hibernate框架多对多（十七）

用户和角色是多对多的关系。那么他们需要一个中间表来维持多对多的关系。中间表有两个外键分别指向用户表和角色表的主键。中间没有单独的主键，uid和rid作为联合主键。

如果我们自己创建，就要创建三张表。

如果使用hibernate，只要编写2个javabean，编写2个映射的配置文件，中间表会自动生成。

一、javabean和配置

1.1 javabean

User.java

package com.hib.domain;import java.util.HashSet;import java.util.Set;public class User {private Long uid;private String username;private String password;//多对多，编写的都是集合，集合要自己new哦private Set<Role> roles = new HashSet<>();public Long getUid() {return uid;}public void setUid(Long uid) {this.uid = uid;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public Set<Role> getRoles() {return roles;}public void setRoles(Set<Role> roles) {this.roles = roles;}}

Role.java

package com.hib.domain;import java.util.HashSet;import java.util.Set;public class Role {private Long rid;private String rname;//多对多，编写的都是集合，集合要自己new哦private Set<User> users = new HashSet<>();public Long getRid() {return rid;}public void setRid(Long rid) {this.rid = rid;}public String getRname() {return rname;}public void setRname(String rname) {this.rname = rname;}public Set<User> getUsers() {return users;}public void setUsers(Set<User> users) {this.users = users;}}

1.2 配置

User.hbm2.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping><class name="com.hib.domain.User" table="sys_user"><id name="uid" column="uid"><generator class="native" /></id><property name="username" column="username" /><property name="password" column="password" /><!-- 只要javabean中有集合，在配置中就要配 --><!-- 配置多对多: name——集合的名称; table——中间表的名称 --><set name="roles" table="sys_user_role"><!-- 当前表在中间表的外键的名称 --><key column="uid" /><!-- class——集合中存入对象，对象的全路径；column——集合中对象在中间表的外键的名称 --><many-to-many class="com.hib.domain.Role" column="rid" /></set></class></hibernate-mapping>    

Role.hbm2.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-mapping PUBLIC     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping><class name="com.hib.domain.Role" table="sys_role"><id name="rid" column="rid"><generator class="native" /></id><property name="rname" column="rname" /><!-- 多对多必须有一方放弃外键的维护，建议，哪方操作少，就在哪方放弃 --><set name="users" table="sys_user_role" inverse="true"><key column="rid" /><many-to-many class="com.hib.domain.User" column="uid" /></set></class></hibernate-mapping>  

二、测试程序

package com.hib.utils;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;/** * hibernate框架的工具类 * */public class HibernateUtils {private static final Configuration CONFIG;private static final SessionFactory FACTORY;// 静态代码块，类在加载的时候就会执行static {// 加载xml的配置文件CONFIG = new Configuration().configure();// 构造工厂FACTORY = CONFIG.buildSessionFactory();}public static Session getSession() {return FACTORY.openSession();}/** * 业务层开事务，就用这个 *  * @return */public static Session getCurrentSession() {// 从ThreadLocal类中获取到session对象return FACTORY.getCurrentSession();}public static void main(String[] args) {getSession();}}

执行main方法

三、运行结果

四、保存程序

@Testpublic void run1() {Session session = HibernateUtils.getCurrentSession();Transaction tx = session.beginTransaction();// 模拟多对多，双向的关联// 创建用户User u1 = new User();u1.setUsername("zhangsan");User u2 = new User();u2.setUsername("lisi");// 创建角色Role r1 = new Role();r1.setRname("manager");Role r2 = new Role();r2.setRname("actor");// 关联u1.getRoles().add(r1);u1.getRoles().add(r2);r1.getUsers().add(u1);r2.getUsers().add(u1);u2.getRoles().add(r1);r1.getUsers().add(u2);session.save(u1);session.save(u2);session.save(r1);session.save(r2);tx.commit();}

五、保存结果

看sql：

log4j:WARN No appenders could be found for logger (org.jboss.logging).log4j:WARN Please initialize the log4j system properly.log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.Hibernate:     insert     into        sys_user        (username, password)     values        (?, ?)Hibernate:     insert     into        sys_user        (username, password)     values        (?, ?)Hibernate:     insert     into        sys_role        (rname)     values        (?)Hibernate:     insert     into        sys_role        (rname)     values        (?)Hibernate:     insert     into        sys_user_role        (uid, rid)     values        (?, ?)Hibernate:     insert     into        sys_user_role        (uid, rid)     values        (?, ?)Hibernate:     insert     into        sys_user_role        (uid, rid)     values        (?, ?)

源码下载