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
@Test
public 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);
} @Test
public 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LazyInitializationException
Order order=(Order) session.get(Order.class, 1);
System.out.println(order.getOrderName());
System.out.println(order.getCustomer().getCustomerName());
}
@Test
public 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);
}