PHP：总结用户的对象

I have a module in CMSmadesimple which makes 'registrations'. A registration is a class in php with id user and registerstatus.

How can I summarize all users (not just the ones who have a registration) and afther them if they are registrated or not.

the class (nb_persons is used as registration status)

class EventsManager_registration
{
    protected $table = 'events_registrations';

    protected $custom_fields = array(
        'id_event'=>'',
        'id_user'=>'',
        'nb_persons'=>0,
        'dr_reden'=>''
    );

I know how to summarize the events foreach from=$registrations item='registration' but I want to summarize my users with their registration or not