instance method collection_reader_method

# File activerecord/lib/active_record/associations.rb, line 1477
        def collection_reader_method(reflection, association_proxy_class)
          redefine_method(reflection.name) do |*params|
            force_reload = params.first unless params.empty?
            association = association_instance_get(reflection.name)

            unless association
              association = association_proxy_class.new(self, reflection)
              association_instance_set(reflection.name, association)
            end

            reflection.klass.uncached { association.reload } if force_reload

            association
          end

          redefine_method("#{reflection.name.to_s.singularize}_ids") do
            if send(reflection.name).loaded? || reflection.options[:finder_sql]
              send(reflection.name).map { |r| r.id }
            else
              if reflection.through_reflection && reflection.source_reflection.belongs_to?
                through = reflection.through_reflection
                primary_key = reflection.source_reflection.primary_key_name
                send(through.name).select("DISTINCT #{through.quoted_table_name}.#{primary_key}").map! { |r| r.send(primary_key) }
              else
                send(reflection.name).select("#{reflection.quoted_table_name}.#{reflection.klass.primary_key}").except(:includes).map! { |r| r.id }
              end
            end
          end

        end