public function update_effective_access($userid) {

        $override = $this->override_exists($userid);

        // Merge with assign defaults.
        $keys = array('duedate', 'cutoffdate', 'allowsubmissionsfromdate');
        foreach ($keys as $key) {
            if (isset($override->{$key})) {
                $this->get_instance()->{$key} = $override->{$key};
            }
        }

    }