cache_joined_association

# File activerecord/lib/active_record/associations.rb, line 1925
            def cache_joined_association(association)
              associations = []
              parent = association.parent
              while parent != join_base
                associations.unshift(parent.reflection.name)
                parent = parent.parent
              end
              ref = @associations
              associations.each do |key|
                ref = ref[key]
              end
              ref[association.reflection.name] ||= {}
            end