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">