Move logic that decides whether to show shoppingcart to middleware

Middleware is a better place for this, rather than navigation.html
template

lms/djangoapps/shoppingcart/middleware.py

+"""
+This is the shoppingcart middleware class.
+Currently the only middleware is detects whether request.user has a cart that should be displayed in the
+navigation.  We want to do this in the middleware to
+1) keep database accesses out of templates (this led to a transaction bug with user email changes)
+2) because navigation.html is "called" by being included in other templates, there's no "views.py" to put this.
+"""
+from django.conf import settings
+import shoppingcart
+
+class UserHasCartMiddleware(object):
+    """
+    Detects whether request.user has a cart and sets it as part of the request
+
+    ***
+     Because this relies on request.user, it needs to enabled in settings after
+     django.contrib.auth.middleware.AuthenticationMiddleware (or equivalent)
+    ***
+    """
+    def process_request(self, request):
+        """
+        Checks if request has an authenticated user.  If so, checks if request.user has a cart that should
+        be displayed.  Anonymous users don't.
+        """
+        request.display_shopping_cart = False
+        if (request.user.is_authenticated() and  # user exists
+            settings.MITX_FEATURES.get('ENABLE_PAID_COURSE_REGISTRATION') and  # settings are set
+            settings.MITX_FEATURES.get('ENABLE_SHOPPING_CART') and
+            shoppingcart.models.Order.user_cart_has_items(request.user)):  # user's cart is non-empty
+            request.display_shopping_cart = True
+        return None
\ No newline at end of file

lms/djangoapps/shoppingcart/tests/test_middleware.py

+"""
+Unit tests for shoppingcart middleware
+"""
+from mock import patch, Mock
+from django.conf import settings
+from django.contrib.auth.models import AnonymousUser
+from django.test.utils import override_settings
+
+from courseware.tests.tests import TEST_DATA_MONGO_MODULESTORE
+from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase
+from xmodule.modulestore.tests.factories import CourseFactory
+from student.tests.factories import UserFactory
+from course_modes.models import CourseMode
+from shoppingcart.models import Order, PaidCourseRegistration
+from shoppingcart.middleware import UserHasCartMiddleware
+
+@override_settings(MODULESTORE=TEST_DATA_MONGO_MODULESTORE)
+class UserCartMiddlewareUnitTest(ModuleStoreTestCase):
+    def setUp(self):
+        self.user = UserFactory.create()
+        self.request = Mock()
+        self.mw = UserHasCartMiddleware()
+
+    def add_to_cart(self):
+        course = CourseFactory.create(org='MITx', number='999', display_name='Robot Super Course')
+        course_mode = CourseMode(course_id=course.id,
+                                 mode_slug="honor",
+                                 mode_display_name="honor cert",
+                                 min_price=40)
+        course_mode.save()
+        cart = Order.get_cart_for_user(self.user)
+        PaidCourseRegistration.add_to_order(cart, course.id)
+
+    @patch.dict(settings.MITX_FEATURES, {'ENABLE_SHOPPING_CART': False, 'ENABLE_PAID_COURSE_REGISTRATION': True})
+    def test_no_enable_shoppingcart(self):
+        """
+        Tests when MITX_FEATURES['ENABLE_SHOPPING_CART'] is not set
+        """
+        self.add_to_cart()
+        self.request.user = self.user
+        self.mw.process_request(self.request)
+        self.assertFalse(self.request.display_shopping_cart)
+
+    @patch.dict(settings.MITX_FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': False})
+    def test_no_enable_paid_course_registration(self):
+        """
+        Tests when MITX_FEATURES['ENABLE_PAID_COURSE_REGISTRATION'] is not set
+        """
+        self.add_to_cart()
+        self.request.user = self.user
+        self.mw.process_request(self.request)
+        self.assertFalse(self.request.display_shopping_cart)
+
+    @patch.dict(settings.MITX_FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
+    def test_anonymous_user(self):
+        """
+        Tests when request.user is anonymous
+        """
+        self.request.user = AnonymousUser()
+        self.mw.process_request(self.request)
+        self.assertFalse(self.request.display_shopping_cart)
+
+    @patch.dict(settings.MITX_FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
+    def test_no_items_in_cart(self):
+        """
+        Tests when request.user doesn't have a cart with items
+        """
+        self.request.user = self.user
+        self.mw.process_request(self.request)
+        self.assertFalse(self.request.display_shopping_cart)
+
+    @patch.dict(settings.MITX_FEATURES, {'ENABLE_SHOPPING_CART': True, 'ENABLE_PAID_COURSE_REGISTRATION': True})
+    def test_items_in_cart(self):
+        """
+        Tests when request.user has a cart with items
+        """
+        self.add_to_cart()
+        self.request.user = self.user
+        self.mw.process_request(self.request)
+        self.assertTrue(self.request.display_shopping_cart)

lms/envs/common.py

@@ -610,6 +610,9 @@ MIDDLEWARE_CLASSES = (
 
     # For A/B testing
     'waffle.middleware.WaffleMiddleware',
+
+    # Shoppingcart middleware (detects if request.user has a cart)
+    'shoppingcart.middleware.UserHasCartMiddleware',
 )
 
 ############################### Pipeline #######################################

lms/templates/navigation.html

@@ -9,8 +9,6 @@ from django.utils.translation import ugettext as _
 import branding
 # app that handles site status messages
 from status.status import get_site_status_msg
-# shopping cart
-import shoppingcart
 %>
 
 ## Provide a hook for themes to inject branding on top.
@@ -83,9 +81,7 @@ site_status_msg = get_site_status_msg(course_id)
         </ul>
       </li>
     </ol>
-      % if settings.MITX_FEATURES.get('ENABLE_PAID_COURSE_REGISTRATION') and \
-           settings.MITX_FEATURES.get('ENABLE_SHOPPING_CART') and \
-           shoppingcart.models.Order.user_cart_has_items(user):
+      % if getattr(request, 'display_shopping_cart', False): # see shoppingcart.middleware.UserHasCartMiddleware
         <ol class="user">
           <li class="primary">
             <a class="shopping-cart" href="${reverse('shoppingcart.views.show_cart')}">