Hibernate关系映射（一） 基于外键的单向一对一

模拟用户和地址的映射关系，一个用户只有一个地址，用户知道地址，但是地址不知道用户。用户对地址的单向一对一映射。

一、建立实体类

Account.cs类

package com.lxit.entity;

import java.io.Serializable;

public class Account implements Serializable{
    public Account(){

    }
    private int id;
    private String name;
    private String password;
    //需要添加被控端的引用
    private Address address;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = 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.cs类  地址类

package com.lxit.entity;

import java.io.Serializable;

public class Address implements Serializable{
    public Address(){

    }
    private int id;
    private String name;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

}

二、映射文件

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="com.lxit.entity.Account" table="Account">
  <id column="id" name="id">
   <generator class="native"/>
  </id>
  <property column="name" generated="never" lazy="false" name="name"/>
  <property column="password" generated="never" lazy="false" name="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 -->
  <many-to-one column="address_id" name="address" 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="com.lxit.entity.Address" table="Address">
  <id column="id" name="id">
   <generator class="native"/>
  </id>
  <property column="name" generated="never" lazy="false" name="name"/>
 </class>
</hibernate-mapping>

三、HibernateUtil工具类

package com.lxit.util;

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

/**
 * Hibernate3.3工具类
 * @author Administrator
 *
 */
public class HibernateUtil {
    private static SessionFactory factory;

    static{
        Configuration cfg = new Configuration().configure();
        factory = cfg.buildSessionFactory();
    }

    public static SessionFactory getFactory(){
        return factory;
    }

    public static Session getSession(){
        return factory.openSession();
    }

    public static void CloseSession(Session session){
        if(session != null){
            session.close();
        }
    }
}

四、hibernate.cfg.xml配置文件

<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory name="foo">
    <!-- 配置数据库连接 -->
    <property name="hibernate.dialect">
        org.hibernate.dialect.MySQL5Dialect
    </property>
    <property name="hibernate.connection.driver_class">
        com.mysql.jdbc.Driver
    </property>
    <property name="hibernate.connection.url">
        jdbc:mysql://127.0.0.1:3306/test
    </property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">root</property>

    <property name="show_sql">true</property>
    <property name="format_sql">true</property>

    <property name="hbm2ddl.auto">update</property>
    <mapping resource="com/lxit/entity/Account.hbm.xml" />
    <mapping resource="com/lxit/entity/Address.hbm.xml" />

</session-factory>
</hibernate-configuration>

五、Jutil测试类

package com.lxit.demo2.test;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.lxit.entity.Account;
import com.lxit.entity.Address;
import com.lxit.util.HibernateUtil;

public class AccountTest {

    @Test
    public void Add(){
        Transaction tx = null;
        Session session = HibernateUtil.getSession();
        tx = session.beginTransaction();

        Address address= new Address();
        address.setName("深圳宝安");
        session.save(address);

        Account account = new Account();
        account.setName("zhangsan");
        account.setPassword("123");
        account.setAddress(address);

        try {
            session.save(account);
            tx.commit();
        } catch (Exception e) {
            e.printStackTrace();
            tx.rollback();
        }finally{
            HibernateUtil.CloseSession(session);
        }
    }

    @Test
    public void Add2(){
        Transaction tx = null;
        Session session = HibernateUtil.getSession();
        tx = session.beginTransaction();

        Address address= new Address();
        address.setName("深圳福田");
        session.save(address);

        Account account1 = new Account();
        account1.setName("lisi");
        account1.setPassword("123");
        account1.setAddress(address);

        Account account2 = new Account();
        account2.setName("wangwu");
        account2.setPassword("123");
        account2.setAddress(address);

        try {
            //重复添加第二个用户，地址相同，则会报错
            session.save(account1);
            session.save(account2);
            tx.commit();
        } catch (Exception e) {
            e.printStackTrace();
            tx.rollback();
        }finally{
            HibernateUtil.CloseSession(session);
        }
    }
}

总结：单向一对一必须通过实体类生成数据库表的方式，会自动生成相关的约束，直接创建表无效。