Where else do we have parent-child / one-to-many relationships where we assign the children top-level resource ids? I've seen lots of applications that have used compound keys for a PK and not assigned globally unique keys to the model, it's not an uncommon software pattern. The only reason the "id" exists is because Cassandra would require you to have a globally unique key, and in this case it's just a make up of the 2 parts of the compound key, I could take it out the id from the model, probably.