Cache anonymous user id on the user object, so that queries aren't made many…

Cache anonymous user id on the user object, so that queries aren't made many times over during module rendering

common/djangoapps/student/models.py

@@ -66,6 +66,10 @@ def anonymous_id_for_user(user, course_id):
     if user.is_anonymous():
         return None
 
+    cached_id = getattr(user, '_anonymous_id', {}).get(course_id)
+    if cached_id is not None:
+        return cached_id
+
     # include the secret key as a salt, and to make the ids unique across different LMS installs.
     hasher = hashlib.md5()
     hasher.update(settings.SECRET_KEY)
@@ -94,6 +98,11 @@ def anonymous_id_for_user(user, course_id):
         # continue
         pass
 
+    if not hasattr(user, '_anonymous_id'):
+        user._anonymous_id = {}
+
+    user._anonymous_id[course_id] = digest
+
     return digest