Check stock when incrementing orderproduct quantity.

src/shop/templates/shop_index.html

@@ -55,9 +55,13 @@ Shop | {{ block.super }}
             <a href="{% url 'shop:product_detail' slug=product.slug %}">
             {{ product.name }}
             </a>
-            {% if product.stock_amount and product.left_in_stock <= 10 %}
+            {% if product.stock_amount %}
             <div class="label label-danger">
-            Only {{ product.left_in_stock }} left!
+            {% if product.left_in_stock == 0 %}
+              Sold out!
+            {% elif product.left_in_stock <= 10 %}
+              Only {{ product.left_in_stock }} left!
+            {% endif %}
             </div>
             {% endif %}
           </td>

src/shop/views.py

@@ -335,6 +335,20 @@ class OrderDetailView(LoginRequiredMixin, EnsureUserOwnsOrderMixin, EnsureOrderH
                 order_product_id = str(order_product.pk)
                 if order_product_id in request.POST:
                     new_quantity = int(request.POST.get(order_product_id))
+
+                    if order_product.quantity < new_quantity:
+                        # We are incrementing and thus need to check stock
+                        incrementing_by = new_quantity - order_product.quantity
+                        if incrementing_by > order_product.product.left_in_stock:
+                            messages.error(
+                                request,
+                                "Sadly we only have {} '{}' left in stock.".format(
+                                    order_product.product.left_in_stock,
+                                    order_product.product.name,
+                                )
+                            )
+                            return super(OrderDetailView, self).get(request, *args, **kwargs)
+
                     order_product.quantity = new_quantity
                     order_product.save()
             order.customer_comment = request.POST.get('customer_comment') or ''