映射多对一的关联关系用的是数据库的外键
如一个用户可以有多个订单
一的一端对象（用户）：
package chen;
//顾客
public class Customer {
private Integer customerId;
private String customerName;
public Integer getCustomerId() {
return customerId;
}
public void setCustomerId(Integer customerId) {
this.customerId = customerId;
}
public String getCustomerName() {
return customerName;
}
public void setCustomerName(String customerName) {
this.customerName = customerName;
}
}
多的一端对象（订单）
package chen;
//订单
public class Order {
private Integer orderId;
private String orderName;
private Customer customer;//用户外键
public Integer getOrderId() {
return orderId;
}
public void setOrderId(Integer 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;
}
}
配置文件
- 一的一端映射文件：
<hibernate-mapping>
<class name="chen.Customer" table="CUSTOMER">
<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>
</class>
</hibernate-mapping>
- 多的一端映射文件：
<hibernate-mapping>
<class name="chen.Order" table="ORDERS">
<id name="orderId" type="java.lang.Integer">
<column name="ORDER_ID" />
<generator class="native" />
</id>
<property name="orderName" type="java.lang.String">
<column name="ORDER_NAME" />
</property>
<!-- 映射多对一的关联关系 -->
<many-to-one name="customer" class="chen.Customer" column="CUSTOMER_ID">
</many-to-one>
</class>
</hibernate-mapping>
映射多对一在多端配置
使用many-to-one标签来 映射多对一的关联关系 name属性指向多端对象属性名 class一端对象全类名 column属性对应数据库列名
订单表
顾客表
保存到数据库
- 先保存一的对象到数据库 在保存多的对象到数据库 这样是最优化不会多出update语句
/**
* 映射多对一的关联关系（外键）保存
* */
public static void testForeignKey() {
StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();// 配置文件configure()
SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Customer customer=new Customer();
customer.setCustomerName("张三");
Order order1=new Order();
order1.setOrderName("自行车");
order1.setCustomer(customer);
Order order2=new Order();
order2.setOrderName("帐篷");
order2.setCustomer(customer);
session.save(customer);
session.save(order1);
session.save(order2);
//外键值没有先保存得到外键值的化会多出update语句
transaction.commit();
session.close();
sessionFactory.close();
}
查询
- 1.默认不会查询外键的关联对象
- 2.在要使用外键关联的对象时才会查询（懒加载）
- 3.会发生懒加载移除
- 4.默认情况下外键指向的对象是一个代理对象
/**
* 映射多对一的关联关系（外键）查询
*
* 1.默认不会查询外键的关联对象
* 2.在要使用外键关联的对象时才会查询（懒加载）
* 3.会发生懒加载移除
* 4.默认情况下外键指向的对象是一个代理对象
* */
public static void testForeignKeyGet() {
StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();// 配置文件configure()
SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Order order = session.get(Order.class, 1);
Customer customer = order.getCustomer();
System.out.println(customer);
transaction.commit();
session.close();
sessionFactory.close();
}
更新 和正常使用一样
/**
* 映射多对一的关联关系（外键）更新
* */
public static void testForeignKeyUpdate() {
StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();// 配置文件configure()
SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Order order = session.get(Order.class, 1);
order.getCustomer().setCustomerName("王五");
transaction.commit();
session.close();
sessionFactory.close();
}
删除
- 1 如果没有设置级联，没有被其他表数据外键所应用才可以删除
/**
* 映射多对一的关联关系（外键）删除
* 1 如果没有设置级联，没有被其他表数据外键所应用才可以删除
* */
public static void testForeignKeyDelete() {
StandardServiceRegistry registry = new StandardServiceRegistryBuilder().configure().build();// 配置文件configure()
SessionFactory sessionFactory = new MetadataSources(registry).buildMetadata().buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Customer customer = session.get(Customer.class, 1);
session.delete(customer);
transaction.commit();
session.close();
sessionFactory.close();
}
