Merge pull request #605 from MITx/feature/prefetch_user_groups

Reduce # of queries for auth checks on Progress page by prefetching user groups

lms/djangoapps/courseware/access.py

@@ -321,7 +321,7 @@ def _has_staff_access_to_location(user, location):
         return True
 
     # If not global staff, is the user in the Auth group for this class?
-    user_groups = [x[1] for x in user.groups.values_list()]
+    user_groups = [g.name for g in user.groups.all()]
     staff_group = _course_staff_group_name(location)
     if staff_group in user_groups:
         debug("Allow: user in group %s", staff_group)

lms/djangoapps/courseware/views.py

@@ -328,6 +328,10 @@ def progress(request, course_id, student_id=None):
     # NOTE: To make sure impersonation by instructor works, use
     # student instead of request.user in the rest of the function.
 
+    # The pre-fetching of groups is done to make auth checks not require an 
+    # additional DB lookup (this kills the Progress page in particular).
+    student = User.objects.prefetch_related("groups").get(id=student.id)
+
     student_module_cache = StudentModuleCache.cache_for_descriptor_descendents(
         course_id, student, course)
     course_module = get_module(student, request, course.location,