API: Make all mutating endpoints transactional (#6430)

All of our API endpoints that do something in the system do at least two
SQL queries, one for the actual change and one for the log entry. Often
many more. We want all of this to happen in a transaction so we know an
API call was executed or not at all, not half-way.

src/pretix/api/views/item.py

@@ -33,6 +33,7 @@
 # License for the specific language governing permissions and limitations under the License.
 
 import django_filters
+from django.db import transaction
 from django.db.models import Q
 from django.shortcuts import get_object_or_404
 from django.utils.functional import cached_property
@@ -109,6 +110,7 @@ class ItemViewSet(ConditionalListView, viewsets.ModelViewSet):
             'limit_sales_channels', 'variations__limit_sales_channels', 'program_times'
         ).all()
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -123,6 +125,7 @@ class ItemViewSet(ConditionalListView, viewsets.ModelViewSet):
         ctx['event'] = self.request.event
         return ctx
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         original_data = self.get_serializer(instance=serializer.instance).data
 
@@ -139,6 +142,7 @@ class ItemViewSet(ConditionalListView, viewsets.ModelViewSet):
             data=self.request.data
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         if not instance.allow_delete():
             raise PermissionDenied('This item cannot be deleted because it has already been ordered '
@@ -183,6 +187,7 @@ class ItemVariationViewSet(viewsets.ModelViewSet):
         ctx['event'] = self.request.event
         return ctx
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         item = self.item
         if not item.has_variations:
@@ -197,6 +202,7 @@ class ItemVariationViewSet(viewsets.ModelViewSet):
                              {'value': serializer.instance.value})
         )
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.item.log_action(
@@ -207,6 +213,7 @@ class ItemVariationViewSet(viewsets.ModelViewSet):
                              {'value': serializer.instance.value})
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         if not instance.allow_delete():
             raise PermissionDenied('This variation cannot be deleted because it has already been ordered '
@@ -249,6 +256,7 @@ class ItemBundleViewSet(viewsets.ModelViewSet):
         ctx['item'] = self.item
         return ctx
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         item = get_object_or_404(Item, pk=self.kwargs['item'], event=self.request.event)
         serializer.save(base_item=item)
@@ -259,6 +267,7 @@ class ItemBundleViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.base_item.log_action(
@@ -268,6 +277,7 @@ class ItemBundleViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         super().perform_destroy(instance)
         instance.base_item.log_action(
@@ -303,6 +313,7 @@ class ItemProgramTimeViewSet(viewsets.ModelViewSet):
         ctx['item'] = self.item
         return ctx
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         item = get_object_or_404(Item, pk=self.kwargs['item'], event=self.request.event)
         serializer.save(item=item)
@@ -313,6 +324,7 @@ class ItemProgramTimeViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.item.log_action(
@@ -322,6 +334,7 @@ class ItemProgramTimeViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         super().perform_destroy(instance)
         instance.item.log_action(
@@ -354,6 +367,7 @@ class ItemAddOnViewSet(viewsets.ModelViewSet):
         ctx['item'] = self.item
         return ctx
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         item = self.item
         category = get_object_or_404(ItemCategory, pk=self.request.data['addon_category'])
@@ -365,6 +379,7 @@ class ItemAddOnViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'ORDER': serializer.instance.position}, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.base_item.log_action(
@@ -374,6 +389,7 @@ class ItemAddOnViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'ORDER': serializer.instance.position}, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         super().perform_destroy(instance)
         instance.base_item.log_action(
@@ -403,6 +419,7 @@ class ItemCategoryViewSet(ConditionalListView, viewsets.ModelViewSet):
     def get_queryset(self):
         return self.request.event.categories.all()
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -417,6 +434,7 @@ class ItemCategoryViewSet(ConditionalListView, viewsets.ModelViewSet):
         ctx['event'] = self.request.event
         return ctx
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -426,6 +444,7 @@ class ItemCategoryViewSet(ConditionalListView, viewsets.ModelViewSet):
             data=self.request.data
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         for item in instance.items.all():
             item.category = None
@@ -458,6 +477,7 @@ class QuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
     def get_queryset(self):
         return self.request.event.questions.prefetch_related('options').all()
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -472,6 +492,7 @@ class QuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
         ctx['event'] = self.request.event
         return ctx
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -481,6 +502,7 @@ class QuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
             data=self.request.data
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         instance.log_action(
             'pretix.event.question.deleted',
@@ -509,6 +531,7 @@ class QuestionOptionViewSet(viewsets.ModelViewSet):
         ctx['question'] = get_object_or_404(Question, pk=self.kwargs['question'], event=self.request.event)
         return ctx
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         q = get_object_or_404(Question, pk=self.kwargs['question'], event=self.request.event)
         serializer.save(question=q)
@@ -519,6 +542,7 @@ class QuestionOptionViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'ORDER': serializer.instance.position}, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.question.log_action(
@@ -528,6 +552,7 @@ class QuestionOptionViewSet(viewsets.ModelViewSet):
             data=merge_dicts(self.request.data, {'ORDER': serializer.instance.position}, {'id': serializer.instance.pk})
         )
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         instance.question.log_action(
             'pretix.event.question.option.deleted',
@@ -586,6 +611,7 @@ class QuotaViewSet(ConditionalListView, viewsets.ModelViewSet):
         serializer = self.get_serializer(page, many=True)
         return self.get_paginated_response(serializer.data)
 
+    @transaction.atomic()
     def perform_create(self, serializer):
         serializer.save(event=self.request.event)
         serializer.instance.log_action(
@@ -608,6 +634,7 @@ class QuotaViewSet(ConditionalListView, viewsets.ModelViewSet):
         ctx['request'] = self.request
         return ctx
 
+    @transaction.atomic()
     def perform_update(self, serializer):
         original_data = self.get_serializer(instance=serializer.instance).data
 
@@ -663,6 +690,7 @@ class QuotaViewSet(ConditionalListView, viewsets.ModelViewSet):
                 )
         serializer.instance.rebuild_cache()
 
+    @transaction.atomic()
     def perform_destroy(self, instance):
         instance.log_action(
             'pretix.event.quota.deleted',