exclude topics with no associated channel in api responses

learning_resources/views.py

@@ -591,6 +591,10 @@ class TopicViewSet(viewsets.ReadOnlyModelViewSet):
     filter_backends = [DjangoFilterBackend]
     filterset_class = TopicFilter
 
+    def filter_queryset(self, queryset):
+        queryset = queryset.exclude(channel_url__isnull=True)
+        return super().filter_queryset(queryset)
+
     @method_decorator(
         cache_page_for_all_users(
             settings.SEARCH_PAGE_CACHE_DURATION, cache="redis", key_prefix="search"

learning_resources/views_test.py

@@ -547,6 +547,8 @@ def test_topics_list_endpoint(client, django_assert_num_queries):
         LearningResourceTopicFactory.create_batch(100),
         key=lambda topic: topic.name,
     )
+    for topic in topics:
+        ChannelTopicDetailFactory.create(topic=topic)
 
     with django_assert_num_queries(2):
         resp = client.get(reverse("lr:v1:topics_api-list"))
@@ -564,28 +566,27 @@ def test_topics_list_endpoint(client, django_assert_num_queries):
 def test_topics_detail_endpoint(client):
     """Test topics detail endpoint"""
     topic = LearningResourceTopicFactory.create()
+    ChannelTopicDetailFactory.create(topic=topic)
     resp = client.get(reverse("lr:v1:topics_api-detail", args=[topic.pk]))
     assert resp.data == LearningResourceTopicSerializer(instance=topic).data
 
 
 @pytest.mark.parametrize("published", [True, False])
 def test_topic_channel_url(client, published):
     """
-    Check that the topic API returns 'None' for channel_url of unpublished channels.
-
-    Note: The channel_url being None is also tested on the Channel model itself,
-    but the API may generate the channel_url in a slightly different manner (for
-    example, queryset annotation)
+    Test that topics with published channels return the channel_url,
+    and unpublished channels are not included in the response
     """
     topic = LearningResourceTopicFactory.create()
     channel = ChannelTopicDetailFactory.create(
         topic=topic, is_unpublished=not published
     ).channel
     resp = client.get(reverse("lr:v1:topics_api-detail", args=[topic.pk]))
 
-    assert resp.data["channel_url"] == channel.channel_url
-    if not published:
-        assert resp.data["channel_url"] is None
+    if published:
+        assert resp.data["channel_url"] == channel.channel_url
+    else:
+        assert resp.status_code == 404
 
 
 def test_departments_list_endpoint(client):