上篇写了一对一,那么在这篇我们讲一对多,那么在表中的一对多,是使用外键关联,通过一张表的一个键另一个表的外键来建立一多关系;
而在类中表示为一个类中有一个集合属性包含对方类的很多对象,而在另一个类中,只包含前术类的一个对象,从而实现一对多关系的建立!
而在Hibernate中采用的是Set类型集合,而使用<one-to-many>主<many-to-one>来实现,好了,我们来看一下:
首先看看表结构!
customer表:
create
table
customers
(
ID bigint not null primary key auto_increment,
userName varchar ( 20 )
);
(
ID bigint not null primary key auto_increment,
userName varchar ( 20 )
);
Order表:
create
table
orders
(
ID bigint not null primary key auto_increment,
customers_ID bigint , -- 应该为customers(ID)外键
orderDescription varchar ( 50 ) -- 订单描述
);
(
ID bigint not null primary key auto_increment,
customers_ID bigint , -- 应该为customers(ID)外键
orderDescription varchar ( 50 ) -- 订单描述
);
有了上面简单的客户表与订单表,来建立一个Project!~并且添加Hibernate~并由上面二张表生成Beans,主键都是native类型~自动递增!
我们将 自动生成的Customer.java Bean添加一个SET属性,代码如下:
package fengyan.Hibernate;
import java.util.HashSet;
import java.util.Set;
/**
*Authod: fengyan
* date: 2006-12-30 01:02
*/
public class Customers implements java.io.Serializable {
// Fields
private Long id;
private String userName;
// 必须定义一个Set集合类型的属性以及它的get和set方法,
// 它持有一个Customers对象所发出的所有订单的引用
private Set orders = new HashSet();
// Constructors
public Set getOrders() {
return orders;
}
public void setOrders(Set orders) {
this .orders = orders;
}
/** default constructor */
public Customers() {
}
/** full constructor */
public Customers(String userName) {
this .userName = userName;
}
// Property accessors
public Long getId() {
return this .id;
}
public void setId(Long id) {
this .id = id;
}
public String getUserName() {
return this .userName;
}
public void setUserName(String userName) {
this .userName = userName;
}
}
为Order.java Bean 去掉cid(CustomerID)并添加一个Customer属性,代码如下:
package fengyan.Hibernate;
/**
*Authod: fengyan
* date: 2006-12-30 01:02
*/
public class Orders implements java.io.Serializable {
// Fields
private Long id;
// private Long customersId;
private String orderDescription;
// 添加一个Customers属性,用来引用一个订单对象所属的客户对象
private Customers customer;
// Constructors
public Customers getCustomer() {
return customer;
}
public void setCustomer(Customers customer) {
this .customer = customer;
}
/** default constructor */
public Orders() {
}
public Orders(String description)
{
this .orderDescription = description;
}
// Property accessors
public Long getId() {
return this .id;
}
public void setId(Long id) {
this .id = id;
}
public String getOrderDescription() {
return this .orderDescription;
}
public void setOrderDescription(String orderDescription) {
this .orderDescription = orderDescription;
}
}
修改Customer.hbm.xml映射文件:
<?
xml version="1.0" encoding="GBK"
?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="fengyan.Hibernate.Customers" table ="customers" catalog ="study" >
< id name ="id" type ="java.lang.Long" >
< column name ="ID" />
< generator class ="native" />
</ id >
< property name ="userName" type ="java.lang.String" >
< column name ="userName" length ="20" />
</ property >
<!-- name集合属性orders
table对应的表名
cascade 级联关系,当保存或更新时会级联保存与这个Customers对象相关联的所有Orders对象
inverse=true是将 控权抛出(给Orders) -->
< set name ="orders" table ="orders" cascade ="save-update" inverse ="true" >
< key column ="customers_ID" ></ key > <!-- 表字段 -->
< one-to-many class ="fengyan.Hibernate.Orders" /> <!-- 关联的类 -->
</ set >
</ class >
</ hibernate-mapping >
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="fengyan.Hibernate.Customers" table ="customers" catalog ="study" >
< id name ="id" type ="java.lang.Long" >
< column name ="ID" />
< generator class ="native" />
</ id >
< property name ="userName" type ="java.lang.String" >
< column name ="userName" length ="20" />
</ property >
<!-- name集合属性orders
table对应的表名
cascade 级联关系,当保存或更新时会级联保存与这个Customers对象相关联的所有Orders对象
inverse=true是将 控权抛出(给Orders) -->
< set name ="orders" table ="orders" cascade ="save-update" inverse ="true" >
< key column ="customers_ID" ></ key > <!-- 表字段 -->
< one-to-many class ="fengyan.Hibernate.Orders" /> <!-- 关联的类 -->
</ set >
</ class >
</ hibernate-mapping >
修改Order.hbm.xml,内容如下:
<?
xml version="1.0" encoding="utf-8"
?>
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="fengyan.Hibernate.Orders" table ="orders" catalog ="study" >
< id name ="id" type ="java.lang.Long" >
< column name ="ID" />
< generator class ="native" />
</ id >
< property name ="orderDescription" type ="java.lang.String" >
< column name ="orderDescription" length ="50" />
</ property >
<!-- name属性名
class对应的类
column对应的表字段 -->
< many-to-one name ="customer" class ="fengyan.Hibernate.Customers" column ="customers_ID" ></ many-to-one >
</ class >
</ hibernate-mapping >
<! DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="fengyan.Hibernate.Orders" table ="orders" catalog ="study" >
< id name ="id" type ="java.lang.Long" >
< column name ="ID" />
< generator class ="native" />
</ id >
< property name ="orderDescription" type ="java.lang.String" >
< column name ="orderDescription" length ="50" />
</ property >
<!-- name属性名
class对应的类
column对应的表字段 -->
< many-to-one name ="customer" class ="fengyan.Hibernate.Customers" column ="customers_ID" ></ many-to-one >
</ class >
</ hibernate-mapping >
然后我们建立一个CustomersDAO操作类
package
fengyan.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
public class CustomersDAO {
public void save(Customers customer)
{
Session session = HibernateSessionFactory.getSession(); // 会话
try
{
Transaction tx = session.beginTransaction(); // 事物
session.save(customer); // 保存
tx.commit(); // 提交事物
}
catch (Exception e)
{
System.out.println( " DAO has Errors: " + e);
}
finally
{
session.close(); // 关闭会话
}
}
}
import org.hibernate.Session;
import org.hibernate.Transaction;
public class CustomersDAO {
public void save(Customers customer)
{
Session session = HibernateSessionFactory.getSession(); // 会话
try
{
Transaction tx = session.beginTransaction(); // 事物
session.save(customer); // 保存
tx.commit(); // 提交事物
}
catch (Exception e)
{
System.out.println( " DAO has Errors: " + e);
}
finally
{
session.close(); // 关闭会话
}
}
}
再来建立一个Servlet MyServlet.java代码如下:
package
fengyan.Hibernate;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MyServlet c
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MyServlet c
评论