update_counters

# File activerecord/lib/active_record/associations/belongs_to_association.rb, line 27
        def update_counters(record)
          counter_cache_name = reflection.counter_cache_column

          if counter_cache_name && owner.persisted? && different_target?(record)
            if record
              record.class.increment_counter(counter_cache_name, record.id)
            end

            if foreign_key_present?
              klass.decrement_counter(counter_cache_name, target_id)
            end
          end
        end