add_counter_cache_callbacks

# File activerecord/lib/active_record/associations/builder/belongs_to.rb, line 22
    def add_counter_cache_callbacks(reflection)
      cache_column = reflection.counter_cache_column
      foreign_key = reflection.foreign_key

      mixin.class_eval         def belongs_to_counter_cache_after_create_for_#{name}          if record = #{name}            record.class.increment_counter(:#{cache_column}, record.id)            @_after_create_counter_called = true          end        end        def belongs_to_counter_cache_before_destroy_for_#{name}          unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == #{foreign_key.to_sym.inspect}            record = #{name}            if record && !self.destroyed?              record.class.decrement_counter(:#{cache_column}, record.id)            end          end        end        def belongs_to_counter_cache_after_update_for_#{name}          if (@_after_create_counter_called ||= false)            @_after_create_counter_called = false          elsif self.#{foreign_key}_changed? && !new_record? && defined?(#{name.to_s.camelize})            model = #{name.to_s.camelize}            foreign_key_was = self.#{foreign_key}_was            foreign_key = self.#{foreign_key}            if foreign_key && model.respond_to?(:increment_counter)              model.increment_counter(:#{cache_column}, foreign_key)            end            if foreign_key_was && model.respond_to?(:decrement_counter)              model.decrement_counter(:#{cache_column}, foreign_key_was)            end          end        end, __FILE__, __LINE__ + 1

      model.after_create   "belongs_to_counter_cache_after_create_for_#{name}"
      model.before_destroy "belongs_to_counter_cache_before_destroy_for_#{name}"
      model.after_update   "belongs_to_counter_cache_after_update_for_#{name}"

      klass = reflection.class_name.safe_constantize
      klass.attr_readonly cache_column if klass && klass.respond_to?(:attr_readonly)
    end