add some comments regarding which code can be removed when the 'split mongo…

add some comments regarding which code can be removed when the 'split mongo module store' work is completed

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

@@ -29,6 +29,8 @@ class CachingDescriptorSystem(MakoDescriptorSystem):
     """
     A system that has a cache of module json that it will use to load modules
     from, with a backup of calling to the underlying modulestore for more data
+    TODO (cdodge) when the 'split module store' work has been completed we can remove all
+    references to metadata_inheritance_tree
     """
     def __init__(self, modulestore, module_data, default_class, resources_fs,
                  error_tracker, render_template, metadata_inheritance_tree = None):
@@ -153,6 +155,9 @@ class MongoModuleStore(ModuleStoreBase):
         self.metadata_inheritance_cache = {}
 
     def get_metadata_inheritance_tree(self, location):
+        '''
+        TODO (cdodge) This method can be deleted when the 'split module store' work has been completed
+        '''
         
         # get all collections in the course, this query should not return any leaf nodes
         query = { '_id.org' : location.org,
@@ -207,6 +212,9 @@ class MongoModuleStore(ModuleStoreBase):
         return cache
 
     def get_cached_metadata_inheritance_tree(self, location, max_age_allowed):
+        '''
+        TODO (cdodge) This method can be deleted when the 'split module store' work has been completed
+        '''
         cache_name = '{0}/{1}'.format(location.org, location.course)
         cache = self.metadata_inheritance_cache.get(cache_name,{'parent_metadata': {}, 
             'timestamp': datetime.now() - timedelta(hours=1)})
@@ -274,6 +282,8 @@ class MongoModuleStore(ModuleStoreBase):
 
         resource_fs = OSFS(root)
 
+        # TODO (cdodge): When the 'split module store' work has been completed, we should remove
+        # the 'metadata_inheritance_tree' parameter
         system = CachingDescriptorSystem(
             self,
             data_cache,