# File lib/mongoid/relations/synchronization.rb, line 77
      def update_inverse_keys(meta)
        return unless changes.has_key?(meta.foreign_key)
        old, new = changes[meta.foreign_key]
        adds, subs = new - (old || []), (old || []) - new
        meta.criteria(adds).add_to_set(meta.inverse_foreign_key, id) unless adds.empty?
        meta.criteria(subs).pull(meta.inverse_foreign_key, id) unless subs.empty?
      end