Reduce course run view's query count

Prefetching of course run video image, course level type, and program excluded runs further reduces the number of queries required to service requests for course runs.

course_discovery/apps/api/serializers.py

@@ -429,7 +429,9 @@ class CourseRunSerializer(MinimalCourseRunSerializer):
         queryset = super().prefetch_queryset(queryset=queryset)
 
         return queryset.select_related('language', 'video').prefetch_related(
+            'course__level_type',
             'transcript_languages',
+            'video__image',
             Prefetch('staff', queryset=PersonSerializer.prefetch_queryset()),
         )
 
@@ -453,7 +455,7 @@ class CourseRunWithProgramsSerializer(CourseRunSerializer):
     def prefetch_queryset(cls, queryset=None):
         queryset = super().prefetch_queryset(queryset=queryset)
 
-        return queryset.prefetch_related('course__programs')
+        return queryset.prefetch_related('course__programs__excluded_course_runs')
 
     def get_programs(self, obj):
         programs = []

course_discovery/apps/api/v1/tests/test_views/test_catalogs.py

@@ -172,7 +172,7 @@ class CatalogViewSetTests(ElasticsearchTestMixin, SerializationMixin, OAuth2Mixi
                 # to be included.
                 filtered_course_run = CourseRunFactory(course=course)
 
-                with self.assertNumQueries(18):
+                with self.assertNumQueries(19):
                     response = self.client.get(url)
 
                 assert response.status_code == 200

course_discovery/apps/api/v1/tests/test_views/test_course_runs.py

@@ -51,7 +51,7 @@ class CourseRunViewSetTests(SerializationMixin, ElasticsearchTestMixin, APITestC
 
         url = reverse('api:v1:course_run-detail', kwargs={'key': self.course_run.key})
 
-        with self.assertNumQueries(10):
+        with self.assertNumQueries(11):
             response = self.client.get(url)
         assert response.status_code == 200
         assert response.data.get('programs') == []
@@ -133,7 +133,7 @@ class CourseRunViewSetTests(SerializationMixin, ElasticsearchTestMixin, APITestC
         """ Verify the endpoint returns a list of all course runs. """
         url = reverse('api:v1:course_run-list')
 
-        with self.assertNumQueries(13):
+        with self.assertNumQueries(11):
             response = self.client.get(url)
 
         assert response.status_code == 200
@@ -146,7 +146,7 @@ class CourseRunViewSetTests(SerializationMixin, ElasticsearchTestMixin, APITestC
         """ Verify the endpoint returns a list of all course runs sorted by start date. """
         url = '{root}?ordering=start'.format(root=reverse('api:v1:course_run-list'))
 
-        with self.assertNumQueries(13):
+        with self.assertNumQueries(11):
             response = self.client.get(url)
 
         assert response.status_code == 200

course_discovery/apps/api/v1/tests/test_views/test_programs.py

@@ -64,7 +64,7 @@ class ProgramViewSetTests(SerializationMixin, APITestCase):
     def test_retrieve(self):
         """ Verify the endpoint returns the details for a single program. """
         program = self.create_program()
-        with self.assertNumQueries(39):
+        with self.assertNumQueries(41):
             response = self.assert_retrieve_success(program)
         assert response.data == self.serialize_program(program)
 
@@ -75,7 +75,7 @@ class ProgramViewSetTests(SerializationMixin, APITestCase):
         for course in course_list:
             CourseRunFactory(course=course)
         program = ProgramFactory(courses=course_list, order_courses_by_start_date=order_courses_by_start_date)
-        with self.assertNumQueries(26):
+        with self.assertNumQueries(28):
             response = self.assert_retrieve_success(program)
         assert response.data == self.serialize_program(program)
         self.assertEqual(course_list, list(program.courses.all()))  # pylint: disable=no-member