Add Node._check_node_exists() calls to all Node methods, because nodes could have been deleted in between calls. Add Node.get_subscription(). Only fire deferred (with None) on success of Node.add_subscription(). Fix Node.set_configuration() to actually work and only update the Node objects configuration when the SQL query has succeeded. Implement Node.remove_subscription(). Implement Node.is_subscribed(). Implement LeafNode methods (unchecked!).