hibernate 之 关联映射的单向多对多

1. 在实际开发中，多对多关联比较常见，比如用户和角色，或者是角色和权限。

角色和权限的关系如图：

2. 类结构：Permission.java

public class Permission {
    private int id;
    private String name;
    public Permission() {
        // TODO Auto-generated constructor stub
    }
    
    public Permission(String name) {
        super();
        this.name = name;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Role.java

public class Role {
    private int id;
    private String name;
    private Set<Permission> permissions=new HashSet<Permission>();
    public Role() {
        // TODO Auto-generated constructor stub
    }
    
    public Role(String name) {
        super();
        this.name = name;
    }

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set<Permission> getPermissions() {
        return permissions;
    }
    public void setPermissions(Set<Permission> permissions) {
        this.permissions = permissions;
    }
}

3. 映射文件：

Permission.hbm.xml

<hibernate-mapping>
    <class name="cn.wh.vo.Permission" table="t_permission">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name"/>
    </class>
</hibernate-mapping>

Role.hbm.xml

<hibernate-mapping package="cn.wh.vo">
    <class name="Role" table="t_role">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name"/>
        <!-- table表示 关联表  这张表由hibernate来创建和维护-->
        <set name="permissions" table="t_role_permission">
            <!-- 当前类在关联表中的外键 -->
            <key column="rid"></key>
            <!-- 表示当前类的关联类在关联表中的外键 -->
            <many-to-many column="pid" class="Permission"/>
        </set>
    </class>
</hibernate-mapping>

4. 测试：

public class HibernateTest {
    private Session session=null;
    @Before
    public void setUp(){
        session = HibernateUtil.getSession();
    }
    @After
    public void tearDown(){
        HibernateUtil.close();
    }
    @Test
    public void testCreateDB(){
        Configuration cfg = new Configuration().configure();
        SchemaExport export = new SchemaExport(cfg);
        //第一个参数  是否打印  数据库脚本
        //第二个参数 是否将脚本导入数据库执行
        export.create(true, true);
    }
    @Test
    public void testInit(){
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            Role r1 = new Role("管理员");
            Role r2 = new Role("会员");
            Permission p1 = new Permission("系统管理");
            Permission p2 = new Permission("用户管理");
            Permission p3 = new Permission("订单管理");
            Permission p4 = new Permission("商品管理");
            r1.getPermissions().add(p1);
            r1.getPermissions().add(p2);
            r1.getPermissions().add(p3);
            r1.getPermissions().add(p4);
            r2.getPermissions().add(p3);
            r2.getPermissions().add(p4);
            session.save(p1);
            session.save(p2);
            session.save(p3);
            session.save(p4);
            session.save(r1);
            session.save(r2);
            tx.commit();
            
        } catch (Exception e) {
            if(tx!=null)
                tx.rollback();
        }
    }
    @Test
    public void testGet(){
        Role r = (Role)session.get(Role.class, 1);
        System.out.println(r.getName());
        System.out.println("--------------");
        for(Permission p:r.getPermissions()){
            System.out.println(p.getName());
        }
    }
    }