Hibernate 关联映射之一对一

Hibernate的关联映射包括：

一对一（Persion - IDCard）

一对多（Department - Employee）

多对一（Employee - Department）

多对多（Teacher - Student）

组件映射（User - Name）

集合映射（Set、List、Map）

inverse和cascade（Employee - Department）

本文以一对一为例：

一个人对应一个身份证（Persion- IdCard）

(1) 基于主键的one-to-one（Persion的配置文件）

从对象IdCard使用了和主对象Person相同的主键，IdCard的主键在此即充当了主键又充当的外键。

<id name="id">

    <generator  class="foreign"/>

        <param  name="property">idCard</param>

    </generator>

</id>

<one-to-one  name="idCard"  constrained="true"> 

实体类：Persion.java 和 IdCard.java

package com.cos.entity;

public class Person {
	private int id;
	private String name;
	private IdCard idCard;//一对一
	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 IdCard getIdCard() {
		return idCard;
	}
	public void setIdCard(IdCard idCard) {
		this.idCard = idCard;
	}
}

package com.cos.entity;

public class IdCard {
	private int id;
	private String idNo;
	private Person person;//一对一
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getIdNo() {
		return idNo;
	}
	public void setIdNo(String idNo) {
		this.idNo = idNo;
	}
	public Person getPerson() {
		return person;
	}
	public void setPerson(Person person) {
		this.person = person;
	}
}

 映射文件：Person.hbm.xml 和 IdCard.hbm.xml

<?xml version="1.0"?>
<!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.cos.entity.Person" lazy="true">
		<id name="id">
			<generator class="native"/>
		</id>	
		<property name="name"/>
		<one-to-one name="idCard"/>
	</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!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.cos.entity.IdCard" table="id_card" lazy="true">
		<!-- 此id既是主键又是外键 -->
		<id name="id">
			<generator class="foreign">
				<!-- 此外键的值根据one-to-one中的person获得 -->
				<param name="property">person</param>
			</generator>
		</id>	
		<property name="idNo"/>
		<!-- constrained="true"表示是受约束的 -->
		<one-to-one name="person" constrained="true"/>
	</class>
</hibernate-mapping> 

Hibernate配置文件：hibernate.cfg.xml

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

<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql:///hi</property>
        <property name="hibernate.connection.username"></property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.hbm2ddl.auto">create</property>
        <property name="show_sql">true</property>
		<mapping resource="com/cos/entity/Person.hbm.xml"/>
		<mapping resource="com/cos/entity/IdCard.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

工具类：HibernateUtil.java

package com.cos.util;

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

public final class HibernateUtil {

	private static SessionFactory sesseionFactory;

	static {
		Configuration conf = new Configuration();
		conf.configure();
		sesseionFactory = conf.buildSessionFactory();
	}

	public static SessionFactory getSesseionFactory() {
		return sesseionFactory;
	}
} 

测试类：One2One.java

package com.cos.main;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import com.cos.entity.IdCard;
import com.cos.entity.Person;
import com.cos.util.HibernateUtil;

public class One2One {

	public static void main(String[] args) {
		add();
	}
	public static void add(){
		SessionFactory  sessionFactory = null;
		Session s = null;
		Transaction t = null;
		try{
			sessionFactory = HibernateUtil.getSesseionFactory();
			s = sessionFactory.openSession();
			t = s.beginTransaction();
			Person person = new Person();
			person.setName("person 1");
			IdCard idCard = new IdCard();
			idCard.setIdNo("450846222002212131");
			idCard.setPerson(person);
			s.save(person);
			s.save(idCard);
			t.commit();
			s.close();
			sessionFactory.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

 测试类（查询）：One2One.java

package com.cos.main;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import com.cos.entity.IdCard;
import com.cos.entity.Person;
import com.cos.util.HibernateUtil;

public class One2One {

	public static void main(String[] args) {
		query(1);//Person为主对象
		query1(1);//IdCard为从对象
	}
	//查询主对象
	public static void query(int id){
		SessionFactory  sessionFactory = null;
		Session s = null;
		try{
			sessionFactory = HibernateUtil.getSesseionFactory();
			s = sessionFactory.openSession();
			Person person = (Person)s.get(Person.class, id);
			System.out.println(person.getIdCard().getIdNo());
			s.close();
			sessionFactory.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
	//查询从对象
	public static void query1(int idCard){
		SessionFactory  sessionFactory = null;
		Session s = null;
		try{
			sessionFactory = HibernateUtil.getSesseionFactory();
			s = sessionFactory.openSession();
			IdCard idc = (IdCard)s.get(IdCard.class,idCard);
			System.out.println(idc.getPerson().getName());
			s.close();
			sessionFactory.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

表结构：person表 和id_card表

CREATE TABLE `person` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

CREATE TABLE `id_card` (
  `id` int(11) NOT NULL,
  `idNo` varchar(255) default NULL,
  PRIMARY KEY  (`id`),
  KEY `FK627C1FB48F4EE9A7` (`id`),
  CONSTRAINT `FK627C1FB48F4EE9A7` FOREIGN KEY (`id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

(2) 基于外键的one-to-one  可以描述为多对一，加unique="true"约束

从对象IdCard和主对象Person使用了各自的主键

Persion.hbm.xml的配置文件：

<one-to-one  name="idCard" property-ref="person"/>

IdCard.hbm.xml的配置文件：

<many-to-one  name="person"  column="person_id"  unique="true"  not-null="true"/>

<?xml version="1.0"?>
<!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.cos.entity.Person" lazy="true">
		<id name="id">
			<generator class="native"/>
		</id>	
		<property name="name"/>
		<one-to-one name="idCard" property-ref="person"/>
	</class>
</hibernate-mapping>

<?xml version="1.0"?>
<!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.cos.entity.IdCard" table="id_card" lazy="true">
		<id name="id">
			<generator class="native"/>
		</id>	
		<property name="idNo"/>
		<many-to-one name="person" column="person_id" unique="true"/>
	</class>
</hibernate-mapping>

 表结构：

CREATE TABLE `person` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

CREATE TABLE `id_card` (
  `id` int(11) NOT NULL auto_increment,
  `idNo` varchar(255) default NULL,
  `person_id` int(11) default NULL,
  PRIMARY KEY  (`id`),
  UNIQUE KEY `person_id` (`person_id`),
  KEY `FK627C1FB4C22976D1` (`person_id`),
  CONSTRAINT `FK627C1FB4C22976D1` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1