休眠。 删除未使用的条目

Question

I have a table looks which like this:

ID  USER_NAME ROOM_ID
 1  user1   13
 2  user2   11  
 3  user3   null
 4  user4   4   
 5  user5   2   

And Room table

ID  ROOM_NAME SQUARE
13  room1   17
 4  room2   42  
 2  room3   26
11  room4   37  
 5  room5   28  

In my application i can change User's ROOM_ID, for example, for Null. And after this, i'll have a one "Unused" room (There's no user in this room).

So, the question is: How can i delete this room automaticly using Hibernate?

Thanks!

Answer 1

you can use a trigger for that:

CREATE OR REPLACE FUNCTION delete_room()
  RETURNS trigger AS
$BODY$
BEGIN
 DELETE FROM ROOMS WHERE (OLD.ROOM_ID = ID)
 RETURN NEW;
END;
$BODY$


CREATE TRIGGER delete_room_changed
  BEFORE UPDATE
  ON USERS
  FOR EACH ROW
  EXECUTE PROCEDURE delete_room()

that way when you update any user the assigned room is deleted

Answer 2

Try this code - see the comments for details:

Session session = null;
if(session == null) {
    initTransaction();
}

Room room = (Room) session.createCriteria(UserRoomTable.class); // First table Pojo class name
room.add(Restrictions.isNull("roomId"));
session.delete(room); // This deletes the unused entry