Do not CASCADE-delete vouchers when deleting items or quotas

src/pretix/base/models/items.py

@@ -174,6 +174,8 @@ def filter_available(qs, channel='web', voucher=None, allow_addons=False):
             q &= Q(pk=voucher.item_id)
         elif voucher.quota_id:
             q &= Q(quotas__in=[voucher.quota_id])
+        else:
+            return qs.none()
     if not voucher or not voucher.show_hidden_items:
         q &= Q(hide_without_voucher=False)
 
@@ -411,6 +413,7 @@ class Item(LoggedModel):
             self.event.cache.clear()
 
     def delete(self, *args, **kwargs):
+        self.vouchers.update(item=None, variation=None, quota=None)
         super().delete(*args, **kwargs)
         if self.event:
             self.event.cache.clear()
@@ -655,6 +658,7 @@ class ItemVariation(models.Model):
         return t
 
     def delete(self, *args, **kwargs):
+        self.vouchers.update(item=None, variation=None, quota=None)
         super().delete(*args, **kwargs)
         if self.item:
             self.item.event.cache.clear()
@@ -1275,6 +1279,7 @@ class Quota(LoggedModel):
         return self.name
 
     def delete(self, *args, **kwargs):
+        self.vouchers.update(item=None, variation=None, quota=None)
         super().delete(*args, **kwargs)
         if self.event:
             self.event.cache.clear()

src/pretix/base/models/vouchers.py

@@ -142,22 +142,26 @@ class Voucher(LoggedModel):
     item = models.ForeignKey(
         Item, related_name='vouchers',
         verbose_name=_("Product"),
-        null=True, blank=True, on_delete=models.CASCADE,
+        null=True, blank=True,
+        on_delete=models.PROTECT,  # We use a fake version of SET_NULL in Item.delete()
         help_text=_(
             "This product is added to the user's cart if the voucher is redeemed."
         )
     )
     variation = models.ForeignKey(
         ItemVariation, related_name='vouchers',
-        null=True, blank=True, on_delete=models.CASCADE,
+        null=True, blank=True,
+        on_delete=models.PROTECT,  # We use a fake version of SET_NULL in ItemVariation.delete() to avoid the semantic change
+                                   # that would happen if we just set variation to None
         verbose_name=_("Product variation"),
         help_text=_(
             "This variation of the product select above is being used."
         )
     )
     quota = models.ForeignKey(
-        Quota, related_name='quota',
-        null=True, blank=True, on_delete=models.CASCADE,
+        Quota, related_name='vouchers',
+        null=True, blank=True,
+        on_delete=models.PROTECT,  # We use a fake version of SET_NULL in Quota.delete()
         verbose_name=_("Quota"),
         help_text=_(
             "If enabled, the voucher is valid for any product affected by this quota."
@@ -408,4 +412,7 @@ class Voucher(LoggedModel):
             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()
+        elif self.item_id:
+            return self.item.seat_category_mappings.filter(**kwargs).exists()
+        else:
+            return False

src/pretix/control/templates/pretixcontrol/item/delete.html

@@ -17,6 +17,19 @@
 			{% csrf_token %}
             {% if possible %}
     			<p>{% blocktrans %}Are you sure you want to delete the product <strong>{{ item }}</strong>?{% endblocktrans %}</p>
+                {% if vouchers %}
+                    <div class="alert alert-warning">
+                        {% blocktrans trimmed count count=vouchers %}
+                            That will cause {{ count }} voucher to be unusable.
+                            {% plural %}
+                            That will cause {{ count }} voucher to be unusable.
+                        {% endblocktrans %}
+                        <a href="{% url "control:event.vouchers" organizer=request.organizer.slug event=request.event.slug %}?itemvar={{ item.pk }}"
+                           class="btn btn-default">
+                            {% trans "Show affected vouchers" %}
+                        </a>
+                    </div>
+                {% endif %}
             {% else %}
                 <p>{% blocktrans %}You cannot delete the product <strong>{{ item }}</strong> because it already has been ordered, but you can deactivate it.{% endblocktrans %}</p>
             {% endif %}

src/pretix/control/templates/pretixcontrol/items/quota_delete.html

@@ -3,23 +3,42 @@
 {% load bootstrap3 %}
 {% block title %}{% trans "Delete quota" %}{% endblock %}
 {% block inside %}
-	<h1>{% trans "Delete quota" %}</h1>
-	<form action="" method="post" class="form-horizontal">
-		{% csrf_token %}
-		<p>{% blocktrans %}Are you sure you want to delete the quota <strong>{{ quota }}</strong>?{% endblocktrans %}</p>
-		{% if dependent|length > 0 %}
-			<p>{% blocktrans %}The following products might be no longer available for sale:{% endblocktrans %}</p>
-			{% for item in dependent %}
-				<li><a href="{% url "control:event.item" organizer=request.event.organizer.slug event=request.event.slug item=item.pk %}">{{ item.name }}</a></li>
-			{% endfor %}
-		{% endif %}
-		<div class="form-group submit-group">
+    <h1>{% trans "Delete quota" %}</h1>
+    <form action="" method="post" class="form-horizontal">
+        {% csrf_token %}
+        <p>{% blocktrans %}Are you sure you want to delete the quota <strong>{{ quota }}</strong>?{% endblocktrans %}</p>
+        {% if dependent|length > 0 %}
+            <div class="alert alert-info">
+                <p>{% blocktrans %}The following products might be no longer available for sale:{% endblocktrans %}</p>
+                <ul>
+                    {% for item in dependent %}
+                        <li>
+                            <a href="{% url "control:event.item" organizer=request.event.organizer.slug event=request.event.slug item=item.pk %}">{{ item.name }}</a>
+                        </li>
+                    {% endfor %}
+                </ul>
+            </div>
+        {% endif %}
+        {% if vouchers %}
+            <div class="alert alert-warning">
+                {% blocktrans trimmed count count=vouchers %}
+                    That will cause {{ count }} voucher to be unusable.
+                    {% plural %}
+                    That will cause {{ count }} voucher to be unusable.
+                {% endblocktrans %}
+                <a href="{% url "control:event.vouchers" organizer=request.organizer.slug event=request.event.slug %}?itemvar=q-{{ quota.pk }}"
+                   class="btn btn-default">
+                    {% trans "Show affected vouchers" %}
+                </a>
+            </div>
+        {% endif %}
+        <div class="form-group submit-group">
             <a href="{% url "control:event.items.quotas" organizer=request.event.organizer.slug event=request.event.slug %}" class="btn btn-default btn-cancel">
                 {% trans "Cancel" %}
             </a>
             <button type="submit" class="btn btn-danger btn-save">
                 {% trans "Delete" %}
             </button>
-		</div>
-	</form>
+        </div>
+    </form>
 {% endblock %}

src/pretix/control/templates/pretixcontrol/vouchers/index.html

@@ -128,7 +128,7 @@
                                     {% if v.variation %}
                                         – {{ v.variation }}
                                     {% endif %}
-                                {% else %}
+                                {% elif v.quota %}
                                     {% blocktrans trimmed with quota=v.quota.name %}
                                         Any product in quota "{{ quota }}"
                                     {% endblocktrans %}

src/pretix/control/views/item.py

@@ -771,7 +771,8 @@ class QuotaDelete(EventPermissionRequiredMixin, DeleteView):
 
     def get_context_data(self, *args, **kwargs) -> dict:
         context = super().get_context_data(*args, **kwargs)
-        context['dependent'] = list(self.get_object().items.all())
+        context['dependent'] = list(self.object.items.all())
+        context['vouchers'] = self.object.vouchers.count()
         return context
 
     @transaction.atomic
@@ -1183,6 +1184,7 @@ class ItemDelete(EventPermissionRequiredMixin, DeleteView):
     def get_context_data(self, *args, **kwargs) -> dict:
         context = super().get_context_data(*args, **kwargs)
         context['possible'] = self.is_allowed()
+        context['vouchers'] = self.object.vouchers.count()
         return context
 
     def is_allowed(self) -> bool: