Using WCF with abstract classes

Question

How do I define DataContract for abstract classes in WCF?

I have a class "Person" which I communicate successfully using WCF. Now I add a new class "Foo" referenced from Person. All still good. But when I make Foo abstract and define a sub class instead it fails. It fails on the server side with a CommunicationException, but that doesn't really tell me much.

My simplified classes made for testing:

[DataContract] public class Person {     public Person()     {         SomeFoo = new Bar { Id = 7, BaseText = "base", SubText = "sub" };     }      [DataMember]     public int Id { get; set; }      [DataMember]     public Foo SomeFoo { get; set; } }  [DataContract] public abstract class Foo {     [DataMember]     public int Id { get; set; }      [DataMember]     public string BaseText { get; set; } }  [DataContract] public class Bar : Foo {     [DataMember]     public string SubText { get; set; } } 

Answer 1

I figured it out. You need to specify the subclasses on the abstract base class using "KnownType". The solution would be to add this on the Foo class:

[DataContract] [KnownType(typeof(Bar))] // <------ added public abstract class Foo {     [DataMember]     public int Id { get; set; }      [DataMember]     public string BaseText { get; set; } } 

Check out this link.

Answer 2

Interesting.

I would expect that code to fail in the Person constructor since you can't directly instantiate an Abstract Class.