技术分析之Hibernate的关联关系映射之一对多映射

实际开发中往往需要利用和建立一对多的表，比如客户和订单的关系，一个客户可以建立多个订单，一个订单只能被一个客户生成，所以就生成了一对多的关系，下面就来演示下配置和代码。

客户User类

package model;import java.util.HashSet;import java.util.Set;public class User {private Long uid;private String uname;private String upwd;//对应的多表类应该用set集合，而且要初始化，否则会空指针异常private Set<Order> orders = new HashSet<>();public Long getUid() {return uid;}public void setUid(Long uid) {this.uid = uid;}public String getUname() {return uname;}public void setUname(String uname) {this.uname = uname;}public String getUpwd() {return upwd;}public void setUpwd(String upwd) {this.upwd = upwd;}public Set<Order> getOrders() {return orders;}public void setOrders(Set<Order> orders) {this.orders = orders;}@Overridepublic String toString() {return "User [uid=" + uid + ", uname=" + uname + ", upwd=" + upwd + "]";}public User(Long uid, String uname, String upwd, Set<Order> orders) {super();this.uid = uid;this.uname = uname;this.upwd = upwd;this.orders = orders;}public User() {super();}}

订单Order类

package model;public class Order {private Long oid;private String oname;private Double oprice;private User user;public Long getOid() {return oid;}public void setOid(Long oid) {this.oid = oid;}public String getOname() {return oname;}public void setOname(String oname) {this.oname = oname;}public Double getOprice() {return oprice;}public void setOprice(Double oprice) {this.oprice = oprice;}public User getUser() {return user;}public void setUser(User user) {this.user = user;}@Overridepublic String toString() {return "Order [oid=" + oid + ", oname=" + oname + ", oprice=" + oprice + "]";}public Order(Long oid, String oname, Double oprice, User user) {super();this.oid = oid;this.oname = oname;this.oprice = oprice;this.user = user;}public Order() {super();}}

User.hbm.xml的配置

<?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="model.User" table="user"><id name="uid"><generator class="native"></generator></id><property name="uname"></property><property name="upwd"></property><!-- set 配置在一方：表示一个集合    set name：name是一方中的set<多方>的属性名    key：表中的 外键名  column外键名            one-to-many class:配置的是多方的权限定名    cascade="save-update" ：级联保存        cascade="save-update,delete":级联删除  和级联更新     就相当于写个all:all就包括级联更新级联删除        cascade="delete-orphan":孤儿删除        一对多关系：一方默认是维护关键关系  inverse="false"：维护外键    inverse:反转的意思 是否把维护外键的活交给对方处理        一对多可以不用放弃外键维护  但是多对多必须要有一方来放弃对外键的维护。     --><set name="orders" cascade="all-delete-orphan"><key column="uid"></key><one-to-many class="model.Order" /></set></class></hibernate-mapping>

Order.hbm.xml的配置

<?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="model.Order" table="order1"><id name="oid"><generator class="native"></generator></id><property name="oprice"></property><property name="oname"></property><!-- 多方还要配置一方的对象属性    many-to-one:用来配置在多方的  一方的属性    name:多方中的一方的属性名    column:外键名     --><many-to-one name="user" column="uid" class="model.User" cascade="save-update"></many-to-one></class></hibernate-mapping>

hibernate.cfg.xml配置只需要安装基本配置然后加上对应的

<mapping resource="model/User.hbm.xml"/><mapping resource="model/Order.hbm.xml"/>

就可以了。

然后demo来操作一对多表的操作

HibernateUtile的代码

package utils;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class HibernateUtil {private static final Configuration cfg;private static final SessionFactory factory;static {cfg = new Configuration().configure();factory = cfg.buildSessionFactory();// 当jvm虚拟机被关闭的时候会走该方法Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {public void run() {factory.close();System.out.println("factory被关闭");}}));}public static Session openSession() {return factory.openSession();}}

test类

package test;import org.hibernate.Session;import org.hibernate.Transaction;import org.junit.Test;import model.Order;import model.User;import utils.HibernateUtil;//操作一对多的关系public class demo1 {@Testpublic void run1() {Session session = HibernateUtil.openSession();Transaction ts = session.beginTransaction();User user = new User();user.setUname("小李");user.setUpwd("2333");Order order = new Order();Order order2 = new Order();order.setOname("货物1");order.setOprice(12.6);order2.setOname("货物2");order2.setOprice(10.8);user.getOrders().add(order);user.getOrders().add(order2);session.save(user);//因为设置了级联更新，所以只需要保存user就可以，//session.save(order2);//session.save(order);ts.commit();session.close();}//效果和run1相同@Testpublic void run2() {Session session = HibernateUtil.openSession();Transaction ts = session.beginTransaction();User user = new User();user.setUname("小李");user.setUpwd("2333");Order order = new Order();Order order2 = new Order();order.setOname("货物1");order.setOprice(12.6);order2.setOname("货物2");order2.setOprice(10.8);order.setUser(user);order2.setUser(user);//因为设置了级联更新，所以只需要保存order就可以，//session.save(user);session.save(order2);session.save(order);ts.commit();session.close();}/* * hibernate在是默认可以删除一方的，但是多方会把外键置为null * 级联删除，删除一方的时候，去级联删除多方 *  * *///级联删除@Testpublic void run3() {Session session = HibernateUtil.openSession();Transaction ts = session.beginTransaction();User user = session.get(User.class, 1L);session.delete(user);ts.commit();session.close();}@Testpublic void run4() {Session session = HibernateUtil.openSession();Transaction ts = session.beginTransaction();Order order = session.get(Order.class, 1L);//只Schumacher了1订单，因为在Order.hbm.xml之配置了级联更新，没有配置级联删除session.delete(order);ts.commit();session.close();}/* * inverse="true"放弃对外键的维护，保存user的时候，order里面不会有外键 * delete-orphan孤儿删除，只要和父亲脱离关系，父亲杀死儿子（玩笑- -） * *///效果同run4@Testpublic void run5() {Session session = HibernateUtil.openSession();Transaction ts = session.beginTransaction();User user = session.get(User.class, 1L);Order order = session.get(Order.class, 1L);user.getOrders().remove(order);ts.commit();session.close();}}