Hibernate入门04_双向多对一

来源：互联网发布：玛雅动漫制作软件编辑：程序博客网时间：2024/06/06 11:02

这里还是以顾客和订单之间的关系来说明，一个客户可以有多个订单，但是一个订单只能对应一个客户；

1、项目的目录结构
这里写图片描述

2、Customer.java

import java.util.HashSet;import java.util.Set;/**客户-可以有多个 */public class Customer {    private Integer customerId;    private String customerName;    /**需要把集合初始化防止发生null指针异常*/    private Set<Order> orders = new HashSet<>();    //get/set...}

Customer.hbm.xml映射文件

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!-- Generated 2017-3-25 18:05:11 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping package="com.hibernate.entities.n21both">    <class name="Customer" table="CUSTOMERS">        <id name="customerId" type="java.lang.Integer">            <column name="CUSTOMER_ID" />            <generator class="native" />        </id>        <property name="customerName" type="java.lang.String">            <column name="CUSTOMER_NAME" />        </property>        <!-- 映射一对多的集合映射 set的三个属性： inverse="true":放弃维护关联关系，让Order来维护， cascade="delete":设置级联关系删除             ， cascade="delete-orphan"；开发是不建议设置cascade，建议手动删除 order-by:在查询时对集合中的元素进行排序 -->        <set name="orders" table="ORDERS" inverse="true" order-by="ORDER_NAME DESC">            <key column="CUSTOMER_ID"></key>            <one-to-many class="Order" />        </set>    </class></hibernate-mapping>

3、Order.java

public class Order {    private Integer orderId;    private String orderName;    private Customer customer;    //set/get...}

Order.hbm.xml映射文件

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!-- Generated 2017-3-25 18:05:11 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping package="com.hibernate.entities.n21both">    <class name="Order" table="ORDERS">        <id name="orderId" type="java.lang.Integer">            <column name="ORDERID" />            <generator class="native" />        </id>        <property name="orderName" type="java.lang.String">            <column name="ORDER_NAME" />        </property>        <!-- 映射多对一的关联关系  使用多对一的关联关系 -->        <many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one>    </class></hibernate-mapping>

4、hibernate.cfg.xml配置文件

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE hibernate-configuration PUBLIC        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><hibernate-configuration>    <session-factory>    <!-- 配置链接数据库的基本信息 -->        <property name="connection.username">root</property>        <property name="connection.password">root</property>        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate01</property>        <!-- hibernate的基本信息 -->        <!-- hibernate使用的数据库方言 -->        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>        <!-- 执行操作时是否在控制台打印sql语句 -->        <property name="show_sql">true</property>        <!-- 是否对sql进行格式化 -->        <property name="format_sql">true</property>        <!-- 指定自动生成数据表的策略 -->        <property name="hbm2ddl.auto">update</property>        <!-- 设置hibernate的隔离级别 -->        <property name="connection.isolation">2</property>        <!-- 删除对象后，设置其OID为null -->        <property name="use_identifier_rollback">true</property>        <!-- 配置C3P0数据源 -->        <property name="c3p0.max_size">100</property>        <property name="c3p0.min_size">5</property>        <property name="c3p0.acquire_increment">2</property>        <property name="c3p0.idle_test_period">2000</property>        <property name="c3p0.timeout">2000</property>        <property name="c3p0.max_statements">10</property>        <!-- 设置JDBC的statement读取数据库的时候每次从数据库中读取记录条数，这个值100合适，太大会损耗内存，小了速度慢 -->        <property name="jdbc.fetch_size">100</property>        <!-- 设置数据库进行批量删除，更新，插入的时候批次的大小，30比较合适 -->        <property name="jdbc.batch_size">30</property>        <!-- 指定关联的hbm.xml文件 -->        <mapping resource="com/hibernate/entities/n21both/Order.hbm.xml"/>        <mapping resource="com/hibernate/entities/n21both/Customer.hbm.xml"/>    </session-factory></hibernate-configuration>

5、Test测试

import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.hibernate.service.ServiceRegistryBuilder;import org.junit.After;import org.junit.Before;import org.junit.Test;import com.hibernate.entities.n21both.Customer;import com.hibernate.entities.n21both.Order;public class HibernateTest {    private SessionFactory sessionFactory;    private Session session;    private Transaction transaction;    @Test    public void testOne2ManySave() {        Customer customer = new Customer();        customer.setCustomerName("AA");        Order order1 = new Order();        order1.setOrderName("Oyder1");        Order order2 = new Order();        order2.setOrderName("Oyder2");        // 设定关联关系        order1.setCustomer(customer);        order2.setCustomer(customer);        customer.getOrders().add(order1);        customer.getOrders().add(order2);        // 三条insert两条update        session.save(customer);        session.save(order1);        session.save(order2);        // 三条insert，4条update        // session.save(order1);        // session.save(order2);        // session.save(customer);    }    @Test    public void testOne2ManyGet() {        // 对多的一端采用延迟加载        Customer customer = (Customer) session.get(Customer.class, 1);        System.out.println(customer.getCustomerName());        System.out.println(customer.getOrders().getClass());    }    @Test    public void testOne2ManyDelete(){        //设定级联 cascade="delete":设置级联关系删除关系后，可以删除        Customer customer = (Customer) session.get(Customer.class, 1);        session.delete(customer);    }    @Test    public void testCascade_Orphan(){        //设定级联 cascade="delete-orphan":设置级联关系删除关系后，可以删除        Customer customer = (Customer) session.get(Customer.class, 2);        customer.getOrders().clear();//      session.delete(customer);    }    @Before    public void init() {        System.out.println("HibernateTest.init()");        // 1.创建一个sessionFactory对象        Configuration configuration = new Configuration().configure();        ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties())                .buildServiceRegistry();        sessionFactory = configuration.buildSessionFactory(serviceRegistry);        // 2.创建一个session对象        session = sessionFactory.openSession();        // 3.开启事务        transaction = session.beginTransaction();    }    @After    public void destroy() {        System.out.println("HibernateTest.destroy()");        // 5.提交事务        transaction.commit();        // 6.关闭session        session.close();        // 7.关闭SessionFactory        sessionFactory.close();    }}

6、备注：本博客适合有一定java基础，对数据库有一定认识的读者。不会做过多的文字描述，敬请原谅。本人也是新手，写博客当做笔记作分享，不喜勿喷，欢迎指教。

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