Add support for reserved seating (#1228)

* Initial work on seating

* Add seat guids

* Add product_list_top

* CartAdd: Ignore item when a seat is passed

* Cart display

* product_list_top → render_seating_plan

* Render seating plan in voucher redemption

* Fix failing tests

* Add tests for extending cart positions with seats

* Add subevent_forms to docs

* Update schema, migrations

* Dealing with expired orders

* steps to order change

* Change order positions

* Allow to add seats

* tests for ocm

* Fix things after rebase

* Seating plans API

* Add more tests for cart behaviour

* Widget support

* Adjust widget tests

* Re-enable CSP

* Update schema

* Api: position.seat

* Add guid to word list

* API: (sub)event.seating_plan

* Vali fixes

* Fix api

* Fix reference in test

* Fix test for real

src/pretix/base/models/vouchers.py

@@ -10,6 +10,8 @@ from django.utils.timezone import now
 from django.utils.translation import pgettext_lazy, ugettext_lazy as _
 from django_scopes import ScopedManager, scopes_disabled
 
+from pretix.base.models import SeatCategoryMapping
+
 from ..decimal import round_decimal
 from .base import LoggedModel
 from .event import Event, SubEvent
@@ -395,3 +397,11 @@ class Voucher(LoggedModel):
         """
 
         return Order.objects.filter(all_positions__voucher__in=[self]).distinct()
+
+    def seating_available(self):
+        kwargs = {}
+        if self.subevent:
+            kwargs['subevent'] = self.subevent
+        if self.quota_id:
+            return SeatCategoryMapping.objects.filter(product__quotas__pk=self.quota_id, **kwargs).exists()
+        return self.item.seat_category_mappings.filter(**kwargs).exists()