private static function get_assignments_config_structure() {
        return new external_single_structure(
            array(
                'id' => new external_value(PARAM_INT, 'assign_plugin_config id', VALUE_OPTIONAL),
                'assignment' => new external_value(PARAM_INT, 'assignment id', VALUE_OPTIONAL),
                'plugin' => new external_value(PARAM_TEXT, 'plugin'),
                'subtype' => new external_value(PARAM_TEXT, 'subtype'),
                'name' => new external_value(PARAM_TEXT, 'name'),
                'value' => new external_value(PARAM_TEXT, 'value')
            ), 'assignment configuration object'
        );
    }