protected function saveAssignments()
    {
        $assignmentData = [];
        foreach ($this->assignments as $userId => $assignments) {
            foreach ($assignments as $name => $assignment) {
                /* @var $assignment Assignment */
                $assignmentData[$userId][] = $assignment->roleName;
            }
        }
        $this->saveToFile($assignmentData, $this->assignmentFile);
    }