Merge pull request #168 from edx/ormsbee/cache_sub

Simple caching of get_submission() requests.

apps/submissions/api.py

@@ -5,6 +5,7 @@ Public interface for the submissions app.
 import copy
 import logging
 
+from django.core.cache import cache
 from django.db import DatabaseError
 from django.utils.encoding import force_unicode
 
@@ -180,9 +181,15 @@ def get_submission(submission_uuid):
             "submission_uuid ({!r}) must be a string type".format(submission_uuid)
         )
 
+    cache_key = "submissions.submission.{}".format(submission_uuid)
+    cached_submission_data = cache.get(cache_key)
+    if cached_submission_data:
+        return cached_submission_data
+
     try:
         submission = Submission.objects.get(uuid=submission_uuid)
-        return SubmissionSerializer(submission).data
+        submission_data = SubmissionSerializer(submission).data
+        cache.set(cache_key, submission_data)
     except Submission.DoesNotExist:
         raise SubmissionNotFoundError(
             u"No submission matching uuid {}".format(submission_uuid)
@@ -193,6 +200,8 @@ def get_submission(submission_uuid):
         logger.exception(err_msg)
         raise SubmissionInternalError(err_msg)
 
+    return submission_data
+
 
 def get_submission_and_student(uuid):
     """

apps/submissions/tests/test_api.py

@@ -76,7 +76,7 @@ class TestSubmissionsApi(TestCase):
 
         # Test not found
         with self.assertRaises(api.SubmissionNotFoundError):
-            api.get_submission("not a real uuid")
+            api.get_submission("notarealuuid")
         with self.assertRaises(api.SubmissionNotFoundError):
             api.get_submission("0" * 50)  # This is bigger than our field size
 
@@ -187,6 +187,21 @@ class TestSubmissionsApi(TestCase):
             item_id=student_item["item_id"]
         )
 
+    def test_caching(self):
+        sub = api.create_submission(STUDENT_ITEM, "Hello World!")
+
+        # The first request to get the submission hits the database...
+        with self.assertNumQueries(1):
+            db_sub = api.get_submission(sub["uuid"])
+
+        # The next one hits the cache only...
+        with self.assertNumQueries(0):
+            cached_sub = api.get_submission(sub["uuid"])
+
+        # The data that gets passed back matches the original in both cases
+        self.assertEqual(sub, db_sub)
+        self.assertEqual(sub, cached_sub)
+
     """
     Testing Scores
     """

settings/base.py

@@ -171,3 +171,10 @@ LOGGING = {
 WORKBENCH = {
     'reset_state_on_restart': False,
 }
+
+CACHES = {
+    'default': {
+        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+        'LOCATION': 'default_loc_mem',
+    },
+}

settings/test.py

@@ -29,3 +29,4 @@ LETTUCE_SERVER_PORT = 8005
 
 # Install test-specific Django apps
 INSTALLED_APPS += ('django_nose', 'lettuce.django',)
+