optimize db round trips, by getting the course descriptor outside of the user loop

lms/djangoapps/certificates/management/commands/ungenerated_certs.py

@@ -73,6 +73,9 @@ class Command(BaseCommand):
                     ended_courses.append(course_id)
 
         for course_id in ended_courses:
+            # prefetch all chapters/sequentials by saying depth=2
+            course = modulestore().get_instance(course_id, CourseDescriptor.id_to_location(course_id), depth=2)
+
             print "Fetching enrolled students for {0}".format(course_id)
             enrolled_students = User.objects.filter(
                 courseenrollment__course_id=course_id).prefetch_related(
@@ -99,6 +102,6 @@ class Command(BaseCommand):
                         student, course_id)['status'] in valid_statuses:
                     if not options['noop']:
                         # Add the certificate request to the queue
-                        ret = xq.add_cert(student, course_id)
+                        ret = xq.add_cert(student, course_id, course=course)
                         if ret == 'generating':
                             print '{0} - {1}'.format(student, ret)

lms/djangoapps/certificates/queue.py

@@ -115,7 +115,7 @@ class XQueueCertInterface(object):
 
         raise NotImplementedError
 
-    def add_cert(self, student, course_id):
+    def add_cert(self, student, course_id, course=None):
         """
 
         Arguments:
@@ -151,9 +151,12 @@ class XQueueCertInterface(object):
 
         if cert_status in VALID_STATUSES:
             # grade the student
-            course = courses.get_course_by_id(course_id)
-            profile = UserProfile.objects.get(user=student)
 
+            # re-use the course passed in optionally so we don't have to re-fetch everything
+            # for every student
+            if course is None:
+                course = courses.get_course_by_id(course_id)
+            profile = UserProfile.objects.get(user=student)
 
             cert, created = GeneratedCertificate.objects.get_or_create(
                    user=student, course_id=course_id)