Merge pull request #1738 from MITx/fix/cdodge/too-many-depth-levels

it appears we are taking one too many round trips to do when pre-fetchin...

cms/djangoapps/contentstore/tests/test_contentstore.py

@@ -37,6 +37,14 @@ TEST_DATA_MODULESTORE = copy.deepcopy(settings.MODULESTORE)
 TEST_DATA_MODULESTORE['default']['OPTIONS']['fs_root'] = path('common/test/data')
 TEST_DATA_MODULESTORE['direct']['OPTIONS']['fs_root'] = path('common/test/data')
 
+class MongoCollectionFindWrapper(object):
+    def __init__(self, original):
+        self.original = original
+        self.counter = 0
+
+    def find(self, query, *args, **kwargs):
+        self.counter = self.counter+1
+        return self.original(query, *args, **kwargs)
 
 @override_settings(MODULESTORE=TEST_DATA_MODULESTORE)
 class ContentStoreToyCourseTest(ModuleStoreTestCase):
@@ -145,8 +153,6 @@ class ContentStoreToyCourseTest(ModuleStoreTestCase):
         # make sure the parent no longer points to the child object which was deleted
         self.assertFalse(sequential.location.url() in chapter.children)
 
-
-
     def test_about_overrides(self):
         '''
         This test case verifies that a course can use specialized override for about data, e.g. /about/Fall_2012/effort.html
@@ -307,6 +313,28 @@ class ContentStoreToyCourseTest(ModuleStoreTestCase):
         # note, we know the link it should be because that's what in the 'full' course in the test data
         self.assertContains(resp, '/c4x/edX/full/asset/handouts_schematic_tutorial.pdf')
 
+    def test_prefetch_children(self):
+        import_from_xml(modulestore(), 'common/test/data/', ['full'])
+        module_store = modulestore('direct')
+        location = CourseDescriptor.id_to_location('edX/full/6.002_Spring_2012')
+
+        wrapper = MongoCollectionFindWrapper(module_store.collection.find)
+        module_store.collection.find = wrapper.find
+        course = module_store.get_item(location, depth=2)
+
+        # make sure we haven't done too many round trips to DB
+        # note we say 4 round trips here for 1) the course, 2 & 3) for the chapters and sequentials, and
+        # 4) because of the RT due to calculating the inherited metadata
+        self.assertEqual(wrapper.counter, 4)
+
+        # make sure we pre-fetched a known sequential which should be at depth=2
+        self.assertTrue(Location(['i4x', 'edX', 'full', 'sequential', 
+            'Administrivia_and_Circuit_Elements', None]) in course.system.module_data)
+
+        # make sure we don't have a specific vertical which should be at depth=3
+        self.assertFalse(Location(['i4x', 'edX', 'full', 'vertical', 'vertical_58', 
+            None]) in course.system.module_data)
+
     def test_export_course_with_unknown_metadata(self):
         module_store = modulestore('direct')
         content_store = contentstore()

common/lib/xmodule/xmodule/modulestore/mongo.py

@@ -366,6 +366,9 @@ class MongoModuleStore(ModuleStoreBase):
                 children.extend(item.get('definition', {}).get('children', []))
                 data[Location(item['location'])] = item
 
+            if depth == 0:
+                break;
+
             # Load all children by id. See
             # http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24or
             # for or-query syntax