Hibernate 多对多例

create table tgroup (
  group_id int not null auto_increment,
  name varchar(16) not null default '',
  primary key  (group_id)
) type=innodb;
create table trole (
  role_id int not null auto_increment,
  name varchar(16) not null default '', 
  primary key  (role_id)
) type=innodb;
create table tgroup_role (
  group_id int not null,
  role_id int not null,
  primary key(group_id, role_id),
  index (group_id),
  foreign key (group_id) references tgroup(group_id),
  index (role_id),
  foreign key (role_id) references trole(role_id)
) type=innodb;

package ivan.hibernate.many2many;
public class Group {
   private int id;
   private String name;
   private Set roles = new HashSet();
   ...
}

Group.hbm.xml

<hibernate-mapping>
    <class name="ivan.hibernate.many2many.Group" table="tgroup">
        <id name="id" column="group_id" unsaved-value="0">
            <generator class="increment"/>
        </id>
        <property name="name" type="string"/>      
        <set name="roles" table="tgroup_role" cascade="save-update">            
             <key column="group_id"/>
             <many-to-many class="ivan.hibernate.many2many.Role" column="role_id"/>
        </set>
    </class>
</hibernate-mapping>

package ivan.hibernate.many2many;
public class Role {
   private int id;
   private String name;
   private Set groups = new HashSet();
   ...
}

Role.hbm.xml：

<hibernate-mapping>
    <class name="ivan.hibernate.many2many.Role" table="trole">
        <id name="id" column="role_id" unsaved-value="0">
            <generator class="increment"/>
        </id>
        <property name="name" type="string"/>      
        <set name="groups" table="tgroup_role" inverse="true" cascade="save-update">            
             <key column="role_id"/>
             <many-to-many class="ivan.hibernate.many2many.Group" column="group_id"/>
        </set>
    </class>
</hibernate-mapping>