Reduce number of redundant SQL queries

src/pretix/presale/views/__init__.py

@@ -15,33 +15,24 @@ class CartMixin:
         """
         A list of this users cart position
         """
-        return list(CartPosition.objects.filter(
-            cart_id=self.request.session.session_key, event=self.request.event
-        ).order_by(
-            'item', 'variation'
-        ).select_related(
-            'item', 'variation'
-        ).prefetch_related(
-            'item__questions', 'answers'
-        ))
+        return list(get_cart(self.request))
 
     def get_cart(self, answers=False, queryset=None, payment_fee=None, payment_fee_tax_rate=None, downloads=False):
-        queryset = queryset or CartPosition.objects.filter(
-            cart_id=self.request.session.session_key, event=self.request.event
-        )
+        if queryset:
+            prefetch = []
+            if answers:
+                prefetch.append('item__questions')
+                prefetch.append('answers')
 
-        prefetch = []
-        if answers:
-            prefetch.append('item__questions')
-            prefetch.append('answers')
-
-        cartpos = queryset.order_by(
-            'item', 'variation'
-        ).select_related(
-            'item', 'variation'
-        ).prefetch_related(
-            *prefetch
-        )
+            cartpos = queryset.order_by(
+                'item', 'variation'
+            ).select_related(
+                'item', 'variation'
+            ).prefetch_related(
+                *prefetch
+            )
+        else:
+            cartpos = self.positions
 
         # Group items of the same variation
         # We do this by list manipulations instead of a GROUP BY query, as
@@ -101,6 +92,20 @@ class CartMixin:
         return payment_fee
 
 
+def get_cart(request):
+    if not hasattr(request, '_cart_cache'):
+        request._cart_cache = CartPosition.objects.filter(
+            cart_id=request.session.session_key, event=request.event
+        ).order_by(
+            'item', 'variation'
+        ).select_related(
+            'item', 'variation'
+        ).prefetch_related(
+            'item__questions', 'answers'
+        )
+    return request._cart_cache
+
+
 class EventViewMixin:
     def get_context_data(self, **kwargs):
         context = super().get_context_data(**kwargs)

src/pretix/presale/views/checkout.py

@@ -4,15 +4,17 @@ from django.shortcuts import redirect
 from django.utils.translation import ugettext_lazy as _
 from django.views.generic import View
 
+from pretix.base.models import CartPosition
 from pretix.multidomain.urlreverse import eventreverse
 from pretix.presale.checkoutflow import get_checkout_flow
-from pretix.presale.views import CartMixin
 
 
-class CheckoutView(CartMixin, View):
+class CheckoutView(View):
     def dispatch(self, request, *args, **kwargs):
         self.request = request
-        if not self.positions and "async_id" not in request.GET:
+        has_cart = CartPosition.objects.filter(
+            cart_id=self.request.session.session_key, event=self.request.event).exists()
+        if not has_cart and "async_id" not in request.GET:
             messages.error(request, _("Your cart is empty"))
             return redirect(eventreverse(self.request.event, 'presale:event.index'))
 

src/pretix/presale/views/event.py

@@ -1,9 +1,11 @@
 import sys
 
-from django.db.models import Count, Q
+from django.db.models import Count, Prefetch, Q
 from django.utils.timezone import now
 from django.views.generic import TemplateView
 
+from pretix.base.models import ItemVariation
+
 from . import CartMixin, EventViewMixin
 
 
@@ -21,48 +23,56 @@ def item_group_by_category(items):
     )
 
 
+def get_grouped_items(event):
+    items = event.items.all().filter(
+        Q(active=True)
+        & Q(Q(available_from__isnull=True) | Q(available_from__lte=now()))
+        & Q(Q(available_until__isnull=True) | Q(available_until__gte=now()))
+        & Q(hide_without_voucher=False)
+    ).select_related(
+        'category',  # for re-grouping
+    ).prefetch_related(
+        'quotas', 'variations__quotas', 'quotas__event',  # for .availability()
+        Prefetch('variations', to_attr='available_variations',
+                 queryset=ItemVariation.objects.filter(active=True, quotas__isnull=False).distinct()),
+    ).annotate(
+        quotac=Count('quotas'),
+        has_variations=Count('variations')
+    ).filter(
+        quotac__gt=0
+    ).order_by('category__position', 'category_id', 'position', 'name')
+    display_add_to_cart = False
+    for item in items:
+        if not item.has_variations:
+            item.cached_availability = list(item.check_quotas())
+            item.order_max = min(item.cached_availability[1]
+                                 if item.cached_availability[1] is not None else sys.maxsize,
+                                 int(event.settings.max_items_per_order))
+            item.price = item.default_price
+            display_add_to_cart = display_add_to_cart or item.order_max > 0
+        else:
+            for var in item.available_variations:
+                var.cached_availability = list(var.check_quotas())
+                var.order_max = min(var.cached_availability[1]
+                                    if var.cached_availability[1] is not None else sys.maxsize,
+                                    int(event.settings.max_items_per_order))
+                display_add_to_cart = display_add_to_cart or var.order_max > 0
+                var.price = var.default_price if var.default_price is not None else item.default_price
+            if len(item.available_variations) > 0:
+                item.min_price = min([v.price for v in item.available_variations])
+                item.max_price = max([v.price for v in item.available_variations])
+
+    items = [item for item in items if len(item.available_variations) > 0 or not item.has_variations]
+    return items, display_add_to_cart
+
+
 class EventIndex(EventViewMixin, CartMixin, TemplateView):
     template_name = "pretixpresale/event/index.html"
 
     def get_context_data(self, **kwargs):
         context = super().get_context_data(**kwargs)
         # Fetch all items
-        items = self.request.event.items.all().filter(
-            Q(active=True)
-            & Q(Q(available_from__isnull=True) | Q(available_from__lte=now()))
-            & Q(Q(available_until__isnull=True) | Q(available_until__gte=now()))
-            & Q(hide_without_voucher=False)
-        ).select_related(
-            'category',  # for re-grouping
-        ).prefetch_related(
-            'quotas', 'variations__quotas', 'quotas__event'  # for .availability()
-        ).annotate(quotac=Count('quotas')).filter(
-            quotac__gt=0
-        ).order_by('category__position', 'category_id', 'position', 'name')
-        display_add_to_cart = False
-        for item in items:
-            item.available_variations = list(item.variations.filter(active=True, quotas__isnull=False).distinct())
-            item.has_variations = item.variations.exists()
-            if not item.has_variations:
-                item.cached_availability = list(item.check_quotas())
-                item.order_max = min(item.cached_availability[1]
-                                     if item.cached_availability[1] is not None else sys.maxsize,
-                                     int(self.request.event.settings.max_items_per_order))
-                item.price = item.default_price
-                display_add_to_cart = display_add_to_cart or item.order_max > 0
-            else:
-                for var in item.available_variations:
-                    var.cached_availability = list(var.check_quotas())
-                    var.order_max = min(var.cached_availability[1]
-                                        if var.cached_availability[1] is not None else sys.maxsize,
-                                        int(self.request.event.settings.max_items_per_order))
-                    display_add_to_cart = display_add_to_cart or var.order_max > 0
-                    var.price = var.default_price if var.default_price is not None else item.default_price
-                if len(item.available_variations) > 0:
-                    item.min_price = min([v.price for v in item.available_variations])
-                    item.max_price = max([v.price for v in item.available_variations])
-
-        items = [item for item in items if len(item.available_variations) > 0 or not item.has_variations]
+        items, display_add_to_cart = get_grouped_items(self.request.event)
 
         # Regroup those by category
         context['items_by_category'] = item_group_by_category(items)

src/pretix/presale/views/order.py

@@ -34,7 +34,7 @@ class OrderDetailMixin:
     @cached_property
     def order(self):
         try:
-            order = Order.objects.get(event=self.request.event, code=self.kwargs['order'])
+            order = self.request.event.orders.get(code=self.kwargs['order'])
             if order.secret.lower() == self.kwargs['secret'].lower():
                 return order
             else: