Voucher creation: Auto-select products based on seat

src/pretix/api/serializers/voucher.py

@@ -78,7 +78,7 @@ class VoucherSerializer(I18nAwareModelSerializer):
 
         if full_data.get('seat'):
             data['seat'] = Voucher.clean_seat_id(
-                full_data, full_data.get('item'), self.context.get('event'),
+                full_data, full_data.get('item'), full_data.get('quota'), self.context.get('event'),
                 self.instance.pk if self.instance else None
             )
 

src/pretix/base/models/vouchers.py

@@ -217,11 +217,12 @@ class Voucher(LoggedModel):
             self.event,
             self.quota,
             self.item,
-            self.variation
+            self.variation,
+            seats_given=bool(self.seat)
         )
 
     @staticmethod
-    def clean_item_properties(data, event, quota, item, variation):
+    def clean_item_properties(data, event, quota, item, variation, seats_given=False):
         if quota:
             if quota.event != event:
                 raise ValidationError(_('You cannot select a quota that belongs to a different event.'))
@@ -240,7 +241,7 @@ class Voucher(LoggedModel):
                                         'Otherwise it might be unclear which quotas to block.'))
             if item.category and item.category.is_addon:
                 raise ValidationError(_('It is currently not possible to create vouchers for add-on products.'))
-        else:
+        elif not seats_given:
             raise ValidationError(_('You need to specify either a quota or a product.'))
 
     @staticmethod
@@ -342,14 +343,18 @@ class Voucher(LoggedModel):
             raise ValidationError(_('A voucher with this code already exists.'))
 
     @staticmethod
-    def clean_seat_id(data, item, event, pk):
+    def clean_seat_id(data, item, quota, event, pk):
         try:
             if event.has_subevents:
                 if not data.get('subevent'):
                     raise ValidationError(_('You need to choose a date if you select a seat.'))
-                seat = event.seats.get(seat_guid=data.get('seat'), subevent=data.get('subevent'))
+                seat = event.seats.select_related('product').get(
+                    seat_guid=data.get('seat'), subevent=data.get('subevent')
+                )
             else:
-                seat = event.seats.get(seat_guid=data.get('seat'))
+                seat = event.seats.select_related('product').get(
+                    seat_guid=data.get('seat')
+                )
         except Seat.DoesNotExist:
             raise ValidationError(_('The specified seat ID "{id}" does not exist for this event.').format(
                 id=data.get('seat')))
@@ -359,13 +364,13 @@ class Voucher(LoggedModel):
                                     'different voucher).').format(
                 id=seat.seat_guid))
 
-        if not item:
+        if quota:
             raise ValidationError(_('You need to choose a specific product if you select a seat.'))
 
         if data.get('max_usages', 1) > 1:
             raise ValidationError(_('Seat-specific vouchers can only be used once.'))
 
-        if seat.product != item:
+        if item and seat.product != item:
             raise ValidationError(_('You need to choose the product "{prod}" for this seat.').format(prod=seat.product))
 
         if not seat.is_available(ignore_voucher_id=pk):

src/pretix/control/forms/vouchers.py

@@ -113,7 +113,6 @@ class VoucherForm(I18nModelForm):
             }
         )
         self.fields['itemvar'].widget.choices = self.fields['itemvar'].choices
-        self.fields['itemvar'].required = True
 
         if self.instance.event.seating_plan or self.instance.event.subevents.filter(seating_plan__isnull=False).exists():
             self.fields['seat'] = forms.CharField(
@@ -124,11 +123,14 @@ class VoucherForm(I18nModelForm):
                 initial=self.instance.seat.seat_guid if self.instance.seat else '',
                 help_text=str(self.instance.seat) if self.instance.seat else '',
             )
+            self.fields['itemvar'].required = False
+        else:
+            self.fields['itemvar'].required = True
 
     def clean(self):
         data = super().clean()
 
-        if not self._errors:
+        if not self._errors and self.data.get('itemvar'):
             try:
                 itemid = quotaid = None
                 iv = self.data.get('itemvar', '')
@@ -162,7 +164,8 @@ class VoucherForm(I18nModelForm):
 
         Voucher.clean_item_properties(
             data, self.instance.event,
-            self.instance.quota, self.instance.item, self.instance.variation
+            self.instance.quota, self.instance.item, self.instance.variation,
+            seats_given=data.get('seat') or data.get('seats')
         )
         if not self.instance.show_hidden_items and (
             (self.instance.quota and all(i.hide_without_voucher for i in self.instance.quota.items.all()))
@@ -190,7 +193,10 @@ class VoucherForm(I18nModelForm):
             )
         Voucher.clean_voucher_code(data, self.instance.event, self.instance.pk)
         if 'seat' in self.fields and data.get('seat'):
-            self.instance.seat = Voucher.clean_seat_id(data, self.instance.item, self.instance.event, self.instance.pk)
+            self.instance.seat = Voucher.clean_seat_id(
+                data, self.instance.item, self.instance.quota, self.instance.event, self.instance.pk
+            )
+            self.instance.item = self.instance.seat.product
 
         voucher_form_validation.send(sender=self.instance.event, form=self, data=data)
 
@@ -357,7 +363,10 @@ class VoucherBulkForm(VoucherForm):
             data['seats'] = []
             for s in seatids:
                 data['seat'] = s
-                data['seats'].append(Voucher.clean_seat_id(data, self.instance.item, self.instance.event, None))
+                data['seats'].append(Voucher.clean_seat_id(
+                    data, self.instance.item, self.instance.quota, self.instance.event, None
+                ))
+            self.instance.seat = data['seats'][0]  # Trick model-level validation
         else:
             data['seats'] = []
 
@@ -371,6 +380,7 @@ class VoucherBulkForm(VoucherForm):
             obj.code = code
             try:
                 obj.seat = self.cleaned_data['seats'].pop()
+                obj.item = obj.seat.product
             except IndexError:
                 pass
             data = dict(self.cleaned_data)