WCF Service object serialization

Question

I have one abstract class named contact and another class called client that inherits from contact. I'm dealing with a WCF Service with a method that takes a parameter of type contact. however what I have is an instance of client that I want to pass. Im facing this Error:

Type 'xxx.Client' with data contract name 'Client:http://schemas.datacontract.org/2004/07/xxx' 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.

Answer 1

you ned to let DataContractSerializer know that a Client is a type of Contact.

There are several ways to do this, but they all revolve around using the KnownType attribute or the ServiceKnownType attributes.

The KnownType can be placed on the Client class to tell DataContractSerializer that it is a KnownType of Contact.

[DataContract]
[KnownType(typeof(Client))]
public class Contact{}

The KnownType can also be placed on a class to indicate that when serialising this class you may also encounter this other class.

You may want to do this if you have a DataContract class that has a property which is a Contact which may actually contain a Client:

[DataContract]
[KnownType(typeof(Client))]
public class Meeting
{
    Contact MeetingContact{get;}
}

In this case you could get away without specifying the KnownType on the Client. You may also want to do this if you have a property which returns a collection and you want to specify the types which can be in the collection.

You may, instead of specifying the actual type of the KnownType, specify the name of a static method which will return the known types instead:

[DataContract]
[KnownType("GetKnownTypes")]
public class Meeting
{
    Contact MeetingContact{get;}

    private static Type[] GetKnownType()
    {
    return new Type[]{typeof(Client)};
    }
}

You can also specify the known type through the configuration file.

ServiceKnownTypes work in a similar way, but are specified on the Service itself:

[ServiceKnownType(typeof(Client))]
[ServiceContract()]
public interface IMyServiceContract
{

    [OperationContract]
    Contact GetContact();
}

This set up will let the DataContactSerializer know that any of the methods may return a type of type Client. In a similar way to the known types you can also use a static method to provide the service known types.