WIP. Trying to fix inheritance

common/lib/xmodule/xmodule/modulestore/xml.py

@@ -422,7 +422,32 @@ class XMLModuleStore(ModuleStoreBase):
             # breaks metadata inheritance via get_children().  Instead
             # (actually, in addition to, for now), we do a final inheritance pass
             # after we have the course descriptor.
-            #XModuleDescriptor.compute_inherited_metadata(course_descriptor)
+            def compute_inherited_metadata(descriptor):
+                """Given a descriptor, traverse all of its descendants and do metadata
+                inheritance.  Should be called on a CourseDescriptor after importing a
+                course.
+
+                NOTE: This means that there is no such thing as lazy loading at the
+                moment--this accesses all the children."""
+                for child in descriptor.get_children():
+                    inherit_metadata(child, descriptor.metadata)
+                    compute_inherited_metadata(child)
+
+            def inherit_metadata(descriptor, metadata):
+                """
+                Updates this module with metadata inherited from a containing module.
+                Only metadata specified in self.inheritable_metadata will
+                be inherited
+                """
+                # Set all inheritable metadata from kwargs that are
+                # in self.inheritable_metadata and aren't already set in metadata
+                for attr in self.inheritable_metadata:
+                    if attr not in self.metadata and attr in metadata:
+                        self._inherited_metadata.add(attr)
+                        self.metadata[attr] = metadata[attr]
+
+
+            compute_inherited_metadata(course_descriptor)
 
             # now import all pieces of course_info which is expected to be stored
             # in <content_dir>/info or <content_dir>/info/<url_name>

common/lib/xmodule/xmodule/runtime.py

@@ -0,0 +1,92 @@
+from collections import MutableMapping, namedtuple
+
+from .model import ModuleScope, ModelType
+
+
+class KeyValueStore(object):
+    """The abstract interface for Key Value Stores."""
+
+    # Keys are structured to retain information about the scope of the data.
+    # Stores can use this information however they like to store and retrieve
+    # data.
+    Key = namedtuple("Key", "scope, student_id, module_scope_id, field_name")
+
+    def get(key):
+        pass
+
+    def set(key, value):
+        pass
+
+    def delete(key):
+        pass
+
+
+class DbModel(MutableMapping):
+    """A dictionary-like interface to the fields on a module."""
+
+    def __init__(self, kvs, module_cls, student_id, usage):
+        self._kvs = kvs
+        self._student_id = student_id
+        self._module_cls = module_cls
+        self._usage = usage
+
+    def __repr__(self):
+        return "<{0.__class__.__name__} {0._module_cls!r}>".format(self)
+
+    def __str__(self):
+        return str(dict(self.iteritems()))
+
+    def _getfield(self, name):
+        if (not hasattr(self._module_cls, name) or
+            not isinstance(getattr(self._module_cls, name), ModelType)):
+
+            raise KeyError(name)
+
+        return getattr(self._module_cls, name)
+
+    def _key(self, name):
+        field = self._getfield(name)
+        module = field.scope.module
+
+        if module == ModuleScope.ALL:
+            module_id = None
+        elif module == ModuleScope.USAGE:
+            module_id = self._usage.id
+        elif module == ModuleScope.DEFINITION:
+            module_id = self._usage.def_id
+        elif module == ModuleScope.TYPE:
+            module_id = self.module_type.__name__
+
+        if field.scope.student:
+            student_id = self._student_id
+        else:
+            student_id = None
+
+        key = KeyValueStore.Key(
+            scope=field.scope,
+            student_id=student_id,
+            module_scope_id=module_id,
+            field_name=name
+            )
+        return key
+
+    def __getitem__(self, name):
+        return self._kvs.get(self._key(name))
+
+    def __setitem__(self, name, value):
+        self._kvs.set(self._key(name), value)
+
+    def __delitem__(self, name):
+        self._kvs.delete(self._key(name))
+
+    def __iter__(self):
+        return iter(self.keys())
+
+    def __len__(self):
+        return len(self.keys())
+
+    def keys(self):
+        fields = [field.name for field in self._module_cls.fields]
+        for namespace_name in self._module_cls.namespaces:
+            fields.extend(field.name for field in getattr(self._module_cls, namespace_name))
+        return fields

common/lib/xmodule/xmodule/x_module.py

@@ -417,15 +417,10 @@ class XModuleDescriptor(Plugin, HTMLSnippet, ResourceTemplates):
                 except ItemNotFoundError:
                     log.exception('Unable to load item {loc}, skipping'.format(loc=child_loc))
                     continue
-                # TODO (vshnayder): this should go away once we have
-                # proper inheritance support in mongo.  The xml
-                # datastore does all inheritance on course load.
-                #child.inherit_metadata(self.metadata)
                 self._child_instances.append(child)
 
         return self._child_instances
 
-
     def get_child_by_url_name(self, url_name):
         """
         Return a child XModuleDescriptor with the specified url_name, if it exists, and None otherwise.