Cache CcxFieldOverrides on a per-request basis

lms/djangoapps/ccx/overrides.py

@@ -84,35 +84,40 @@ def get_override_for_ccx(ccx, block, name, default=None):
     specify the block and the name of the field.  If the field is not
     overridden for the given ccx, returns `default`.
     """
-    if not hasattr(block, '_ccx_overrides'):
-        block._ccx_overrides = {}  # pylint: disable=protected-access
-    overrides = block._ccx_overrides.get(ccx.id)  # pylint: disable=protected-access
-    if overrides is None:
-        overrides = _get_overrides_for_ccx(ccx, block)
-        block._ccx_overrides[ccx.id] = overrides  # pylint: disable=protected-access
-    return overrides.get(name, default)
+    overrides = _get_overrides_for_ccx(ccx)
+
+    if isinstance(block.location, CCXBlockUsageLocator):
+        non_ccx_key = block.location.to_block_locator()
+    else:
+        non_ccx_key = block.location
+
+    block_overrides = overrides.get(non_ccx_key, {})
+    if name in block_overrides:
+        return block.fields[name].from_json(block_overrides[name])
+    else:
+        return default
 
 
-def _get_overrides_for_ccx(ccx, block):
+def _get_overrides_for_ccx(ccx):
     """
     Returns a dictionary mapping field name to overriden value for any
     overrides set on this block for this CCX.
     """
-    overrides = {}
-    # block as passed in may have a location specific to a CCX, we must strip
-    # that for this query
-    location = block.location
-    if isinstance(block.location, CCXBlockUsageLocator):
-        location = block.location.to_block_locator()
-    query = CcxFieldOverride.objects.filter(
-        ccx=ccx,
-        location=location
-    )
-    for override in query:
-        field = block.fields[override.field]
-        value = field.from_json(json.loads(override.value))
-        overrides[override.field] = value
-    return overrides
+    overrides_cache = request_cache.get_cache('ccx-overrides')
+
+    if ccx not in overrides_cache:
+        overrides = {}
+        query = CcxFieldOverride.objects.filter(
+            ccx=ccx,
+        )
+
+        for override in query:
+            block_overrides = overrides.setdefault(override.location, {})
+            block_overrides[override.field] = json.loads(override.value)
+
+        overrides_cache[ccx] = overrides
+
+    return overrides_cache[ccx]
 
 
 @transaction.commit_on_success
@@ -123,23 +128,25 @@ def override_field_for_ccx(ccx, block, name, value):
     value to set for the given field.
     """
     field = block.fields[name]
-    value = json.dumps(field.to_json(value))
+    value_json = field.to_json(value)
+    serialized_value = json.dumps(value_json)
     try:
         override = CcxFieldOverride.objects.create(
             ccx=ccx,
             location=block.location,
             field=name,
-            value=value)
+            value=serialized_value
+        )
     except IntegrityError:
         transaction.commit()
         override = CcxFieldOverride.objects.get(
             ccx=ccx,
             location=block.location,
-            field=name)
-        override.value = value
+            field=name
+        )
+        override.value = serialized_value
     override.save()
-    if hasattr(block, '_ccx_overrides'):
-        del block._ccx_overrides[ccx.id]  # pylint: disable=protected-access
+    _get_overrides_for_ccx(ccx).setdefault(block.location, {})[name] = value_json
 
 
 def clear_override_for_ccx(ccx, block, name):
@@ -155,8 +162,7 @@ def clear_override_for_ccx(ccx, block, name):
             location=block.location,
             field=name).delete()
 
-        if hasattr(block, '_ccx_overrides'):
-            del block._ccx_overrides[ccx.id]  # pylint: disable=protected-access
+        _get_overrides_for_ccx(ccx).setdefault(block.location, {}).pop(name)
 
     except CcxFieldOverride.DoesNotExist:
         pass

lms/djangoapps/ccx/tests/test_field_override_performance.py

@@ -250,9 +250,9 @@ class TestFieldOverrideSplitPerformance(FieldOverridePerformanceTestCase):
         ('ccx', 1, True, False): (23, 4, 9),
         ('ccx', 2, True, False): (68, 19, 54),
         ('ccx', 3, True, False): (263, 84, 215),
-        ('ccx', 1, True, True): (33, 4, 13),
-        ('ccx', 2, True, True): (68, 19, 84),
-        ('ccx', 3, True, True): (263, 84, 335),
+        ('ccx', 1, True, True): (25, 4, 13),
+        ('ccx', 2, True, True): (70, 19, 84),
+        ('ccx', 3, True, True): (265, 84, 335),
         ('no_overrides', 1, False, False): (23, 4, 9),
         ('no_overrides', 2, False, False): (68, 19, 54),
         ('no_overrides', 3, False, False): (263, 84, 215),

lms/djangoapps/ccx/tests/test_overrides.py

@@ -100,7 +100,7 @@ class TestFieldOverrides(ModuleStoreTestCase):
         """
         ccx_start = datetime.datetime(2014, 12, 25, 00, 00, tzinfo=pytz.UTC)
         chapter = self.ccx.course.get_children()[0]
-        with self.assertNumQueries(4):
+        with self.assertNumQueries(3):
             override_field_for_ccx(self.ccx, chapter, 'start', ccx_start)
             dummy = chapter.start
 
@@ -110,7 +110,7 @@ class TestFieldOverrides(ModuleStoreTestCase):
         """
         ccx_start = datetime.datetime(2014, 12, 25, 00, 00, tzinfo=pytz.UTC)
         chapter = self.ccx.course.get_children()[0]
-        with self.assertNumQueries(4):
+        with self.assertNumQueries(3):
             override_field_for_ccx(self.ccx, chapter, 'start', ccx_start)
             dummy1 = chapter.start
             dummy2 = chapter.start

lms/djangoapps/ccx/tests/test_views.py

@@ -21,6 +21,7 @@ from django.test.utils import override_settings
 from django.test import RequestFactory
 from edxmako.shortcuts import render_to_response  # pylint: disable=import-error
 from student.models import CourseEnrollment
+from request_cache.middleware import RequestCache
 from student.roles import CourseCcxCoachRole  # pylint: disable=import-error
 from student.tests.factories import (  # pylint: disable=import-error
     AdminFactory,
@@ -503,26 +504,6 @@ class TestCCXGrades(ModuleStoreTestCase, LoginEnrollmentTestCase):
         role.add_users(coach)
         ccx = CcxFactory(course_id=course.id, coach=self.coach)
 
-        # Apparently the test harness doesn't use LmsFieldStorage, and I'm not
-        # sure if there's a way to poke the test harness to do so.  So, we'll
-        # just inject the override field storage in this brute force manner.
-        OverrideFieldData.provider_classes = None
-        # pylint: disable=protected-access
-        for block in iter_blocks(course):
-            block._field_data = OverrideFieldData.wrap(coach, course, block._field_data)
-            new_cache = {'tabs': [], 'discussion_topics': []}
-            if 'grading_policy' in block._field_data_cache:
-                new_cache['grading_policy'] = block._field_data_cache['grading_policy']
-            block._field_data_cache = new_cache
-
-        def cleanup_provider_classes():
-            """
-            After everything is done, clean up by un-doing the change to the
-            OverrideFieldData object that is done during the wrap method.
-            """
-            OverrideFieldData.provider_classes = None
-        self.addCleanup(cleanup_provider_classes)
-
         # override course grading policy and make last section invisible to students
         override_field_for_ccx(ccx, course, 'grading_policy', {
             'GRADER': [
@@ -561,9 +542,13 @@ class TestCCXGrades(ModuleStoreTestCase, LoginEnrollmentTestCase):
 
         self.client.login(username=coach.username, password="test")
 
+        self.addCleanup(RequestCache.clear_request_cache)
+
     @patch('ccx.views.render_to_response', intercept_renderer)
     def test_gradebook(self):
         self.course.enable_ccx = True
+        RequestCache.clear_request_cache()
+
         url = reverse(
             'ccx_gradebook',
             kwargs={'course_id': self.ccx_key}
@@ -580,6 +565,8 @@ class TestCCXGrades(ModuleStoreTestCase, LoginEnrollmentTestCase):
 
     def test_grades_csv(self):
         self.course.enable_ccx = True
+        RequestCache.clear_request_cache()
+
         url = reverse(
             'ccx_grades_csv',
             kwargs={'course_id': self.ccx_key}
@@ -591,11 +578,11 @@ class TestCCXGrades(ModuleStoreTestCase, LoginEnrollmentTestCase):
             response.content.strip().split('\n')
         )
         data = dict(zip(headers, row))
+        self.assertTrue('HW 04' not in data)
         self.assertEqual(data['HW 01'], '0.75')
         self.assertEqual(data['HW 02'], '0.5')
         self.assertEqual(data['HW 03'], '0.25')
         self.assertEqual(data['HW Avg'], '0.5')
-        self.assertTrue('HW 04' not in data)
 
     @patch('courseware.views.render_to_response', intercept_renderer)
     def test_student_progress(self):