Element_Query::parse_join()

	protected function parse_join() {
		$join = parent::parse_join();

		if ( ! empty( $this->query_vars['form_id'] ) ) {
			$table_name = $this->manager->get_table_name();
			$container_table_name = $this->manager->get_parent_manager( 'containers' )->get_table_name();

			$join .= " INNER JOIN %{$container_table_name}% ON ( %{$table_name}%.container_id = %{$container_table_name}%.id )";
		}

		return $join;
	}