feat: add API to return list of downstream contexts for an upstream

cms/djangoapps/contentstore/models.py

@@ -202,6 +202,15 @@ def get_by_downstream_context(cls, downstream_context_key: CourseKey) -> QuerySe
             "upstream_block__learning_package"
         )
 
+    @classmethod
+    def get_by_upstream_usage_key(cls, upstream_usage_key: UsageKey) -> QuerySet["PublishableEntityLink"]:
+        """
+        Get all downstream context keys for given upstream usage key
+        """
+        return cls.objects.filter(
+            upstream_usage_key=upstream_usage_key,
+        )
+
 
 class LearningContextLinksStatusChoices(models.TextChoices):
     """

cms/djangoapps/contentstore/rest_api/v2/urls.py

@@ -29,6 +29,11 @@
         downstreams.UpstreamListView.as_view(),
         name='upstream-list'
     ),
+    re_path(
+        f'^upstream/{settings.USAGE_KEY_PATTERN}/downstream-contexts$',
+        downstreams.DownstreamContextListView.as_view(),
+        name='downstream-context-list'
+    ),
     re_path(
         fr'^downstreams/{settings.USAGE_KEY_PATTERN}/sync$',
         downstreams.SyncFromUpstreamView.as_view(),

cms/djangoapps/contentstore/rest_api/v2/views/downstreams.py

@@ -40,6 +40,12 @@
       400: Downstream block is not linked to upstream content.
       404: Downstream block not found or user lacks permission to edit it.
 
+  /api/contentstore/v2/upstream/{usage_key_string}/downstream-contexts
+
+    GET: List all downstream contexts (Courses) linked to a library block.
+        200: A list of Course IDs and their display names, along with the number of times the block
+            is linked to each.
+
   # NOT YET IMPLEMENTED -- Will be needed for full Libraries Relaunch in ~Teak.
   /api/contentstore/v2/downstreams
   /api/contentstore/v2/downstreams?course_id=course-v1:A+B+C&ready_to_sync=true
@@ -60,6 +66,7 @@
 import logging
 
 from attrs import asdict as attrs_asdict
+from collections import Counter
 from django.contrib.auth.models import User  # pylint: disable=imported-auth-user
 from opaque_keys import InvalidKeyError
 from opaque_keys.edx.keys import CourseKey, UsageKey
@@ -71,6 +78,7 @@
 
 from cms.djangoapps.contentstore.helpers import import_static_assets_for_library_sync
 from cms.djangoapps.contentstore.models import PublishableEntityLink
+from cms.djangoapps.contentstore.utils import reverse_course_url
 from cms.djangoapps.contentstore.rest_api.v2.serializers import PublishableEntityLinksSerializer
 from cms.lib.xblock.upstream_sync import (
     BadDownstream,
@@ -91,6 +99,7 @@
 from xmodule.modulestore.django import modulestore
 from xmodule.modulestore.exceptions import ItemNotFoundError
 
+
 logger = logging.getLogger(__name__)
 
 
@@ -124,7 +133,7 @@ class UpstreamListView(DeveloperErrorViewMixin, APIView):
     """
     Serves course->library publishable entity links
     """
-    def get(self, request: _AuthenticatedRequest, course_key_string: str):
+    def get(self, _: _AuthenticatedRequest, course_key_string: str):
         """
         Fetches publishable entity links for given course key
         """
@@ -137,6 +146,40 @@ def get(self, request: _AuthenticatedRequest, course_key_string: str):
         return Response(serializer.data)
 
 
+@view_auth_classes()
+class DownstreamContextListView(DeveloperErrorViewMixin, APIView):
+    """
+    Serves library block->courses links
+    """
+    def get(self, _: _AuthenticatedRequest, usage_key_string: str) -> Response:
+        """
+        Fetches downstream context links for given publishable entity
+        """
+        try:
+            usage_key = UsageKey.from_string(usage_key_string)
+            print(usage_key)
+        except InvalidKeyError as exc:
+            raise ValidationError(detail=f"Malformed usage key: {usage_key_string}") from exc
+        links = PublishableEntityLink.get_by_upstream_usage_key(upstream_usage_key=usage_key)
+        downstream_key_list = [link.downstream_context_key for link in links]
+
+        # Count the number of times each course is linked to the library block
+        counter = Counter(downstream_key_list)
+
+        result = []
+        for context_key, count in counter.most_common():
+            # The following code only can handle the correct display_name for Courses as context
+            course = modulestore().get_course(context_key)
+            result.append({
+                "id": str(context_key),
+                "display_name": course.display_name,
+                "url": reverse_course_url('course_handler', context_key),
+                "count": count,
+            })
+
+        return Response(result)
+
+
 @view_auth_classes(is_authenticated=True)
 class DownstreamView(DeveloperErrorViewMixin, APIView):
     """

cms/djangoapps/contentstore/rest_api/v2/views/tests/test_downstreams.py

@@ -66,6 +66,17 @@ def setUp(self):
         self.downstream_html_key = BlockFactory.create(
             category='html', parent=unit, upstream=MOCK_HTML_UPSTREAM_REF, upstream_version=1,
         ).usage_key
+
+        self.another_course = CourseFactory.create(display_name="Another Course")
+        another_chapter = BlockFactory.create(category='chapter', parent=self.another_course)
+        another_sequential = BlockFactory.create(category='sequential', parent=another_chapter)
+        another_unit = BlockFactory.create(category='vertical', parent=another_sequential)
+        for _ in range(3):
+            # Adds 3 videos linked to the same upstream
+            BlockFactory.create(
+                category='video', parent=another_unit, upstream=MOCK_UPSTREAM_REF, upstream_version=123,
+            )
+
         self.fake_video_key = self.course.id.make_usage_key("video", "NoSuchVideo")
         self.superuser = UserFactory(username="superuser", password="password", is_staff=True, is_superuser=True)
         self.learner = UserFactory(username="learner", password="password")
@@ -339,3 +350,36 @@ def test_200_all_upstreams(self):
             },
         ]
         self.assertListEqual(data, expected)
+
+
+class GetDownstreamContextsTest(_BaseDownstreamViewTestMixin, SharedModuleStoreTestCase):
+    """
+    Test that `GET /api/v2/contentstore/upstream/:usage_key/downstream-contexts returns list of
+    link contexts (i.e. courses) in given upstream entity (i.e. library block).
+    """
+    def call_api(self, usage_key_string):
+        return self.client.get(f"/api/contentstore/v2/upstream/{usage_key_string}/downstream-contexts")
+
+    def test_200_downstream_context_list(self):
+        """
+        Returns all downstream courses for given library block
+        """
+        self.client.login(username="superuser", password="password")
+        response = self.call_api(MOCK_UPSTREAM_REF)
+        assert response.status_code == 200
+        data = response.json()
+        expected = [
+            {
+                'id': str(self.another_course.id),
+                'display_name': str(self.another_course.display_name),
+                'url': f'/course/{str(self.another_course.id)}',
+                'count': 3,
+            },
+            {
+                'id': str(self.course.id),
+                'display_name': str(self.course.display_name),
+                'url': f'/course/{str(self.course.id)}',
+                'count': 1,
+            },
+        ]
+        self.assertListEqual(data, expected)