OphTrOperationbooking_Operation_Date_Letter_Sent::rules PHP Method

    public function rules()
    {
        // NOTE: you should only define rules for those attributes that
        // will receive user inputs.
        return array(array('id, element_id, date_invitation_letter_sent, date_1st_reminder_letter_sent, date_2nd_reminder_letter_sent, date_gp_letter_sent, date_scheduling_letter_sent', 'safe', 'on' => 'search'));
    }