@Yash thanks for your reply. However my problem is that I do not know the set of fields (either on the root, or inside the array elements) - it is always changing and I don't want to have to update the spec every time someone adds a field. The spec should only know about parent.events and not assume the existence of any other field. I need a way to say "copy everything at the root, except for the parent field." What I've done for the moment is just implemented the logic in Jython - although it is fairly slow. ... View more