Add option to serialize only program UUIDs

ProgramViewSet.list now returns a flat list of program UUIDs when `uuids_only=1` is included in the querystring. This allows clients which cache each program in an individual entry (e.g., LMS) to more quickly identify the programs they need to get from their cache.

LEARNER-382

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

@@ -137,6 +137,28 @@ class ProgramViewSetTests(SerializationMixin, APITestCase):
         # Verify that repeated list requests use the cache.
         self.assert_list_results(self.list_path, expected, 2)
 
+    def test_uuids_only(self):
+        """
+        Verify that the list view returns a simply list of UUIDs when the
+        uuids_only query parameter is passed.
+        """
+        active = ProgramFactory.create_batch(3)
+        retired = [ProgramFactory(status=ProgramStatus.Retired)]
+        programs = active + retired
+
+        querystring = {'uuids_only': 1}
+        url = '{base}?{query}'.format(base=self.list_path, query=urllib.parse.urlencode(querystring))
+        response = self.client.get(url)
+
+        assert set(response.data) == {program.uuid for program in programs}
+
+        # Verify that filtering (e.g., by status) is still supported.
+        querystring['status'] = ProgramStatus.Retired
+        url = '{base}?{query}'.format(base=self.list_path, query=urllib.parse.urlencode(querystring))
+        response = self.client.get(url)
+
+        assert set(response.data) == {program.uuid for program in retired}
+
     def test_filter_by_type(self):
         """ Verify that the endpoint filters programs to those of a given type. """
         program_type_name = 'foo'

course_discovery/apps/api/v1/views/programs.py

 from rest_framework import mixins, viewsets
 from rest_framework.filters import DjangoFilterBackend
 from rest_framework.permissions import IsAuthenticated
+from rest_framework.response import Response
 from rest_framework_extensions.cache.mixins import CacheResponseMixin
 
 from course_discovery.apps.api import filters, serializers
 from course_discovery.apps.api.pagination import ProxiedPagination
 from course_discovery.apps.api.v1.views import get_query_param
-from course_discovery.apps.course_metadata.models import ProgramType
+from course_discovery.apps.course_metadata.models import Program, ProgramType
 
 
 # pylint: disable=no-member
@@ -91,6 +92,14 @@ class ProgramViewSet(CacheResponseMixin, viewsets.ReadOnlyModelViewSet):
               paramType: query
               multiple: false
         """
+        if get_query_param(self.request, 'uuids_only'):
+            # DRF serializers don't have good support for simple, flat
+            # representations like the one we want here.
+            queryset = self.filter_queryset(Program.objects.all())
+            uuids = queryset.values_list('uuid', flat=True)
+
+            return Response(uuids)
+
         return super(ProgramViewSet, self).list(request, *args, **kwargs)