pmgr/site/models/membership.php

<?php
class Membership extends AppModel {

  var $belongsTo =
    array('User',
	  'Site',
	  'Group'
	  );

  function memberGroups($user_id, $site_id) {
    $this->prEnter(compact('user_id', 'site_id'));

    $this->cacheQueries = true;
    $groups = $this->find('all', array
			  ('recursive' => -1,
			   'fields' => array('group_id'),
			   'conditions' => array(array('user_id' => $user_id),
						 array('site_id' => $site_id)),
			   ));
    $this->cacheQueries = false;

    if (empty($groups))
      return $this->prReturn(null);

    $group_ids = array();
    foreach ($groups AS $group)
      $group_ids[] = $group['Membership']['group_id'];

    return $this->prReturn($group_ids);
  }

  function memberOf($user_id, $site_id) {
    $groups = $this->memberGroups($user_id, $site_id);
    return (!empty($groups));
  }

}