Add endpoint to get user list for a preference

The endpoint includes the key of the desired preference in the URL and
returns the list of users for whom the preference is set (regardless of
the value).

common/djangoapps/user_api/models.py

 from django.contrib.auth.models import User
+from django.core.validators import RegexValidator
 from django.db import models
 
 
 class UserPreference(models.Model):
     """A user's preference, stored as generic text to be processed by client"""
+    KEY_REGEX = r"[-_a-zA-Z0-9]+"
     user = models.ForeignKey(User, db_index=True, related_name="preferences")
-    key = models.CharField(max_length=255, db_index=True)
+    key = models.CharField(max_length=255, db_index=True, validators=[RegexValidator(KEY_REGEX)])
     value = models.TextField()
 
     class Meta:

common/djangoapps/user_api/tests/test_views.py

@@ -373,3 +373,59 @@ class UserPreferenceViewSetTest(UserApiTestCase):
                 "url": uri,
             }
         )
+
+
+class PreferenceUsersListViewTest(UserApiTestCase):
+    LIST_URI = "/user_api/v1/preferences/key0/users/"
+
+    def test_options(self):
+        self.assertAllowedMethods(self.LIST_URI, ["OPTIONS", "GET", "HEAD"])
+
+    def test_put_not_allowed(self):
+        self.assertHttpMethodNotAllowed(self.request_with_auth("put", self.LIST_URI))
+
+    def test_patch_not_allowed(self):
+        raise SkipTest("Django 1.4's test client does not support patch")
+
+    def test_delete_not_allowed(self):
+        self.assertHttpMethodNotAllowed(self.request_with_auth("delete", self.LIST_URI))
+
+    def test_unauthorized(self):
+        self.assertHttpForbidden(self.client.get(self.LIST_URI))
+
+    @override_settings(DEBUG=True)
+    @override_settings(EDX_API_KEY=None)
+    def test_debug_auth(self):
+        self.assertHttpOK(self.client.get(self.LIST_URI))
+
+    def test_get_basic(self):
+        result = self.get_json(self.LIST_URI)
+        self.assertEqual(result["count"], 2)
+        self.assertIsNone(result["next"])
+        self.assertIsNone(result["previous"])
+        users = result["results"]
+        self.assertEqual(len(users), 2)
+        for user in users:
+            self.assertUserIsValid(user)
+
+    def test_get_pagination(self):
+        first_page = self.get_json(self.LIST_URI, data={"page_size": 1})
+        self.assertEqual(first_page["count"], 2)
+        first_page_next_uri = first_page["next"]
+        self.assertIsNone(first_page["previous"])
+        first_page_users = first_page["results"]
+        self.assertEqual(len(first_page_users), 1)
+
+        second_page = self.get_json(first_page_next_uri)
+        self.assertEqual(second_page["count"], 2)
+        self.assertIsNone(second_page["next"])
+        second_page_prev_uri = second_page["previous"]
+        second_page_users = second_page["results"]
+        self.assertEqual(len(second_page_users), 1)
+
+        self.assertEqual(self.get_json(second_page_prev_uri), first_page)
+
+        for user in first_page_users + second_page_users:
+            self.assertUserIsValid(user)
+        all_user_uris = [user["url"] for user in first_page_users + second_page_users]
+        self.assertEqual(len(set(all_user_uris)), 2)

common/djangoapps/user_api/urls.py

 from django.conf.urls import include, patterns, url
 from rest_framework import routers
 from user_api import views as user_api_views
+from user_api.models import UserPreference
 
 
 user_api_router = routers.DefaultRouter()
@@ -9,4 +10,8 @@ user_api_router.register(r'user_prefs', user_api_views.UserPreferenceViewSet)
 urlpatterns = patterns(
     '',
     url(r'^v1/', include(user_api_router.urls)),
+    url(
+        r'^v1/preferences/(?P<pref_key>{})/users/$'.format(UserPreference.KEY_REGEX),
+        user_api_views.PreferenceUsersListView.as_view()
+    ),
 )

common/djangoapps/user_api/views.py

@@ -2,6 +2,7 @@ from django.conf import settings
 from django.contrib.auth.models import User
 from rest_framework import authentication
 from rest_framework import filters
+from rest_framework import generics
 from rest_framework import permissions
 from rest_framework import viewsets
 from user_api.serializers import UserSerializer, UserPreferenceSerializer
@@ -43,3 +44,14 @@ class UserPreferenceViewSet(viewsets.ReadOnlyModelViewSet):
     serializer_class = UserPreferenceSerializer
     paginate_by = 10
     paginate_by_param = "page_size"
+
+
+class PreferenceUsersListView(generics.ListAPIView):
+    authentication_classes = (authentication.SessionAuthentication,)
+    permission_classes = (ApiKeyHeaderPermission,)
+    serializer_class = UserSerializer
+    paginate_by = 10
+    paginate_by_param = "page_size"
+
+    def get_queryset(self):
+        return User.objects.filter(preferences__key=self.kwargs["pref_key"]).prefetch_related("preferences")