Refs #118 -- Asynchronous cart position removal

src/pretix/base/services/cart.py

@@ -167,6 +167,18 @@ def add_items_to_cart(event: int, items: List[Tuple[int, Optional[int], int]], c
         raise CartError(error_messages['busy'])
 
 
+def _remove_items_from_cart(event: int, items: List[Tuple[int, Optional[int], int]], cart_id: int) -> None:
+    with event.lock():
+        for item, variation, cnt in items:
+            cw = Q(cart_id=cart_id) & Q(item_id=item) & Q(event=event)
+            if variation:
+                cw &= Q(variation_id=variation)
+            else:
+                cw &= Q(variation__isnull=True)
+            for cp in CartPosition.objects.filter(cw).order_by("-price")[:cnt]:
+                cp.delete()
+
+
 def remove_items_from_cart(event: int, items: List[Tuple[int, Optional[int], int]], cart_id: int=None) -> None:
     """
     Removes a list of items from a user's cart.
@@ -175,15 +187,10 @@ def remove_items_from_cart(event: int, items: List[Tuple[int, Optional[int], int
     :param session: Session ID of a guest
     """
     event = Event.objects.get(id=event)
-
-    for item, variation, cnt in items:
-        cw = Q(cart_id=cart_id) & Q(item_id=item) & Q(event=event)
-        if variation:
-            cw &= Q(variation_id=variation)
-        else:
-            cw &= Q(variation__isnull=True)
-        for cp in CartPosition.objects.filter(cw).order_by("-price")[:cnt]:
-            cp.delete()
+    try:
+        _remove_items_from_cart(event, items, cart_id)
+    except EventLock.LockTimeoutException:
+        raise CartError(error_messages['busy'])
 
 
 if settings.HAS_CELERY:
@@ -197,4 +204,13 @@ if settings.HAS_CELERY:
         except EventLock.LockTimeoutException:
             self.retry(exc=CartError(error_messages['busy']))
 
+    @app.task(bind=True, max_retries=5, default_retry_delay=2)
+    def remove_items_from_cart_task(self, event: int, items: List[Tuple[int, Optional[int], int]], cart_id: str):
+        event = Event.objects.get(id=event)
+        try:
+            _remove_items_from_cart(event, items, cart_id)
+        except EventLock.LockTimeoutException:
+            self.retry(exc=CartError(error_messages['busy']))
+
     add_items_to_cart.task = add_items_to_cart_task
+    remove_items_from_cart.task = remove_items_from_cart_task

src/pretix/presale/templates/pretixpresale/event/fragment_cart.html

@@ -23,7 +23,7 @@
         <div class="col-md-2 col-xs-6 count">
             {% if editable %}
             <form action="{% eventurl event "presale:event.cart.remove" %}"
-                    method="post">
+                    method="post" data-asynctask>
                 {% csrf_token %}
                 {% if line.variation %}
                     <input type="hidden" name="variation_{{ line.item.id }}_{{ line.variation.id }}"

src/pretix/presale/views/cart.py

@@ -53,16 +53,30 @@ class CartActionMixin:
         return items
 
 
-class CartRemove(EventViewMixin, CartActionMixin, View):
+class CartRemove(EventViewMixin, CartActionMixin, AsyncAction, View):
+    task = remove_items_from_cart
 
-    def post(self, *args, **kwargs):
+    def get_success_message(self, value):
+        return _('Your cart has been updated.')
+
+    def get_error_message(self, exception):
+        if isinstance(exception, dict) and exception['exc_type'] == 'CartError':
+            return exception['exc_message']
+        elif isinstance(exception, CartError):
+            return str(exception)
+        return super().get_error_message(exception)
+
+    def post(self, request, *args, **kwargs):
         items = self._items_from_post_data()
-        if not items:
-            return redirect(self.get_error_url())
-
-        remove_items_from_cart(self.request.event.id, items, self.request.session.session_key)
-        messages.success(self.request, _('Your cart has been updated.'))
-        return redirect(self.get_success_url())
+        if items:
+            return self.do(self.request.event.id, items, self.request.session.session_key)
+        else:
+            if 'ajax' in self.request.GET or 'ajax' in self.request.POST:
+                return JsonResponse({
+                    'redirect': self.get_error_url()
+                })
+            else:
+                return redirect(self.get_error_url())
 
 
 class CartAdd(EventViewMixin, CartActionMixin, AsyncAction, View):