bidirectional many-to-many deleting

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

User and Role has a bidirectional many-to-many relationship,
both sides are mapped as cascade="save-update",one side is mapped as inverse="true",the other as inverse="false"

How should I delete a Role(or User) object,

Code:

Role role=(Role)session.load(Role.class,roleId);

session.delete(role);

OR

Code:

Role role=(Role)session.load(Role.class,roleId);

for(Iterator iter=role.getUsers().iterator();iter.hasNext();){
   ((User)iter.next()).getRoles().remove(role);
}

session.delete(role);

I think the second is the right one,but it is very prolix,and may be inefficient.

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

And I find that bidirectional many-to-many is very hard to maintain.

I write the following code to maintain a User's roles, it is very verbose.
Any good idea?

Code:

public static void modifyUserRoles(String userId, String[] roleIds) throws
        HibernateException {
        Session session = openSession();

        User user = (User) session.load(User.class, userId);

        int max = roleIds.length;
        Collection newRoles = new HashSet(max);
        for (int i = 0; i < max; i++) {
            newRoles.add(session.load(Role.class, roleIds[i]));
        }
        //----------------------------------------------------------------------
        //update roles the user no longer has
        for (Iterator iter = user.getRoles().iterator(); iter.hasNext(); ) {
            Role r = (Role) iter.next();
            if (!newRoles.contains(r)) {
                r.getUsers().remove(user);
            }
        }

        //update the user
        user.getRoles().retainAll(newRoles);
        user.getRoles().addAll(newRoles);
        //or just?
        //user.setRoles(newRoles);

        //update roles the user now has
        for (Iterator iter = newRoles.iterator(); iter.hasNext(); ) {
            Role r = (Role) iter.next();
            r.getUsers().add(user);
        }
        //----------------------------------------------------------------------
    }

gavin · **Posted:** Fri Nov 14, 2003 4:21 am

It can be made a lot less verbose by adding helper methods like:

Code:

class Role {

   void removeUser(User user) {
      users.remove(user);
      user.getRoles().remove(this);
   }

   void addUser(User user) {
      user.getRoles().add(this);
      users.add(user);
   }

}

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

yes,a little better.
but I think it is still inefficient, because lots of roles and their users must be loaded from the database.
bag may be more efficient than set in this case?

Code:

public static void modifyUserRole(String userId, String[] roleIds) throws
        HibernateException {
        Session session = null;
        //session=openSession();

        User user = (User) session.load(User.class, userId);

        int max = roleIds.length;
        Collection newRoles = new HashSet(max);
        for (int i = 0; i < max; i++) {
            newRoles.add(session.load(Role.class, roleIds[i]));
        }
        //----------------------------------------------------------------------
        for (Iterator iter = user.getRoles().iterator(); iter.hasNext(); ) {
            Role r = (Role) iter.next();
            if (!newRoles.contains(r)) {
                r.removeUser(user);
            }
        }

        for (Iterator iter = newRoles.iterator(); iter.hasNext(); ) {
            ( (Role) iter.next()).addUser(user);
        }
        //----------------------------------------------------------------------
}

yehs220 · **Joined:** Thu Aug 28, 2003 8:41 pm **Posts:** 17

bags may be worse,when mapped as inverse="false",they always delete all,and than insert.
is that true?

emmanuel · **Posted:** Fri Nov 14, 2003 6:52 am

Yes, see section 12 of the reference guide.
You can use idbag to solve this