private function findPreviousUpdate($assignmentId)
{
$previousAssignmentIdCached = Cache::get('previous_assignment_id_for_' . $assignmentId);
if ($previousAssignmentIdCached !== null) {
return $previousAssignmentIdCached;
} else {
$ascUpdates = AssignmentUpdate::where('assignment_id', $assignmentId)->orderBy('created_at', 'DESC')->get()->last();
return $ascUpdates;
}
}