Optionally allow self-service order changes after check-in

src/pretix/base/models/orders.py

@@ -626,7 +626,10 @@ class Order(LockModel, LoggedModel):
                 has_checkin=Exists(Checkin.objects.filter(position_id=OuterRef('pk')))
             ).select_related('item').prefetch_related('issued_gift_cards')
         )
-        cancelable = all([op.item.allow_cancel and not op.has_checkin for op in positions])
+        if self.event.settings.change_allow_user_if_checked_in:
+            cancelable = all([op.item.allow_cancel for op in positions])
+        else:
+            cancelable = all([op.item.allow_cancel and not op.has_checkin for op in positions])
         if not cancelable or not positions:
             return False
         for op in positions:

src/pretix/base/services/orders.py

@@ -189,6 +189,7 @@ error_messages = {
         'min'
     ),
     'addon_no_multi': gettext_lazy('You can select every add-ons from the category %(cat)s for the product %(base)s at most once.'),
+    'addon_already_checked_in': gettext_lazy('You cannot remove the position %(addon)s since it has already been checked in.'),
 }
 
 logger = logging.getLogger(__name__)
@@ -1896,6 +1897,12 @@ class OrderChangeManager:
                     for a in current_addons[cp][k][:current_num - input_num]:
                         if a.canceled:
                             continue
+                        if a.checkins.exists():
+                            raise OrderError(
+                                error_messages['addon_already_checked_in'] % {
+                                    'addon': str(a.item.name),
+                                }
+                            )
                         self.cancel(a)
 
     def _check_seats(self):

src/pretix/base/settings.py

@@ -1484,6 +1484,19 @@ DEFAULTS = {
             label=_("Do not allow changes after"),
         )
     },
+    'change_allow_user_if_checked_in': {
+        'default': 'False',
+        'type': bool,
+        'form_class': forms.BooleanField,
+        'serializer_class': serializers.BooleanField,
+        'form_kwargs': dict(
+            label=_("Allow change even though the ticket has already been checked in"),
+            help_text=_("By default, order changes are disabled after any ticket in the order has been checked in. "
+                        "If you check this box, this requirement is lifted. It is still not possible to remove an "
+                        "add-on product that has already been checked in individually. Use with care, and preferably "
+                        "only in combination with a limitation on price changes above."),
+        )
+    },
     'change_allow_attendee': {
         'default': 'False',
         'type': bool,

src/pretix/control/forms/event.py

@@ -690,6 +690,7 @@ class CancelSettingsForm(SettingsForm):
         'change_allow_user_price',
         'change_allow_user_until',
         'change_allow_user_addons',
+        'change_allow_user_if_checked_in',
         'change_allow_attendee',
     ]
 

src/pretix/control/templates/pretixcontrol/event/cancel.html

@@ -67,6 +67,7 @@
                 {% bootstrap_field form.change_allow_user_addons layout="control" %}
                 {% bootstrap_field form.change_allow_user_until layout="control" %}
                 {% bootstrap_field form.change_allow_user_price layout="control" %}
+                {% bootstrap_field form.change_allow_user_if_checked_in layout="control" %}
                 {% bootstrap_field form.change_allow_attendee layout="control" %}
                 <div class="alert alert-info">
                     <p>

src/tests/presale/test_order_change.py

@@ -122,6 +122,25 @@ class OrderChangeVariationTest(BaseOrdersTest):
         )
         assert response.status_code == 302
 
+    def test_change_with_checkin(self):
+        with scopes_disabled():
+            shirt_pos = OrderPosition.objects.create(
+                order=self.order,
+                item=self.shirt,
+                variation=self.shirt_red,
+                price=Decimal("14"),
+            )
+            shirt_pos.checkins.create(list=self.event.checkin_lists.create(name="Test"))
+        response = self.client.get(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret)
+        )
+        assert response.status_code == 302
+        self.event.settings.change_allow_user_if_checked_in = True
+        response = self.client.get(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret)
+        )
+        assert response.status_code == 302
+
     def test_change_variation_paid(self):
         self.event.settings.change_allow_user_variation = True
         self.event.settings.change_allow_user_price = 'any'
@@ -746,6 +765,40 @@ class OrderChangeAddonsTest(BaseOrdersTest):
             self.order.refresh_from_db()
             assert self.order.total == Decimal('23.00')
 
+    def test_remove_addon_checked_in(self):
+        with scopes_disabled():
+            self.event.settings.change_allow_user_if_checked_in = True
+            op = OrderPosition.objects.create(
+                order=self.order,
+                item=self.workshop1,
+                variation=None,
+                price=Decimal("12"),
+                addon_to=self.ticket_pos,
+                attendee_name_parts={'full_name': "Peter"}
+            )
+            op.checkins.create(list=self.event.checkin_lists.create(name="Test"))
+            self.order.total += Decimal("12")
+            self.order.save()
+
+        response = self.client.get(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret)
+        )
+        assert response.status_code == 200
+        assert 'Workshop 1' in response.content.decode()
+
+        doc = BeautifulSoup(response.content.decode(), "lxml")
+        assert doc.select(f'input[name=cp_{self.ticket_pos.pk}_item_{self.workshop1.pk}]')[0].attrs['checked']
+
+        response = self.client.post(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret),
+            {
+            },
+            follow=True
+        )
+        doc = BeautifulSoup(response.content.decode(), "lxml")
+        assert 'alert-danger' in response.content.decode()
+        assert 'You cannot remove the position' in response.content.decode()
+
     def test_increase_existing_addon_free_price_net(self):
         self.event.settings.display_net_prices = True
         self.iao.multi_allowed = True