Hibernate学习(二)关系映射----基于外键的单向一对一

事实上，单向1-1与N-1的实质是相同的，1-1是N-1的特例，单向1-1与N-1的映射配置也非常相似。只需要将原来的many-to-one元素增加unique="true"属性，用于表示N的一端也必须是唯一的，在N的一端增加了唯一的约束，即成为单向1-1。基于外键的单向1-1的配置将与无连接表N-1关联的many-to-one增加unique="true"属性即可。

一、模型介绍

一个人（account）对应一个地址（address）。

二、实体

account类

package entity;

import java.io.Serializable;
public class account implements Serializable{
        public account(){
            
        }
        // 建议hibernate中不用使用id,name这种关键字 可能会报错
        private int account_id;
        private String account_name;
        private String password;
        //需要添加被控端的引用 此处添加的是对应关系 即一个人对应一个地址的地址对象 
        private address address;
        
        public int getAccount_id() {
            return account_id;
        }
        public void setAccount_id(int account_id) {
            this.account_id = account_id;
        }
        public String getAccount_name() {
            return account_name;
        }
        public void setAccount_name(String account_name) {
            this.account_name = account_name;
        }
        public String getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        public address getAddress() {
            return address;
        }
        public void setAddress(address address) {
            this.address = address;
        }    
}

address实体类

package entity;

import java.io.Serializable;

public class address implements Serializable{
        public address(){    
        }
        private int address_id;
        private String address_name;
        
        public int getAddress_id() {
            return address_id;
        }
        public void setAddress_id(int address_id) {
            this.address_id = address_id;
        }
        public String getAddress_name() {
            return address_name;
        }
        public void setAddress_name(String address_name) {
            this.address_name = address_name;
        }        
}

映射关系配置
account.hbm.xml

<?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 = "entity.account" table ="account">
    <id  column = "account_id" name = "account_id">
      <generator class="native"/>  <!--主键生成方式  所以在创建表的时候要主键自增
-->    </id>
    <property name="account_name" type = "java.lang.String" column = "account_name"/>
    <property name="password" type="java.lang.String" column = "password"/>
     <!-- 通过many-to-one 标签添加唯一属性约束，建立一对一关联关系 
     此处映射的意思是 account的adress属性对应着外表的address_id列 且填加了唯一约束  说明address_id是唯一的     
     
-->
    <many-to-one name="address" column="address_id" unique="true"/>
    <!-- 必须通过映射关系生成的表才会生成唯一约束，否则不会生成 -->
  </class>
</hibernate-mapping>

address.hbm.xml

<?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 = "entity.address" table = "address">
      <id name="address_id" column="address_id">
      <generator class="native"/>
      </id>
      <!-- generated= never  标明此属性值不是从数据库中生成。generated默认值是never。
           generated= insert  标明此属性值在insert的时候生成，但是不会在随后的update时重新生成。
           generated= always  标明此属性值在insert和update时都会被生成
       -->
      <property name="address_name" type = "java.lang.String" column = "address_name" generated="never" lazy="false"/>
     </class>
</hibernate-mapping>

这里讲通用逻辑封装成了一个方法了

/**
 * @author Administrator
 *
 */
package HibernateUtil;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtil {
    private static SessionFactory factory;
    static{
        Configuration cnn = new Configuration().configure();
        factory = cnn.buildSessionFactory();
    }
    public static SessionFactory getSessionFactory(){
        return factory;
    }
    public static Session getOneSession(){
        return factory.openSession();
    }
    public static void ClossSession(Session session){
        if(session != null){
            session.close();
        }
    }
}

建表就不说了但是注意不要忘记创建自增和索引名字必须是Hibernate.sequence .
hibernate.hbm.xml同Hibernate学习一中的配置只是添加了映射文件 <mapping resource="account.hbm.xml"/><mapping resource="address.hbm.xml"/>

测试

package text;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import entity.account;
import entity.address;

import HibernateUtil.HibernateUtil;

public class textManytoOne {
    
   @Test
   public void add(){
       Transaction tx = null;
       Session session = HibernateUtil.getOneSession();
       tx=session.beginTransaction();
       
      address address = new address();
       address.setAddress_name("天津");
       session.save(address);
      
       account account = new account();
       account.setAccount_name("大伟哥666");
       account.setPassword("123456");
       account.setAddress(address);
       
       // 重复添加

       account account1 = new account();
       account1.setAccount_name("小老虎666");
       account1.setPassword("123456");
       account1.setAddress(address);
      
      try{
      session.save(account);
      session.save(account1);
      tx.commit();
      }catch(HibernateException e){
          e.printStackTrace();
          tx.rollback();
      }finally{
          HibernateUtil.ClossSession(session);
      }
   }
}

总结注意
1.在多表实体类中记得添加被控端的对象的引用 且属性名字最好不用和关键字冲突

2.要在多表的映射文件中写上<many-to-one name="被控端引用对象" column="外键 也就是另一张表的主键" unique="是否对外键加唯一">

3.创建表的时候主键索引名字是Hibernate.sequence 不知道为什么  但是我的名字不是这个就报错

4.Hibernate的配置文件中记得添加实体类的映射文件 <mapping resource="xxx.hbm.xml">