        [DataMember]
        public  virtual int ID { get; set; }
    }
    [DataContract]
    public class SubData:BaseData 
    {
        [DataMember]

        public  override  int ID { get; set; }
    }

I am not getting ID for either of the class.  where aas I am getting Idk_backingField. I am not sure whether, it is substitution of ID property  ?

            Service1Client proxy = new Service1Client();
            SubData obj = new SubData();
            BaseData baseobj = new BaseData();
            baseobj.IDk__BackingField = 10;
            obj.IDk__BackingField = 10;
            Console.WriteLine(obj.IDk__BackingField);
           Console.WriteLine(baseobj.IDk__BackingField);
            Console.ReadKey(true);
                     

3rd try which is youe solution 

I changed classes as

 [DataContract]
    public class BaseData
    {
        [DataMember]
        public  virtual int ID { get; set; }
    }
    [DataContract]
    public class SubData:BaseData 
    {
        [DataMember]

        public  override  int ID { get; set; }
    }

 and at the client side , I am getting ID property exposed for both of the classes . see the client code below. 

 Service1Client proxy = new Service1Client();
            SubData obj = new SubData();
            BaseData baseobj = new BaseData();
            obj.ID = 9;
            baseobj.ID = 10;
       
            Console.WriteLine(obj.ID);
           Console.WriteLine(baseobj.ID );
            Console.ReadKey(true);

So Id for both of the classes are exposed. 

Now coming to  your class definition 

 [DataContract(Namespace="http://localhost/KnownType")]
    [KnownType(typeof(SubData))]
    public class BaseData
    {
        [DataMember]
        public  virtual int ID { get; set; }
    }
    [DataContract(Namespace = "http://localhost/KnownType")]
    public class SubData:BaseData 
    {
        [DataMember]

        public  override  int ID { get; set; }
    }

 

At client side both Id is exposed .

            Service1Client proxy = new Service1Client();
            SubData obj = new SubData();
            BaseData baseobj = new BaseData();
            obj.ID = 9;
            baseobj.ID = 10;
            
       
            Console.WriteLine(obj.ID);
           Console.WriteLine(baseobj.ID );
            Console.ReadKey(true);
                     

---

Thanks Dhananjay Kumar
My Articles on http://www.c-sharpcorner.com/Authors/AuthorDetails.aspx?AuthorID=dhananjaycoder
Contact me at [e-mail]

Answer 5

Hi Dhananjay25 ,
Thank you very much for the exhaustive answer. I wrote that code within Visual Studio 2010 Beta 1 , is it possible to be a bug of VS?
I will check that code out in  VS 2008 and will be back to you :)

Thanks
Aref

Answer 6

Yes, it seems to be a bug in VS2010. I checked that code with VS2008 and it works fine.

Thank you all

Answer 7

Have u cheked with VS2010. R u getting the same behavior

---

Thanks Dhananjay Kumar
My Articles on http://www.c-sharpcorner.com/Authors/AuthorDetails.aspx?AuthorID=dhananjaycoder
Contact me at [e-mail]