Hibernate关联关系之——单向n-1

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1 .单向 n-1 关联只需从n的一端可以访问1的一端

2.域模型: 从Order到Customer的多对一单向关联需要在Order类中定义一个Customer属性,而在Customer类中无需定义存放Order对象的集合属性

3.关系数据模型:ORDERS表中的CUSTOMER_ID参照CUSTOMER表的主键

测试代码：

1.Customer实体类和Order实体类

package com.elgin.hibernate.nto1;public class Customer {   private int customerId;private String customerName;public int getCustomerId() {return customerId;}public void setCustomerId(int customerId) {this.customerId = customerId;}public String getCustomerName() {return customerName;}public void setCustomerName(String customerName) {this.customerName = customerName;}}

package com.elgin.hibernate.nto1;public class Order {   private int orderId;private String orderName;private Customer customer;public int getOrderId() {return orderId;}public void setOrderId(int orderId) {this.orderId = orderId;}public String getOrderName() {return orderName;}public void setOrderName(String orderName) {this.orderName = orderName;}public Customer getCustomer() {return customer;}public void setCustomer(Customer customer) {this.customer = customer;}}

2.2个实体类分别对应的hbm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 2015-9-21 20:58:02 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping>    <class name="com.elgin.hibernate.nto1.Customer" table="CUSTOMERS">        <id name="customerId" type="int">            <column name="CUSTOMER_ID" />            <generator class="native" />        </id>        <property name="customerName" type="java.lang.String">            <column name="CUSTOMER_NAME" />        </property>    </class></hibernate-mapping>

<?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 2015-9-21 20:58:02 by Hibernate Tools 3.4.0.CR1 --><hibernate-mapping package="com.elgin.hibernate.nto1">    <class name="Order" table="ORDERS">        <id name="orderId" type="int">            <column name="ORDER_ID" />            <generator class="native" />        </id>        <property name="orderName" type="java.lang.String">            <column name="ORDER_NAME" />        </property>        <!--           映射多对一关联关系 使用many-to-one映射多对一关联关系          name：多这一端关联一的那一端的属性名          class：一那一端对应的类名          column：一那一端对应多的一端对应的数据表中字段的名字                                   -->        <many-to-one name="customer" class="Customer">            <column name="CUSTOMER_ID" />        </many-to-one>    </class></hibernate-mapping>

3.Junit单元测试类

        @Testpublic void testMany2OneSave(){Customer customer=new Customer();customer.setCustomerName("CC");Order order1=new Order();order1.setOrderName("order-5");order1.setCustomer(customer);Order order2=new Order();order2.setOrderName("order-6");order2.setCustomer(customer);//发出了3条insert语句//先插入1的一端，再插入n的一端，只有insert语句/*session.save(customer);session.save(order1);session.save(order2);*///发出了3条insert语句和2条update语句//先插入n的一端，再插入1的一端，要额外发出update语句，推荐使用第一种方式session.save(order1);session.save(order2);session.save(customer);}@Testpublic void testMany2OneGet(){//1.若查询的n的那一端的对象，默认情况下，只查询n的一端的对象，//2.它所关联的1的那一端的对象为代理对象，等到使用的时候才会发出sql语句查询对此代理对象进行初始化//3.如果在使用此对象时session已关闭，则会抛出懒加载异常LazyInitializationExceptionOrder order=(Order) session.get(Order.class, 1);System.out.println(order.getOrderName());System.out.println(order.getCustomer().getCustomerName());}@Testpublic void testMany2OneDelete(){//在不设定关联关系的前提下，如果1的一端有对象被n一端的对象引用，不能直接删除1一端的对象Customer customer=(Customer) session.get(Customer.class, 1);session.delete(customer);}

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