Normalize the representation of Scope.content data in MongoModulestore FieldData

Without this, the new 'items' field in the course_info xmodule caused
bizarre behavior. If you added the text 'items' to a course_info
section, then the LMS would throw a 500, because the field name isn't
'data', but the stored data is a string, leading to the check of
`key.field_name in self._data`, where key.field_name is the string 'items',
and self._data is the content string.

common/lib/xmodule/xmodule/html_module.py

@@ -229,7 +229,7 @@ class AboutFields(object):
     )
     data = String(
         help="Html contents to display for this module",
-        default="",
+        default=u"",
         scope=Scope.content
     )
 
@@ -263,7 +263,7 @@ class StaticTabFields(object):
         default="Empty",
     )
     data = String(
-        default=textwrap.dedent("""\
+        default=textwrap.dedent(u"""\
             <p>This is where you can add additional pages to your courseware. Click the 'edit' button to begin editing.</p>
         """),
         scope=Scope.content,
@@ -300,7 +300,7 @@ class CourseInfoFields(object):
     )
     data = String(
         help="Html contents to display for this module",
-        default="<ol></ol>",
+        default=u"<ol></ol>",
         scope=Scope.content
     )
 

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

@@ -60,7 +60,10 @@ class MongoKeyValueStore(InheritanceKeyValueStore):
     """
     def __init__(self, data, children, metadata):
         super(MongoKeyValueStore, self).__init__()
-        self._data = data
+        if not isinstance(data, dict):
+            self._data = {'data': data}
+        else:
+            self._data = data
         self._children = children
         self._metadata = metadata
 
@@ -72,10 +75,7 @@ class MongoKeyValueStore(InheritanceKeyValueStore):
         elif key.scope == Scope.settings:
             return self._metadata[key.field_name]
         elif key.scope == Scope.content:
-            if key.field_name == 'data' and not isinstance(self._data, dict):
-                return self._data
-            else:
-                return self._data[key.field_name]
+            return self._data[key.field_name]
         else:
             raise InvalidScopeError(key)
 
@@ -85,10 +85,7 @@ class MongoKeyValueStore(InheritanceKeyValueStore):
         elif key.scope == Scope.settings:
             self._metadata[key.field_name] = value
         elif key.scope == Scope.content:
-            if key.field_name == 'data' and not isinstance(self._data, dict):
-                self._data = value
-            else:
-                self._data[key.field_name] = value
+            self._data[key.field_name] = value
         else:
             raise InvalidScopeError(key)
 
@@ -99,9 +96,7 @@ class MongoKeyValueStore(InheritanceKeyValueStore):
             if key.field_name in self._metadata:
                 del self._metadata[key.field_name]
         elif key.scope == Scope.content:
-            if key.field_name == 'data' and not isinstance(self._data, dict):
-                self._data = None
-            else:
+            if key.field_name in self._data:
                 del self._data[key.field_name]
         else:
             raise InvalidScopeError(key)
@@ -112,10 +107,7 @@ class MongoKeyValueStore(InheritanceKeyValueStore):
         elif key.scope == Scope.settings:
             return key.field_name in self._metadata
         elif key.scope == Scope.content:
-            if key.field_name == 'data' and not isinstance(self._data, dict):
-                return True
-            else:
-                return key.field_name in self._data
+            return key.field_name in self._data
         else:
             return False
 
@@ -640,6 +632,10 @@ class MongoModuleStore(ModuleStoreWriteBase):
         # layer but added it here to enable quick conversion. I'll need to reconcile these.
         if metadata is None:
             metadata = {}
+
+        if definition_data is None:
+            definition_data = {}
+
         if system is None:
             services = {}
             if self.i18n_service:
@@ -658,11 +654,6 @@ class MongoModuleStore(ModuleStoreWriteBase):
                 services=services,
             )
         xblock_class = system.load_block_type(location.category)
-        if definition_data is None:
-            if hasattr(xblock_class, 'data') and xblock_class.data.default is not None:
-                definition_data = xblock_class.data.default
-            else:
-                definition_data = {}
         dbmodel = self._create_new_field_data(location.category, location, definition_data, metadata)
         xmodule = system.construct_xblock_from_class(
             xblock_class,
@@ -796,8 +787,6 @@ class MongoModuleStore(ModuleStoreWriteBase):
         """
         try:
             definition_data = xblock.get_explicitly_set_fields_by_scope()
-            if len(definition_data) == 1 and 'data' in definition_data:
-                definition_data = definition_data['data']
             payload = {
                 'definition.data': definition_data,
                 'metadata': own_metadata(xblock),

common/lib/xmodule/xmodule/modulestore/tests/test_mongo.py

@@ -299,7 +299,7 @@ class TestMongoKeyValueStore(object):
             assert_false(self.kvs.has(key))
 
     def test_read_non_dict_data(self):
-        self.kvs._data = 'xml_data'
+        self.kvs = MongoKeyValueStore('xml_data', self.children, self.metadata)
         assert_equals('xml_data', self.kvs.get(KeyValueStore.Key(Scope.content, None, None, 'data')))
 
     def _check_write(self, key, value):
@@ -312,7 +312,7 @@ class TestMongoKeyValueStore(object):
         yield (self._check_write, KeyValueStore.Key(Scope.settings, None, None, 'meta'), 'new_settings')
 
     def test_write_non_dict_data(self):
-        self.kvs._data = 'xml_data'
+        self.kvs = MongoKeyValueStore('xml_data', self.children, self.metadata)
         self._check_write(KeyValueStore.Key(Scope.content, None, None, 'data'), 'new_data')
 
     def test_write_invalid_scope(self):