<class name="com.foo.User" table="USERS">
        <id name="id" type="long" unsaved-value="null" column="id">
            <generator class="native"/>
        </id>

        <property name="name" type="string"/>

        <property name="password" type="string"/>

        <property name="email" type="string"/>

        <set name="groups" lazy="true" table="GROUP_USERS">
            <key column="user_id"/>
            <many-to-many class="com.foo.Group" column="group_id"/>
        </set>

    </class>

    <class name="com.foo.Group" table="GROUPS">
        <id name="id" type="long" unsaved-value="null" column="id">
            <generator class="native"/>
        </id>

        <property name="name" type="string"/>

        <property name="description" type="string"/>

        <set name="users" lazy="true" table="GROUP_USERS">
            <key column="group_id"/>
            <many-to-many class="com.foo.User" column="user_id"/>
        </set>

    </class>

        User user1 = new User();
        user1.setName("user1");
        user1.setPassword("password");
        user1.setEmail("user1@foo.com");
        sess.save(user1);

        User user2 = new User();
        user2.setName("user1");
        user2.setPassword("password");
        user2.setEmail("adam@foo.com");
        sess.save(user2);

        Group group1 = new Group();
        group1.setName("test group 1");
        group1.setDescription("test group 1 - description");
        sess.save(group1);

        Group group2 = new Group();
        group2.setName("test group 2");
        group2.setDescription("test group 2 - description");
        sess.save(group2);

        Query groupq = sess.createQuery("from com.foo.Group group");
        List groups = groupq.list();
        for (int i = 0; i < groups.size(); i++) {
            Group group = (Group) groups.get(i);
            log.debug("Found group: " + group.getName());

            Set userSet = group.getUsers();

            if (null == userSet) {
                userSet = new HashSet();
            }

            Query userq = sess.createQuery("from com.foo.User user");
            List users = userq.list();

            for (int j = 0; j < users.size(); j++) {
                User user = (User) users.get(j);
                log.debug("Adding user: " + user.getName() + " to group: " + group.getName());
                userSet.add(user);
            }

            group.setUsers(userSet);
            sess.saveOrUpdate(group);
            sess.flush();
        }

        Query userq = sess.createQuery("from com.foo.User user");
        List users = userq.list();
        for (int i = 0; i < users.size(); i++) {
            User user = (User) users.get(i);
            Set groups = user.getGroups();
            if (null == groups) {
                log.debug("user: " + user.getName() + " does not seem to be in any groups");
            }
            else {
                for (Iterator iterator = groups.iterator(); iterator.hasNext();) {
                    Group group = (Group) iterator.next();
                    log.debug("user: " + user.getName() + " is in group: " + group.getName());
                }
            }
        }