Respect querystring parameters when caching retrieve responses

The DefaultObjectKeyConstructor doesn't include querystring parameters in its cache key.

LEARNER-401

course_discovery/apps/api/cache.py

@@ -2,7 +2,7 @@ import logging
 import time
 
 from django.core.cache import cache
-from rest_framework_extensions.key_constructor.bits import KeyBitBase
+from rest_framework_extensions.key_constructor.bits import KeyBitBase, QueryParamsKeyBit
 from rest_framework_extensions.key_constructor.constructors import (
     DefaultListKeyConstructor, DefaultObjectKeyConstructor
 )
@@ -22,6 +22,9 @@ class TimestampedListKeyConstructor(DefaultListKeyConstructor):
 
 class TimestampedObjectKeyConstructor(DefaultObjectKeyConstructor):
     timestamp = ApiTimestampKeyBit()
+    # The DefaultObjectKeyConstructor doesn't include querystring parameters
+    # in its cache key.
+    querystring = QueryParamsKeyBit()
 
 
 def timestamped_list_key_constructor(*args, **kwargs):  # pylint: disable=unused-argument

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

+import urllib.parse
+
 import ddt
 from django.core.cache import cache
 from django.core.urlresolvers import reverse
@@ -48,10 +50,13 @@ class ProgramViewSetTests(SerializationMixin, APITestCase):
         )
         return program
 
-    def assert_retrieve_success(self, program):
+    def assert_retrieve_success(self, program, querystring=None):
         """ Verify the retrieve endpoint succesfully returns a serialized program. """
         url = reverse('api:v1:program-detail', kwargs={'uuid': program.uuid})
 
+        if querystring:
+            url += '?' + urllib.parse.urlencode(querystring)
+
         response = self.client.get(url)
         self.assertEqual(response.status_code, 200)
         return response
@@ -77,6 +82,10 @@ class ProgramViewSetTests(SerializationMixin, APITestCase):
         with self.assertNumQueries(2):
             self.assert_retrieve_success(program)
 
+        # Verify that requests including querystring parameters are cached separately.
+        response = self.assert_retrieve_success(program, querystring={'use_full_course_serializer': 1})
+        assert response.data == self.serialize_program(program, extra_context={'use_full_course_serializer': 1})
+
     @ddt.data(True, False)
     def test_retrieve_with_sorting_flag(self, order_courses_by_start_date):
         """ Verify the number of queries is the same with sorting flag set to true. """