Reduce number of redundant SQL queries

src/pretix/presale/checkoutflow.py

@@ -91,14 +91,16 @@ class BaseCheckoutFlowStep:
 
     @cached_property
     def invoice_address(self):
-        iapk = self.cart_session.get('invoice_address')
-        if not iapk:
-            return InvoiceAddress()
-
-        try:
-            return InvoiceAddress.objects.get(pk=iapk, order__isnull=True)
-        except InvoiceAddress.DoesNotExist:
-            return InvoiceAddress()
+        if not hasattr(self.request, '_checkout_flow_invoice_address'):
+            iapk = self.cart_session.get('invoice_address')
+            if not iapk:
+                self.request._checkout_flow_invoice_address = InvoiceAddress()
+            else:
+                try:
+                    self.request._checkout_flow_invoice_address = InvoiceAddress.objects.get(pk=iapk, order__isnull=True)
+                except InvoiceAddress.DoesNotExist:
+                    self.request._checkout_flow_invoice_address = InvoiceAddress()
+        return self.request._checkout_flow_invoice_address
 
 
 def get_checkout_flow(event):
@@ -160,7 +162,9 @@ class AddOnsStep(CartMixin, AsyncAction, TemplateFlowStep):
     requires_valid_cart = False
 
     def is_applicable(self, request):
-        return get_cart(request).filter(item__addons__isnull=False).exists()
+        if not hasattr(request, '_checkoutflow_addons_applicable'):
+            request._checkoutflow_addons_applicable = get_cart(request).filter(item__addons__isnull=False).exists()
+        return request._checkoutflow_addons_applicable
 
     def is_completed(self, request, warn=False):
         for cartpos in get_cart(request).filter(addon_to__isnull=True).prefetch_related(

src/pretix/presale/views/__init__.py

@@ -24,6 +24,19 @@ class CartMixin:
         from pretix.presale.views.cart import cart_session
         return cart_session(self.request)
 
+    @cached_property
+    def invoice_address(self):
+        if not hasattr(self.request, '_checkout_flow_invoice_address'):
+            iapk = self.cart_session.get('invoice_address')
+            if not iapk:
+                self.request._checkout_flow_invoice_address = InvoiceAddress()
+            else:
+                try:
+                    self.request._checkout_flow_invoice_address = InvoiceAddress.objects.get(pk=iapk, order__isnull=True)
+                except InvoiceAddress.DoesNotExist:
+                    self.request._checkout_flow_invoice_address = InvoiceAddress()
+        return self.request._checkout_flow_invoice_address
+
     def get_cart(self, answers=False, queryset=None, order=None, downloads=False):
         if queryset:
             prefetch = []
@@ -107,15 +120,7 @@ class CartMixin:
         if order:
             fees = order.fees.all()
         else:
-            iapk = self.cart_session.get('invoice_address')
-            ia = None
-            if iapk:
-                try:
-                    ia = InvoiceAddress.objects.get(pk=iapk, order__isnull=True)
-                except InvoiceAddress.DoesNotExist:
-                    pass
-
-            fees = get_fees(self.request.event, self.request, total, ia, self.cart_session.get('payment'))
+            fees = get_fees(self.request.event, self.request, total, self.invoice_address, self.cart_session.get('payment'))
 
         total += sum([f.value for f in fees])
         net_total += sum([f.net_value for f in fees])

src/pretix/presale/views/checkout.py

@@ -4,23 +4,19 @@ 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.base.services.cart import CartError
 from pretix.base.signals import validate_cart
 from pretix.multidomain.urlreverse import eventreverse
 from pretix.presale.checkoutflow import get_checkout_flow
-from pretix.presale.views.cart import get_or_create_cart_id
+from pretix.presale.views import get_cart
 
 
 class CheckoutView(View):
     def dispatch(self, request, *args, **kwargs):
 
         self.request = request
-        cart_pos = CartPosition.objects.filter(
-            cart_id=get_or_create_cart_id(request), event=self.request.event
-        )
 
-        if not cart_pos.exists() and "async_id" not in request.GET:
+        if not get_cart(request) and "async_id" not in request.GET:
             messages.error(request, _("Your cart is empty"))
             return redirect(eventreverse(self.request.event, 'presale:event.index'))
 
@@ -30,7 +26,7 @@ class CheckoutView(View):
 
         cart_error = None
         try:
-            validate_cart.send(sender=self.request.event, positions=cart_pos)
+            validate_cart.send(sender=self.request.event, positions=get_cart(request))
         except CartError as e:
             cart_error = e