change the context_processor in the shopping cart to return a pointer to a…

change the context_processor in the shopping cart to return a pointer to a function so that only the templates that actually need to know if the shopping cart button should be shown will actually make the database roundtrips

lms/djangoapps/shoppingcart/context_processor.py

@@ -16,16 +16,23 @@ def user_has_cart_context_processor(request):
     be displayed.  Anonymous users don't.
     Adds `display_shopping_cart` to the context
     """
-    display_shopping_cart = (
-        # user is logged in and
-        request.user.is_authenticated() and
-        # do we have the feature turned on
-        is_shopping_cart_enabled() and
-        # user's cart has PaidCourseRegistrations
-        Order.user_cart_has_items(
-            request.user,
-            [PaidCourseRegistration, CourseRegCodeItem]
+    def should_display_shopping_cart():
+        """
+        Returns a boolean if the user has an items in a cart whereby the shopping cart should be
+        displayed to the logged in user
+        """
+        return (
+            # user is logged in and
+            request.user.is_authenticated() and
+            # do we have the feature turned on
+            is_shopping_cart_enabled() and
+            # does the user actually have a cart (optimized query to prevent creation of a cart when not needed)
+            Order.does_user_have_cart(request.user) and
+            # user's cart has PaidCourseRegistrations or CourseRegCodeItem
+            Order.user_cart_has_items(
+                request.user,
+                [PaidCourseRegistration, CourseRegCodeItem]
+            )
         )
-    )
 
-    return {'display_shopping_cart': display_shopping_cart}
+    return {'should_display_shopping_cart_func': should_display_shopping_cart}

lms/djangoapps/shoppingcart/models.py

@@ -151,6 +151,13 @@ class Order(models.Model):
         return cart_order
 
     @classmethod
+    def does_user_have_cart(cls, user):
+        """
+        Returns a boolean whether a shopping cart (Order) exists for the specified user
+        """
+        return cls.objects.filter(user=user, status='cart').exists()
+
+    @classmethod
     def user_cart_has_items(cls, user, item_types=None):
         """
         Returns true if the user (anonymous user ok) has

lms/djangoapps/shoppingcart/tests/test_context_processor.py

@@ -42,7 +42,7 @@ class UserCartContextProcessorUnitTest(ModuleStoreTestCase):
         self.add_to_cart()
         self.request.user = self.user
         context = user_has_cart_context_processor(self.request)
-        self.assertFalse(context['display_shopping_cart'])
+        self.assertFalse(context['should_display_shopping_cart_func']())
 
     @patch.dict(settings.FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': False})
     def test_no_enable_paid_course_registration(self):
@@ -52,7 +52,7 @@ class UserCartContextProcessorUnitTest(ModuleStoreTestCase):
         self.add_to_cart()
         self.request.user = self.user
         context = user_has_cart_context_processor(self.request)
-        self.assertFalse(context['display_shopping_cart'])
+        self.assertFalse(context['should_display_shopping_cart_func']())
 
     @patch.dict(settings.FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
     def test_anonymous_user(self):
@@ -61,7 +61,7 @@ class UserCartContextProcessorUnitTest(ModuleStoreTestCase):
         """
         self.request.user = AnonymousUser()
         context = user_has_cart_context_processor(self.request)
-        self.assertFalse(context['display_shopping_cart'])
+        self.assertFalse(context['should_display_shopping_cart_func']())
 
     @patch.dict(settings.FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
     def test_no_items_in_cart(self):
@@ -70,7 +70,7 @@ class UserCartContextProcessorUnitTest(ModuleStoreTestCase):
         """
         self.request.user = self.user
         context = user_has_cart_context_processor(self.request)
-        self.assertFalse(context['display_shopping_cart'])
+        self.assertFalse(context['should_display_shopping_cart_func']())
 
     @patch.dict(settings.FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
     def test_items_in_cart(self):
@@ -80,4 +80,4 @@ class UserCartContextProcessorUnitTest(ModuleStoreTestCase):
         self.add_to_cart()
         self.request.user = self.user
         context = user_has_cart_context_processor(self.request)
-        self.assertTrue(context['display_shopping_cart'])
+        self.assertTrue(context['should_display_shopping_cart_func']())

lms/templates/navigation-edx.html

@@ -85,7 +85,7 @@ site_status_msg = get_site_status_msg(course_id)
       </li>
     </ol>
 
-      % if display_shopping_cart: # see shoppingcart.context_processor.user_has_cart_context_processor
+      % if should_display_shopping_cart_func(): # see shoppingcart.context_processor.user_has_cart_context_processor
         <ol class="user">
           <li class="primary">
             <a class="shopping-cart" href="${reverse('shoppingcart.views.show_cart')}">

lms/templates/navigation.html

@@ -79,7 +79,7 @@ site_status_msg = get_site_status_msg(course_id)
         </ul>
       </li>
     </ol>
-      % if display_shopping_cart: # see shoppingcart.context_processor.user_has_cart_context_processor
+      % if should_display_shopping_cart_func(): # see shoppingcart.context_processor.user_has_cart_context_processor
         <ol class="user">
           <li class="primary">
             <a class="shopping-cart" href="${reverse('shoppingcart.views.show_cart')}">