[Dev Tip] DataContract in WCF

[KnownType(typeof(UserAttribute))]
[KnownType(typeof(RepeatingUserAttribute))]
[XmlInclude(typeof(UserAttribute))]
[XmlInclude(typeof(RepeatingUserAttribute))]
public class UserAttributes : KeyedCollection<string, AbstractUserAttribute>

[DataContact]
AbstractUserAttribute

Ref service
=> Array of AbstractUserAttribute

[KnownType(typeof(UserAttribute))]
[KnownType(typeof(RepeatingUserAttribute))]
[XmlInclude(typeof(UserAttribute))]
[XmlInclude(typeof(RepeatingUserAttribute))]
[CollectionDataContract]
public class UserAttributes : KeyedCollection<string, AbstractUserAttribute>
=> UserAttributes