From 298c3498ae5ccb24fc9d4538ef0c3ef1214b6cf0 Mon Sep 17 00:00:00 2001
From: Kyle McCormick <kmccormick@edx.org>
Date: Wed, 18 Sep 2019 12:12:41 -0400
Subject: [PATCH] Add course_exists utility to CourseOverview class

---
 .../content/course_overviews/models.py        | 19 ++++++++++++
 .../tests/test_course_overviews.py            | 31 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/openedx/core/djangoapps/content/course_overviews/models.py b/openedx/core/djangoapps/content/course_overviews/models.py
index d8b05c8b7c..e474107948 100644
--- a/openedx/core/djangoapps/content/course_overviews/models.py
+++ b/openedx/core/djangoapps/content/course_overviews/models.py
@@ -271,6 +271,25 @@ class CourseOverview(TimeStampedModel):
             else:
                 raise cls.DoesNotExist()
 
+    @classmethod
+    def course_exists(cls, course_id):
+        """
+        Check whether a course run exists (in CourseOverviews _or_ modulestore).
+
+        Checks the CourseOverview table first.
+        If it is not there, check the modulestore.
+        Equivalent to, but more efficient than:
+            bool(CourseOverview.get_from_id(course_id))
+
+        Arguments:
+            course_id (CourseKey)
+
+        Returns: bool
+        """
+        if cls.objects.filter(id=course_id).exists():
+            return True
+        return modulestore().has_course(course_id)
+
     @classmethod
     def get_from_id(cls, course_id):
         """
diff --git a/openedx/core/djangoapps/content/course_overviews/tests/test_course_overviews.py b/openedx/core/djangoapps/content/course_overviews/tests/test_course_overviews.py
index 08dab713d4..8b903fd64d 100644
--- a/openedx/core/djangoapps/content/course_overviews/tests/test_course_overviews.py
+++ b/openedx/core/djangoapps/content/course_overviews/tests/test_course_overviews.py
@@ -322,6 +322,37 @@ class CourseOverviewTestCase(CatalogIntegrationMixin, ModuleStoreTestCase, Cache
         with self.assertRaises(CourseOverview.DoesNotExist):
             CourseOverview.get_from_id(store.make_course_key('Non', 'Existent', 'Course'))
 
+    @ddt.data(ModuleStoreEnum.Type.split, ModuleStoreEnum.Type.mongo)
+    def test_course_with_course_overview_exists(self, modulestore_type):
+        """
+        Tests that calling course_exists on an existent course
+        that is cached in CourseOverview table returns True.
+        """
+        course = CourseFactory.create(default_store=modulestore_type)
+        CourseOverview.get_from_id(course.id)  # Ensure course in cached in CourseOverviews
+        self.assertTrue(CourseOverview.objects.filter(id=course.id).exists())
+        self.assertTrue(CourseOverview.course_exists(course.id))
+
+    @ddt.data(ModuleStoreEnum.Type.split, ModuleStoreEnum.Type.mongo)
+    def test_course_without_overview_exists(self, modulestore_type):
+        """
+        Tests that calling course_exists on an existent course
+        that is NOT cached in CourseOverview table returns True.
+        """
+        course = CourseFactory.create(default_store=modulestore_type)
+        CourseOverview.objects.filter(id=course.id).delete()
+        self.assertTrue(CourseOverview.course_exists(course.id))
+        self.assertFalse(CourseOverview.objects.filter(id=course.id).exists())
+
+    @ddt.data(ModuleStoreEnum.Type.split, ModuleStoreEnum.Type.mongo)
+    def test_nonexistent_course_does_not_exists(self, modulestore_type):
+        """
+        Tests that calling course_exists on an non-existent course returns False.
+        """
+        store = modulestore()._get_modulestore_by_type(modulestore_type)  # pylint: disable=protected-access
+        course_id = store.make_course_key('Non', 'Existent', 'Course')
+        self.assertFalse(CourseOverview.course_exists(course_id))
+
     def test_get_errored_course(self):
         """
         Test that getting an ErrorDescriptor back from the module store causes