with CartController.operations_batch(request.user):

            for category in cats:

                products = [

                    i for i in available_products

                    if i.category == category

                ]

                prefix = "category_" + str(category.id)

                p = _handle_products(request, category, products, prefix)

                products_form, discounts, products_handled = p

                section = GuidedRegistrationSection(

                    title=category.name,

                    description=category.description,

                    discounts=discounts,

                    form=products_form,

                )

                if products:

                    # This product category has items to show.

                    sections.append(section)

                    # Add this to the list of things to show if the form

                    # errors.

                    request.session[SESSION_KEY].append(category.id)

                    if request.method == "POST" and not products_form.errors:

                        # This is only saved if we pass each form with no

                        # errors, and if the form actually has products.

                        attendee.guided_categories_complete.add(category)