identify and prefetch N+1 queries in search/all for learner pathways (#…

…4488)

* perf: identify and prefetch N+1 queries in search/all for learner pathways

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

@@ -763,28 +763,28 @@ def test_results_include_aggregation_key(self):
         )
         assert expected == actual
 
-    @ddt.data(True, False)
-    def test_learner_pathway_feature_flag(self, include_learner_pathways):
+    @ddt.data((True, 10, 8), (False, 0, 4))
+    @ddt.unpack
+    def test_learner_pathway_feature_flag(self, include_learner_pathways, expected_result_count, expected_query_count):
         """ Verify the include_learner_pathways feature flag works as expected."""
-        LearnerPathwayStepFactory(pathway__partner=self.partner)
+        LearnerPathwayStepFactory.create_batch(10, pathway__partner=self.partner)
         pathways = LearnerPathway.objects.all()
-        assert pathways.count() == 1
+        assert pathways.count() == 10
         query = {
             'include_learner_pathways': include_learner_pathways,
         }
 
-        response = self.get_response(
-            query,
-            self.list_path
-        )
+        with self.assertNumQueries(expected_query_count):
+            response = self.get_response(query, self.list_path)
+
         assert response.status_code == 200
         response_data = response.json()
 
+        assert response_data['count'] == expected_result_count
+
         if include_learner_pathways:
-            assert response_data['count'] == 1
-            assert response_data['results'][0] == self.serialize_learner_pathway_search(pathways[0])
-        else:
-            assert response_data['count'] == 0
+            for pathway in pathways:
+                assert self.serialize_learner_pathway_search(pathway) in response.data['results']
 
 
 class LimitedAggregateSearchViewSetTests(

course_discovery/apps/course_metadata/search_indexes/documents/learner_pathway.py

@@ -1,6 +1,9 @@
 from django.conf import settings
+from django.db.models import Prefetch
 from django_elasticsearch_dsl import Index, fields
 
+from course_discovery.apps.course_metadata.choices import CourseRunStatus
+from course_discovery.apps.course_metadata.models import CourseRun
 from course_discovery.apps.learner_pathway.choices import PathwayStatus
 from course_discovery.apps.learner_pathway.models import LearnerPathway
 
@@ -50,10 +53,26 @@ def prepare_partner(self, obj):
     def prepare_published(self, obj):
         return obj.status == PathwayStatus.Active
 
-    def get_queryset(self, excluded_restriction_types=None):  # pylint: disable=unused-argument
+    def get_queryset(self, excluded_restriction_types=None):
+        if excluded_restriction_types is None:
+            excluded_restriction_types = []
+
+        course_runs = CourseRun.objects.filter(
+            status=CourseRunStatus.Published
+        ).exclude(
+            restricted_run__restriction_type__in=excluded_restriction_types
+        )
+
         return super().get_queryset().prefetch_related(
-            'steps', 'steps__learnerpathwaycourse_set', 'steps__learnerpathwayprogram_set',
-            'steps__learnerpathwayblock_set',
+            'steps',
+            Prefetch(
+                'steps__learnerpathwaycourse_set__course__course_runs',
+                queryset=course_runs
+            ),
+            Prefetch(
+                'steps__learnerpathwayprogram_set__program__courses__course_runs',
+                queryset=course_runs
+            )
         )
 
     def prepare_skill_names(self, obj):

course_discovery/apps/learner_pathway/api/serializers.py

@@ -3,8 +3,6 @@
 """
 from rest_framework import serializers
 
-from course_discovery.apps.api.utils import get_excluded_restriction_types
-from course_discovery.apps.course_metadata.choices import CourseRunStatus
 from course_discovery.apps.learner_pathway import models
 
 
@@ -20,12 +18,7 @@ class Meta:
         fields = ('key', 'course_runs')
 
     def get_course_runs(self, obj):
-        excluded_restriction_types = get_excluded_restriction_types(self.context['request'])
-        return list(obj.course.course_runs.filter(
-            status=CourseRunStatus.Published
-        ).exclude(
-            restricted_run__restriction_type__in=excluded_restriction_types
-        ).values('key'))
+        return [{'key': course_run.key} for course_run in obj.course.course_runs.all()]
 
 
 class LearnerPathwayCourseSerializer(LearnerPathwayCourseMinimalSerializer):
@@ -87,8 +80,7 @@ def get_card_image_url(self, step):
         return program.card_image_url
 
     def get_courses(self, obj):
-        excluded_restriction_types = get_excluded_restriction_types(self.context['request'])
-        return obj.get_linked_courses_and_course_runs(excluded_restriction_types=excluded_restriction_types)
+        return obj.get_linked_courses_and_course_runs()
 
 
 class LearnerPathwayBlockSerializer(serializers.ModelSerializer):