MA-1061 Fix IntegrityError caused by race condition in CourseOverview.get_from_id

openedx/core/djangoapps/content/course_overviews/models.py

@@ -5,6 +5,7 @@ Declaration of CourseOverview model
 import json
 
 from django.db.models.fields import BooleanField, DateTimeField, DecimalField, TextField, FloatField, IntegerField
+from django.db.utils import IntegrityError
 from django.utils.translation import ugettext
 from model_utils.models import TimeStampedModel
 
@@ -172,7 +173,18 @@ class CourseOverview(TimeStampedModel):
             course = store.get_course(course_id)
             if isinstance(course, CourseDescriptor):
                 course_overview = cls._create_from_course(course)
-                course_overview.save()
+                try:
+                    course_overview.save()
+                except IntegrityError:
+                    # There is a rare race condition that will occur if
+                    # CourseOverview.get_from_id is called while a
+                    # another identical overview is already in the process
+                    # of being created.
+                    # One of the overviews will be saved normally, while the
+                    # other one will cause an IntegrityError because it tries
+                    # to save a duplicate.
+                    # (see: https://openedx.atlassian.net/browse/TNL-2854).
+                    pass
                 return course_overview
             elif course is not None:
                 raise IOError(

openedx/core/djangoapps/content/course_overviews/tests.py

@@ -4,9 +4,9 @@ Tests for course_overviews app.
 import datetime
 import ddt
 import itertools
-import pytz
 import math
 import mock
+import pytz
 
 from django.utils import timezone
 
@@ -349,3 +349,35 @@ class CourseOverviewTestCase(ModuleStoreTestCase):
             # a call to get_course.
             with check_mongo_calls_range(max_finds=max_mongo_calls, min_finds=min_mongo_calls):
                 _course_overview_2 = CourseOverview.get_from_id(course.id)
+
+    def test_course_overview_saving_race_condition(self):
+        """
+        Tests that the following scenario will not cause an unhandled exception:
+        - Multiple concurrent requests are made for the same non-existent CourseOverview.
+        - A race condition in the django ORM's save method that checks for the presence
+          of the primary key performs an Insert instead of an Update operation.
+        - An IntegrityError is raised when attempting to create duplicate entries.
+        - This should be handled gracefully in CourseOverview.get_from_id.
+
+        Created in response to https://openedx.atlassian.net/browse/MA-1061.
+        """
+        course = CourseFactory.create()
+
+        # mock the CourseOverview ORM to raise a DoesNotExist exception to force re-creation of the object
+        with mock.patch(
+            'openedx.core.djangoapps.content.course_overviews.models.CourseOverview.objects.get'
+        ) as mock_getter:
+
+            mock_getter.side_effect = CourseOverview.DoesNotExist
+
+            # mock the CourseOverview ORM to not find the primary-key to force an Insert of the object
+            with mock.patch(
+                'openedx.core.djangoapps.content.course_overviews.models.CourseOverview._get_pk_val'
+            ) as mock_get_pk_val:
+
+                mock_get_pk_val.return_value = None
+
+                # verify the CourseOverview is loaded successfully both times,
+                # including after an IntegrityError exception the 2nd time
+                for _ in range(2):
+                    self.assertIsInstance(CourseOverview.get_from_id(course.id), CourseOverview)