Question

Should there be any problem passing this kind of a collection in WCF?

class Parent
{
  [DataMember]
  // some data members

  [DataMember]
  Child myChild;    
}

class Child : Parent
{
  [DataMember]     
  // some more data members

  [DataMember]
  Parent myParent;
}

Should there be any problem passing a list of Parent?

I get strange results, sometimes the channel faults, sometimes it doesn’t fault but gives me no data until I remove all the children from the list.

Answer 1

First of all, you need to put the [DataContract] on every class that you want to have serialized and deserialized by WCF – it is not automatically inherited!

[DataContract]
class Parent
{
   .....
}

[DataContract]
class Child : Parent
{
   .....
}

If you’re dealing with collections of things, then you might need to check into the CollectionDataContract :

[CollectionDataContract]
[KnownType(typeof(Parent))]
[KnownType(typeof(Child))]
public class CustomCollection : List<Parent>
{
}

Also, WCF and SOA in general are quite a bit different from OOP and don’t handle inheritance all that well. You will most likely have to put [ServiceKnownTypes] or [KnownType] attributes on your service contracts in places where you want to use and support polymorphism.

So if you have a service method that accepts a Parent, but should also be able to accept a Child instance as well, then you need to decorate the method with the [KnownType] attribute to make this information available to WCF.

See the MSDN Documentation on the KnownType attribute, or check out this other SO question on the topic.

Marc