Remove serach by primary key since Django's ORM handles this for us.

notto/nottoapp/models.py

@@ -47,4 +47,4 @@ def get_parent(self):
         Get parent note
         '''
         if self.url_title is not None and self.parent_note is not None:
-            return Note.objects.get(pk=self.parent_note.id)
+            return self.parent_note