Respect all querystring parameters when caching list responses

The DefaultListKeyConstructor includes the PaginationKeyBit. While it does subclass QueryParamsKeyBit, it also bypasses logic which includes all query params in the cache key, restricting the set of query params that end up in the cache key to those that are used for page number pagination. This causes cache collisions when other query params are involved.

LEARNER-1072

course_discovery/apps/api/cache.py

@@ -18,6 +18,13 @@ class ApiTimestampKeyBit(KeyBitBase):
 
 class TimestampedListKeyConstructor(DefaultListKeyConstructor):
     timestamp = ApiTimestampKeyBit()
+    # The DefaultListKeyConstructor includes the PaginationKeyBit. While it does
+    # subclass QueryParamsKeyBit, it also bypasses logic which includes all query
+    # params in the cache key, restricting the set of query params that end up in
+    # the cache key to those that are used for page number pagination. This causes
+    # cache collisions when other query params are involved. For more, see:
+    # https://github.com/chibisov/drf-extensions/blob/master/rest_framework_extensions/key_constructor/bits.py#L48-L49
+    querystring = QueryParamsKeyBit()
 
 
 class TimestampedObjectKeyConstructor(DefaultObjectKeyConstructor):