update_counters

# File activerecord/lib/active_record/associations/belongs_to_association.rb, line 44
        def update_counters(by)
          if require_counter_update? && foreign_key_present?
            if target && !stale_target?
              target.increment!(reflection.counter_cache_column, by)
            else
              klass.update_counters(target_id, reflection.counter_cache_column => by)
            end
          end
        end