Version assessment model cache keys

apps/openassessment/assessment/serializers.py

@@ -7,7 +7,6 @@ from copy import deepcopy
 import logging
 
 from django.core.cache import cache
-from django.utils.translation import ugettext as _
 from rest_framework import serializers
 from openassessment.assessment.models import (
     Assessment, AssessmentPart, Criterion, CriterionOption, Rubric,
@@ -19,6 +18,26 @@ from openassessment.assessment.models import (
 logger = logging.getLogger(__name__)
 
 
+# Current version of the models in the cache
+# Increment this to ignore assessment models currently in the cache
+# when model fields change.
+CACHE_VERSION = 1
+
+
+def _versioned_cache_key(key):
+    """
+    Add a version number to a cache key, so we
+
+    Args:
+        key (unicode): The original, unversioned, cache key.
+
+    Returns:
+        unicode: Cache key with the version appended.
+
+    """
+    return u"{}.v{}".format(key, CACHE_VERSION)
+
+
 class InvalidRubric(Exception):
     """This can be raised during the deserialization process."""
     def __init__(self, errors):
@@ -202,8 +221,10 @@ def full_assessment_dict(assessment, rubric_dict=None):
     Returns:
         dict with keys 'rubric' (serialized Rubric model) and 'parts' (serialized assessment parts)
     """
-    assessment_cache_key = "assessment.full_assessment_dict.{}.{}.{}".format(
-        assessment.id, assessment.submission_uuid, assessment.scored_at.isoformat()
+    assessment_cache_key = _versioned_cache_key(
+        "assessment.full_assessment_dict.{}.{}.{}".format(
+            assessment.id, assessment.submission_uuid, assessment.scored_at.isoformat()
+        )
     )
     assessment_dict = cache.get(assessment_cache_key)
     if assessment_dict: