Orders API: Reduce query load imposed by ?pdf_data=true by multiple orders of magnitude

src/pretix/api/serializers/order.py

@@ -129,12 +129,19 @@ class PdfDataSerializer(serializers.Field):
         res = {}
 
         ev = instance.subevent or instance.order.event
+        # This needs to have some extra performance improvements to avoid creating hundreds of queries when
+        # we serialize a list.
 
-        pdfvars = get_variables(instance.order.event)
-        for k, f in pdfvars.items():
+        if 'vars' not in self.context:
+            self.context['vars'] = get_variables(self.context['request'].event)
+
+        for k, f in self.context['vars'].items():
             res[k] = f['evaluate'](instance, instance.order, ev)
 
-        for k, v in ev.meta_data.items():
+        if not hasattr(ev, '_cached_meta_data'):
+            ev._cached_meta_data = ev.meta_data
+
+        for k, v in ev._cached_meta_data.items():
             res['meta:' + k] = v
 
         return res

src/pretix/api/views/order.py

@@ -3,7 +3,7 @@ import datetime
 import django_filters
 import pytz
 from django.db import transaction
-from django.db.models import Q
+from django.db.models import Prefetch, Q
 from django.db.models.functions import Concat
 from django.http import FileResponse
 from django.shortcuts import get_object_or_404
@@ -72,13 +72,34 @@ class OrderViewSet(CreateModelMixin, viewsets.ReadOnlyModelViewSet):
         return ctx
 
     def get_queryset(self):
-        return self.request.event.orders.prefetch_related(
-            'positions', 'positions__checkins', 'positions__item', 'positions__answers', 'positions__answers__options',
-            'positions__answers__question', 'fees', 'payments', 'refunds', 'refunds__payment'
+        qs = self.request.event.orders.prefetch_related(
+            'fees', 'payments', 'refunds', 'refunds__payment'
         ).select_related(
             'invoice_address'
         )
 
+        if self.request.query_params.get('pdf_data', 'false') == 'true':
+            qs = qs.prefetch_related(
+                Prefetch(
+                    'positions',
+                    OrderPosition.objects.all().prefetch_related(
+                        'checkins', 'item', 'variation', 'answers', 'answers__options', 'answers__question',
+                        Prefetch('addons', OrderPosition.objects.select_related('item', 'variation'))
+                    )
+                )
+            )
+        else:
+            qs = qs.prefetch_related(
+                Prefetch(
+                    'positions',
+                    OrderPosition.objects.all().prefetch_related(
+                        'checkins', 'item', 'variation', 'answers', 'answers__options', 'answers__question',
+                    )
+                )
+            )
+
+        return qs
+
     def _get_output_provider(self, identifier):
         responses = register_ticket_outputs.send(self.request.event)
         for receiver, response in responses:

src/pretix/base/pdf.py

@@ -161,7 +161,10 @@ DEFAULT_VARIABLES = OrderedDict((
         "editor_sample": _("Addon 1\nAddon 2"),
         "evaluate": lambda op, order, ev: "<br/>".join([
             '{} - {}'.format(p.item, p.variation) if p.variation else str(p.item)
-            for p in op.addons.select_related('item', 'variation')
+            for p in (
+                op.addons.all() if 'addons' in op._prefetched_objects_cache
+                else op.addons.select_related('item', 'variation')
+            )
         ])
     }),
     ("organizer", {

src/pretix/plugins/ticketoutputpdf/signals.py

@@ -36,10 +36,15 @@ def register_data(sender, **kwargs):
 
 def get_answer(op, order, event, question_id):
     try:
-        a = op.answers.get(question_id=question_id)
+        if 'answers' in op._prefetched_objects_cache:
+            a = [a for a in op.answers.all() if a.question_id == question_id][0]
+        else:
+            a = op.answers.get(question_id=question_id)
         return str(a).replace("\n", "<br/>\n")
     except QuestionAnswer.DoesNotExist:
         return ""
+    except IndexError:
+        return ""
 
 
 @receiver(layout_text_variables, dispatch_uid="pretix_ticketoutputpdf_layout_text_variables_questions")