private function findMembershipsByUserId($user_id, $semester)
{
$memberships = \SimpleORMapCollection::createFromArray(\CourseMember::findBySQL('user_id = ? ORDER BY mkdate ASC', array($user_id)));
// filter by semester
if ($semester) {
$memberships = $memberships->filter(function ($m) use($semester) {
$course = $m->course;
return $course->start_time == $semester->beginn || $course->start_time <= $semester->beginn && ($course->duration_time == -1 || $semester->beginn <= $course->end_time);
});
}
return $memberships;
}
