Nested List serialization - wcf

Question

I am having problem transfering my object from WCF to SL3.
interface IComposite {
ICollection<Child_A> Children{ get; set; }
}
[DataContract]
[knownType(typeof(ChildCollection))]
[knownType(typeof(ICollection<Child_A>))]
class Composite : IComposite {
ChildCollection c = null;
[DataMember]
public string Name { get;set;}
[DataMember]
public ICollection<Child_A> Children { get {
return c??(c=new ChildCollection());
} set;}
}
[CollectionDataContract]
class ChildCollection : List<Child_A> {
}
[DataContract]
class Child_A {
[DataMember]
string Name { get;set; }
}
[OperationContract]
Composite GetData(){
var data = new Composite();
data.Children.Add( new Child_A() { Name = "child_a_1" } );
return data;
}
When I call the service from SL3, I get the Composite object but no item in the list. There are other collection in Composite. When I set [DataMember(Order=0/1)] I get error nullreference error on client. And if I remove it, I get error Not Found. I tried KnowType and ServiceKnownType but did not work. I checked svcTrace, it simply says Serialization Error. Where I am doing wrong.
SVC TRACE
The InnerException message was 'Type 'xxxCoverageEntity' with data contract name 'xxxCoverageEntity : http://schemas.datacontract.org/2004/07/xxxBusinessEntities' is not expected. Add any types not known statically to the list of known types
Here xxxCoverageEntity is Child_A in sample

Answer 1

You need to annotate the collection with DataMember or it will not get serialized at all. You will also need to annotate the DataContract with KnownType(typeof(ChildCollection)) as otherwise it doesn't know what type of "thing" the ICollection is and therefore how to serialize it
Similarly you will need to add [DataMember] to Child_A Name property or it will not get serialized