instance method add_counter_cache_callbacks

# File activerecord/lib/active_record/associations.rb, line 1361
        def add_counter_cache_callbacks(reflection)
          cache_column = reflection.counter_cache_column

          method_name = "belongs_to_counter_cache_after_create_for_#{reflection.name}".to_sym
          define_method(method_name) do
            association = send(reflection.name)
            association.class.increment_counter(cache_column, association.id) unless association.nil?
          end
          after_create(method_name)

          method_name = "belongs_to_counter_cache_before_destroy_for_#{reflection.name}".to_sym
          define_method(method_name) do
            association = send(reflection.name)
            association.class.decrement_counter(cache_column, association.id) unless association.nil?
          end
          before_destroy(method_name)

          module_eval(
            "#{reflection.class_name}.send(:attr_readonly,\"#{cache_column}\".intern) if defined?(#{reflection.class_name}) && #{reflection.class_name}.respond_to?(:attr_readonly)"
          )
        end