Problem is load_from_json is passed the primary_key attribute, but it is checking for id instead of primary_key.

Then it attempts to call hyperstack_internal_setter'your_primary_key_value' instead of _hyperstack_internal_setter_id. But that method is just a nop, so instead load_from_json should just add this guard:

target.send("hyperstack_internal_setter#{method}", value.first) unless method == target.class.primary_key

on about line 509