@davihu
Thanx, it works, but still it does not work like i need. :)
Here is my code:
    $this->validate(
     new Uniqueness(
                                    array(
                                            "field"   => "room_number",
                                            "field"   => "start_date",
                                            "field"   => "event_time",  
                                    "message" => "This appt is already scheduled. Please choose another Room, Date or Time"
                                    )
                    )
                          );
     if ($this->validationHasFailed() == true) 
     {
                return false;
          }
But i want it to work only if all 3 fields are indentical to the previous records. Can you advise? Thnx