Dot-Notation: x._id = ObjectId() doesn't seem to work properly

For whatever reason, this does not work as expected:
	entry._id = ObjectId()
Need to go this way:
	entry['_id'] = ObjectId()

mediagoblin/submit/views.py

@@ -52,7 +52,7 @@ def submit_start(request):
 
             # create entry and save in database
             entry = request.db.MediaEntry()
-            entry._id = ObjectId()
+            entry['_id'] = ObjectId()
             entry['title'] = (
                 unicode(request.POST['title'])
                 or unicode(splitext(filename)[0]))