Re-structure some querying on cart and order pages to reduce load

src/pretix/base/models/orders.py

@@ -902,7 +902,7 @@ class Order(LockModel, LoggedModel):
 
     @property
     def positions_with_tickets(self):
-        for op in self.positions.all():
+        for op in self.positions.select_related('item'):
             if not op.generate_ticket:
                 continue
             yield op
@@ -1155,7 +1155,7 @@ class AbstractPosition(models.Model):
         (2) questions: a list of Question objects, extended by an 'answer' property
         """
         self.answ = {}
-        for a in self.answers.all():
+        for a in getattr(self, 'answerlist', self.answers.all()):  # use prefetch_related cache from get_cart
             self.answ[a.question_id] = a
 
         # We need to clone our question objects, otherwise we will override the cached

src/pretix/presale/checkoutflow.py

@@ -673,7 +673,7 @@ class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
         return ctx
 
 
-class PaymentStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
+class PaymentStep(CartMixin, TemplateFlowStep):
     priority = 200
     identifier = "payment"
     template_name = "pretixpresale/event/checkout_payment.html"

src/pretix/presale/templates/pretixpresale/event/order.html

@@ -313,7 +313,7 @@
         {% endif %}
         <div class="clearfix"></div>
     </div>
-    {% if order.user_change_allowed or order.user_cancel_allowed %}
+    {% if user_change_allowed or user_cancel_allowed %}
         <div class="panel panel-primary panel-cancellation">
             <div class="panel-heading">
                 <h3 class="panel-title">
@@ -321,7 +321,7 @@
                 </h3>
             </div>
             <ul class="list-group">
-                {% if order.user_change_allowed %}
+                {% if user_change_allowed %}
                     <li class="list-group-item">
                         <p>
                             {% blocktrans trimmed %}
@@ -335,7 +335,7 @@
                         </a>
                     </li>
                 {% endif %}
-                {% if order.user_cancel_allowed %}
+                {% if user_cancel_allowed %}
                     <li class="list-group-item">
                         {% if order.status == "p" and order.total != 0 %}
                             {% if order.user_cancel_fee >= order.total %}

src/pretix/presale/views/__init__.py

@@ -5,14 +5,14 @@ from functools import wraps
 from itertools import groupby
 
 from django.conf import settings
-from django.db.models import Prefetch, Sum
+from django.db.models import Prefetch, Sum, Exists, OuterRef
 from django.utils.functional import cached_property
 from django.utils.timezone import now
 from django_scopes import scopes_disabled
 
 from pretix.base.i18n import language
 from pretix.base.models import (
-    CartPosition, InvoiceAddress, OrderPosition, QuestionAnswer,
+    CartPosition, InvoiceAddress, OrderPosition, QuestionAnswer, ItemAddOn, Question, QuestionOption,
 )
 from pretix.base.services.cart import get_fees
 from pretix.helpers.cookies import set_cookie_without_samesite
@@ -68,12 +68,15 @@ class CartMixin:
                 prefetch.append(Prefetch('answers', queryset=QuestionAnswer.objects.prefetch_related('options')))
 
             cartpos = queryset.order_by(
-                'item__category__position', 'item__category_id', 'item__position', 'item__name', 'variation__value'
+                'item__category__position', 'item__category_id', 'item__position', 'item__name',
+                'variation__value'
             ).select_related(
-                'item', 'variation', 'addon_to', 'subevent', 'subevent__event', 'subevent__event__organizer', 'seat'
+                'item', 'variation', 'addon_to', 'subevent', 'subevent__event',
+                'subevent__event__organizer', 'seat'
             ).prefetch_related(
                 *prefetch
             )
+
         else:
             cartpos = self.positions
 
@@ -123,7 +126,7 @@ class CartMixin:
                     or pos.pk in has_addons \
                     or pos.addon_to_id \
                     or pos.item.issue_giftcard \
-                    or (answers and (has_attendee_data or pos.item.questions.exists())):
+                    or (answers and (has_attendee_data or bool(pos.item.questions.all()))):  # do not use .exists() to re-use prefetch cache
                 return (
                     # standalone positions are grouped by main product position id, addons below them also sorted by position id
                     i, addon_penalty, pos.pk,
@@ -147,7 +150,8 @@ class CartMixin:
             group.total = group.count * group.price
             group.net_total = group.count * group.net_price
             group.has_questions = answers and k[0] != ""
-            group.tax_rule = group.item.tax_rule
+            if not hasattr(group, 'tax_rule'):
+                group.tax_rule = group.item.tax_rule
 
             group.bundle_sum = group.price + sum(a.price for a in has_addons[group.pk])
             group.bundle_sum_net = group.net_price + sum(a.net_price for a in has_addons[group.pk])
@@ -214,6 +218,8 @@ def cart_exists(request):
 
 def get_cart(request):
     from pretix.presale.views.cart import get_or_create_cart_id
+    qqs = request.event.questions.all()
+    qqs = qqs.filter(ask_during_checkin=False, hidden=False)
 
     if not hasattr(request, '_cart_cache'):
         cart_id = get_or_create_cart_id(request, create=False)
@@ -222,11 +228,36 @@ def get_cart(request):
         else:
             request._cart_cache = CartPosition.objects.filter(
                 cart_id=cart_id, event=request.event
+            ).annotate(
+                has_addon_choices=Exists(
+                    ItemAddOn.objects.filter(
+                        base_item_id=OuterRef('item_id')
+                    )
+                )
             ).order_by(
-                'item', 'variation'
+                'item__category__position', 'item__category_id', 'item__position', 'item__name', 'variation__value'
             ).select_related(
                 'item', 'variation', 'subevent', 'subevent__event', 'subevent__event__organizer',
                 'item__tax_rule', 'addon_to'
+            ).select_related(
+                'addon_to'
+            ).prefetch_related(
+                'addons', 'addons__item', 'addons__variation',
+                Prefetch('answers',
+                         QuestionAnswer.objects.prefetch_related('options'),
+                         to_attr='answerlist'),
+                Prefetch('item__questions',
+                         qqs.prefetch_related(
+                             Prefetch('options', QuestionOption.objects.prefetch_related(Prefetch(
+                                 # This prefetch statement is utter bullshit, but it actually prevents Django from doing
+                                 # a lot of queries since ModelChoiceIterator stops trying to be clever once we have
+                                 # a prefetch lookup on this query...
+                                 'question',
+                                 Question.objects.none(),
+                                 to_attr='dummy'
+                             )))
+                         ).select_related('dependency_question'),
+                         to_attr='questions_to_ask')
             )
             for cp in request._cart_cache:
                 cp.event = request.event  # Populate field with known value to save queries

src/pretix/presale/views/event.py

@@ -408,7 +408,7 @@ class EventIndex(EventViewMixin, EventListMixin, CartMixin, TemplateView):
         context['ev'] = self.subevent or self.request.event
         context['subevent'] = self.subevent
         context['cart'] = self.get_cart()
-        context['has_addon_choices'] = get_cart(self.request).filter(item__addons__isnull=False).exists()
+        context['has_addon_choices'] = any(cp.has_addon_choices for cp in get_cart(self.request))\
 
         if self.subevent:
             context['frontpage_text'] = str(self.subevent.frontpage_text)

src/pretix/presale/views/order.py

@@ -245,6 +245,8 @@ class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TicketPageMixin,
         ).exclude(
             provider__in=('offsetting', 'reseller', 'boxoffice', 'manual')
         )
+        ctx['user_change_allowed'] = self.order.user_change_allowed
+        ctx['user_cancel_allowed'] = self.order.user_cancel_allowed
         for r in ctx['refunds']:
             if r.provider == 'giftcard':
                 gc = GiftCard.objects.get(pk=r.info_data.get('gift_card'))

src/pretix/presale/views/questions.py

@@ -1,7 +1,5 @@
-from django.db.models import Prefetch
 from django.utils.functional import cached_property
 
-from pretix.base.models import Question, QuestionAnswer, QuestionOption
 from pretix.base.views.mixins import BaseQuestionsViewMixin
 from pretix.presale.forms.checkout import QuestionsForm
 from pretix.presale.views import get_cart
@@ -13,27 +11,5 @@ class QuestionsViewMixin(BaseQuestionsViewMixin):
 
     @cached_property
     def _positions_for_questions(self):
-        qqs = self.request.event.questions.all()
-        if self.only_user_visible:
-            qqs = qqs.filter(ask_during_checkin=False, hidden=False)
-        cart = get_cart(self.request).select_related(
-            'addon_to'
-        ).prefetch_related(
-            'addons', 'addons__item', 'addons__variation',
-            Prefetch('answers',
-                     QuestionAnswer.objects.prefetch_related('options'),
-                     to_attr='answerlist'),
-            Prefetch('item__questions',
-                     qqs.prefetch_related(
-                         Prefetch('options', QuestionOption.objects.prefetch_related(Prefetch(
-                             # This prefetch statement is utter bullshit, but it actually prevents Django from doing
-                             # a lot of queries since ModelChoiceIterator stops trying to be clever once we have
-                             # a prefetch lookup on this query...
-                             'question',
-                             Question.objects.none(),
-                             to_attr='dummy'
-                         )))
-                     ).select_related('dependency_question'),
-                     to_attr='questions_to_ask')
-        )
+        cart = get_cart(self.request)
         return sorted(list(cart), key=self._keyfunc)