Fix for SOL-475 (double exam grader bug)

- Remove grader(s) upon deletion of existing entrance exam
- Remove grader(s) upon addition of new entrance exam

cms/djangoapps/contentstore/views/entrance_exam.py

@@ -10,7 +10,7 @@ from django.contrib.auth.decorators import login_required
 from django_future.csrf import ensure_csrf_cookie
 from django.http import HttpResponse, HttpResponseBadRequest
 
-from contentstore.views.helpers import create_xblock
+from contentstore.views.helpers import create_xblock, remove_entrance_exam_graders
 from contentstore.views.item import delete_item
 from models.settings.course_metadata import CourseMetadata
 from opaque_keys.edx.keys import CourseKey, UsageKey
@@ -270,6 +270,9 @@ def _delete_entrance_exam(request, course_key):
         }
         CourseMetadata.update_from_dict(metadata, course, request.user)
 
+        # Clean up any pre-existing entrance exam graders
+        remove_entrance_exam_graders(course_key, request.user)
+
     return HttpResponse(status=204)
 
 

cms/djangoapps/contentstore/views/helpers.py

@@ -25,6 +25,17 @@ from models.settings.course_grading import CourseGradingModel
 
 __all__ = ['edge', 'event', 'landing']
 
+# Note: Grader types are used throughout the platform but most usages are simply in-line
+# strings.  In addition, new grader types can be defined on the fly anytime one is needed
+# (because they're just strings). This dict is an attempt to constrain the sprawl in Studio.
+GRADER_TYPES = {
+    "HOMEWORK": "Homework",
+    "LAB": "Lab",
+    "ENTRANCE_EXAM": "Entrance Exam",
+    "MIDTERM_EXAM": "Midterm Exam",
+    "FINAL_EXAM": "Final Exam"
+}
+
 
 # points to the temporary course landing page with log in and sign up
 def landing(request, org, course, coursename):
@@ -173,6 +184,18 @@ def usage_key_with_run(usage_key_string):
     return usage_key
 
 
+def remove_entrance_exam_graders(course_key, user):
+    """
+    Removes existing entrance exam graders attached to the specified course
+    Typically used when adding/removing an entrance exam.
+    """
+    grading_model = CourseGradingModel.fetch(course_key)
+    graders = grading_model.graders
+    for i, grader in enumerate(graders):
+        if grader['type'] == GRADER_TYPES['ENTRANCE_EXAM']:
+            CourseGradingModel.delete_grader(course_key, i, user)
+
+
 def create_xblock(parent_locator, user, category, display_name, boilerplate=None, is_entrance_exam=False):
     """
     Performs the actual grunt work of creating items/xblocks -- knows nothing about requests, views, etc.
@@ -228,11 +251,14 @@ def create_xblock(parent_locator, user, category, display_name, boilerplate=None
 
         # Entrance Exams: Grader assignment
         if settings.FEATURES.get('ENTRANCE_EXAMS', False):
-            course = store.get_course(usage_key.course_key)
+            course_key = usage_key.course_key
+            course = store.get_course(course_key)
             if hasattr(course, 'entrance_exam_enabled') and course.entrance_exam_enabled:
                 if category == 'sequential' and parent_locator == course.entrance_exam_id:
+                    # Clean up any pre-existing entrance exam graders
+                    remove_entrance_exam_graders(course_key, user)
                     grader = {
-                        "type": "Entrance Exam",
+                        "type": GRADER_TYPES['ENTRANCE_EXAM'],
                         "min_count": 0,
                         "drop_count": 0,
                         "short_label": "Entrance",

cms/djangoapps/contentstore/views/tests/test_entrance_exam.py

@@ -11,6 +11,7 @@ from django.test.client import RequestFactory
 from contentstore.tests.utils import AjaxEnabledTestClient, CourseTestCase
 from contentstore.utils import reverse_url
 from contentstore.views.entrance_exam import create_entrance_exam, update_entrance_exam, delete_entrance_exam
+from contentstore.views.helpers import GRADER_TYPES
 from models.settings.course_grading import CourseGradingModel
 from models.settings.course_metadata import CourseMetadata
 from opaque_keys.edx.keys import UsageKey
@@ -84,7 +85,7 @@ class EntranceExamHandlerTests(CourseTestCase):
             seq_locator_string = json.loads(resp.content).get('locator')
             seq_locator = UsageKey.from_string(seq_locator_string)
             section_grader_type = CourseGradingModel.get_section_grader_type(seq_locator)
-            self.assertEqual('Entrance Exam', section_grader_type['graderType'])
+            self.assertEqual(GRADER_TYPES['ENTRANCE_EXAM'], section_grader_type['graderType'])
 
         def test_contentstore_views_entrance_exam_get(self):
             """
@@ -140,6 +141,14 @@ class EntranceExamHandlerTests(CourseTestCase):
             resp = self.client.get(self.exam_url)
             self.assertEqual(resp.status_code, 200)
 
+            # Confirm that we have only one Entrance Exam grader after re-adding the exam (validates SOL-475)
+            graders = CourseGradingModel.fetch(self.course_key).graders
+            count = 0
+            for grader in graders:
+                if grader['type'] == GRADER_TYPES['ENTRANCE_EXAM']:
+                    count += 1
+            self.assertEqual(count, 1)
+
         def test_contentstore_views_entrance_exam_delete_bogus_course(self):
             """
             Unit Test: test_contentstore_views_entrance_exam_delete_bogus_course