Seat-specific vouchers (#1486)

* Basic functionality

* API

* Do not delete seats with vouchers

* Show seat in list of seats

* Validate availability of seats

* Fix invalid logic in Seat.is_available

* Show voucher name in edit form

src/pretix/api/serializers/voucher.py

@@ -2,15 +2,23 @@ from rest_framework import serializers
 from rest_framework.exceptions import ValidationError
 
 from pretix.api.serializers.i18n import I18nAwareModelSerializer
-from pretix.base.models import Voucher
+from pretix.base.models import Seat, Voucher
 
 
 class VoucherListSerializer(serializers.ListSerializer):
     def create(self, validated_data):
         codes = set()
+        seats = set()
         errs = []
         err = False
         for voucher_data in validated_data:
+            if voucher_data.get('seat') and (voucher_data.get('seat'), voucher_data.get('subevent')) in seats:
+                err = True
+                errs.append({'code': ['Duplicate seat ID in request.']})
+                continue
+            else:
+                seats.add((voucher_data.get('seat'), voucher_data.get('subevent')))
+
             if voucher_data['code'] in codes:
                 err = True
                 errs.append({'code': ['Duplicate voucher code in request.']})
@@ -22,12 +30,19 @@ class VoucherListSerializer(serializers.ListSerializer):
         return super().create(validated_data)
 
 
+class SeatGuidField(serializers.CharField):
+    def to_representation(self, val: Seat):
+        return val.seat_guid
+
+
 class VoucherSerializer(I18nAwareModelSerializer):
+    seat = SeatGuidField(allow_null=True, required=False)
+
     class Meta:
         model = Voucher
         fields = ('id', 'code', 'max_usages', 'redeemed', 'valid_until', 'block_quota',
                   'allow_ignore_quota', 'price_mode', 'value', 'item', 'variation', 'quota',
-                  'tag', 'comment', 'subevent', 'show_hidden_items')
+                  'tag', 'comment', 'subevent', 'show_hidden_items', 'seat')
         read_only_fields = ('id', 'redeemed')
         list_serializer_class = VoucherListSerializer
 
@@ -61,4 +76,10 @@ class VoucherSerializer(I18nAwareModelSerializer):
             )
         Voucher.clean_voucher_code(full_data, self.context.get('event'), self.instance.pk if self.instance else None)
 
+        if full_data.get('seat'):
+            data['seat'] = Voucher.clean_seat_id(
+                full_data, full_data.get('item'), self.context.get('event'),
+                self.instance.pk if self.instance else None
+            )
+
         return data

src/pretix/api/views/voucher.py

@@ -45,7 +45,7 @@ class VoucherViewSet(viewsets.ModelViewSet):
     write_permission = 'can_change_vouchers'
 
     def get_queryset(self):
-        return self.request.event.vouchers.all()
+        return self.request.event.vouchers.select_related('seat').all()
 
     def _predict_quota_check(self, data, instance):
         # This method predicts if Voucher.clean_quota_needs_checking