一个用户可以有多种角色
一个角色可以分配给多个用户
单从一边看，都是一对多的关系，但是放在一起就是多对多了.看代码吧。
单向关系：user一方持有Role一方的引用
Role.java
package com.ahuzl.hibernate;
public class Role {
private int id;
private String name;
。。。省略 get set方法
}
Role.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.ahuzl.hibernate">
<class name="Role" table="t_role">
<id name="id" column="role_id">
<generator class="native"/>
</id>
<property name="name" column="role_name"/>
</class>
</hibernate-mapping>
User.java
package com.ahuzl.hibernate;
import java.util.Set;
public class User {
private int id;
private String name;
private Set role;
。。。省略 get set方法
}
User.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.ahuzl.hibernate.User" table="t_user" >
<id name="id" column="user_id">
<generator class="native"/>
</id>
<property name="name" column="user_name"/>
<set name="role" table="t_user_role">
<key column="user_id"/>
<many-to-many class="com.ahuzl.hibernate.Role" column="role_id"/>
</set>
</class>
</hibernate-mapping>
特别的地方就在这里了，table="t_user_role"会生成一个中间表，表中的字段为<set></set>
标签中配置的字段。
<key column="user_id"/> ： 来自自己对象内部的属性
<many-to-many class="com.ahuzl.hibernate.Role" column="role_id"/> ： 来自其他对象的属性，所以要写清楚对象的类名
保存
public class Many2ManyTest extends TestCase {
public void testSave(){
Session session = null;
try{
session = HibernateUtils.getSession();
session.beginTransaction();
//保存三个角色，技术者，reader，manager
Role role1 = new Role();
role1.setName("技術者");
session.save(role1);
Role role2 = new Role();
role2.setName("リーダー");
session.save(role2);
Role role3 = new Role();
role3.setName("マネージャ");
session.save(role3);
User user1 = new User();
user1.setName("陣野");
Set roleOfUser1 = new HashSet();
roleOfUser1.add(role1);
user1.setRole(roleOfUser1);
session.save(user1);
//保存用户，并给其分配相应的权限
User user2 = new User();
user2.setName("幸島");
Set roleOfUser2 = new HashSet();
roleOfUser2.add(role1);
roleOfUser2.add(role2);
user2.setRole(roleOfUser2);
session.save(user2);
User user3 = new User();
user3.setName("桑田");
Set roleOfUser3 = new HashSet();
roleOfUser3.add(role3);
user3.setRole(roleOfUser3);
session.save(user3);
session.getTransaction().commit();
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
if (session != null){
if (session.isOpen()){
session.close();
}
}
}
}
}
查询
public void testLoad(){
Session session = null;
try{
session = HibernateUtils.getSession();
session.beginTransaction();
User user = (User)session.get(User.class, 2);
System.out.println("userId : " + user.getId());
System.out.println("userName : " + user.getName());
//迭代输出id为2的用户的角色
Set roleOfUser = user.getRole();
Iterator it = roleOfUser.iterator();
while(it.hasNext()){
Role role = (Role)it.next();
System.out.println("user's Role : " + role.getName());
}
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
if (session != null){
if (session.isOpen()){
session.close();
}
}
}
}
双向即为：各自持有对方的引用
改变的地方不大，只在Role.java中加入了User的引用，还有在Role.hbm.xml中加入了User属性如下：
Role.java
package com.ahuzl.hibernate;
import java.util.Set;
public class Role {
private int id;
private String name;
private Set user;
...省略 get set 方法
}
Role.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.ahuzl.hibernate">
<class name="Role" table="t_role">
<id name="id" column="role_id">
<generator class="native"/>
</id>
<property name="name" column="role_name"/>
<set name="user" table="t_user_role">
<key column="role_id"></key>
<many-to-many class="User" column="user_id"/>
</set>
</class>
</hibernate-mapping>
这里<set标签的写法和单向时一样，table="t_user_role"注意要一致，还有key 和many-to-many的column,别写错就行了。
还有一点关于结果的排序，如果配置了，那么hibernate会为我们排序，升序默认或esc，降序desc
<set name="user" table="t_user_role" order-by="user_id desc">
<key column="role_id"/>
<many-to-many class="User" column="user_id"/>
</set>
如上面的配置，hibernate会在SQL中加入order by XXX desc
保存不会有任何改变，只是先保存谁都无所谓了，
查询
public class Many2ManyTest extends TestCase {
public void testLoad2(){
Session session = null;
try{
session = HibernateUtils.getSession();
session.beginTransaction();
Role role = (Role)session.load(Role.class, 1);
System.out.println("roleId : " + role.getId());
System.out.println("roleName : " + role.getName());
//迭代输出id为1的角色的用户
Set roleOfUser = role.getUser();
Iterator it = roleOfUser.iterator();
while(it.hasNext()){
User user = (User)it.next();
System.out.println("userID : " + user.getId());
System.out.println("userName: " + user.getName());
}
}catch(Exception e){
e.printStackTrace();
session.getTransaction().rollback();
}finally{
if (session != null){
if (session.isOpen()){
session.close();
}
}
}
}
}