Hibernate一对一

 一对一主键关联不需要额外的表字段；如果两行是通过这种一对一关系相关联的，那么这两行就共享同样的主关键字值。所以如果你希望两个对象通过主键一对一关联，你必须确认它们被赋予同样的标识值！

 

比如说，对下面的Employee和Person进行主键一对一关联:

<one-to-one name="person" class="Person"/>

 

<one-to-one name="employee" class="Employee" constrained="true"/>

 

现在我们必须确保PERSON和EMPLOYEE中相关的字段是相等的。我们使用一个被成为foreign的特殊的hibernate标识符生成策略：

<class name="person" table="PERSON">
    <id name="id" column="PERSON_ID">
        <generator class="foreign">
            <param name="property">employee</param>
        </generator>
    </id>
    ...
    <one-to-one name="employee"
        class="Employee"
        constrained="true"/>
</class>

 

一个刚刚保存的Person实例被赋予和该Person的employee属性所指向的Employee实例同样的关键字值。

 

下面是居民与身份证的例子：

居民Person类

package org.hibernate.domain;

public class Person {
	private int id;
	private String name;
	private IdCard idCard;

	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;
	}

}

 

身份证IdCard类：

package org.hibernate.domain;


public class IdCard {
	private int id;
	private Person person;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public Person getPerson() {
		return person;
	}

	public void setPerson(Person person) {
		this.person = person;
	}

}

 

映射文件：

<?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 package="org.hibernate.domain">
	<class name="Person" table="person">
		<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 package="org.hibernate.domain">
	<class name="IdCard" table="idCard">
		<id name="id">
			<generator class="foreign">
				<param name="property">person</param>
			</generator>
		</id>

		<one-to-one name="person" constrained="true" />
	</class>
</hibernate-mapping>

 

测试类：

package org.hibernate.test;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.domain.IdCard;
import org.hibernate.domain.Person;
import org.hibernate.util.HibernateUtil;

public class OneToOne {
	public static void main(String[] args) {
		Person person = add();
		
		person = queryPerson(person.getId());
		
		queryIdCard(person.getIdCard().getId());
	}

	public static Person add() {
		Session session = null;
		Transaction tx = null;

		try {
			session = HibernateUtil.getSession();

			IdCard idCard = new IdCard();

			Person person = new Person();
			person.setName("new person");
			person.setIdCard(idCard);

			idCard.setPerson(person);

			tx = session.beginTransaction();
			session.save(person);
			session.save(idCard);
			tx.commit();

			return person;
		} finally {
			if (session != null)
				session.close();
		}
	}

	public static Person queryPerson(int id) {
		Session session = null;
		Transaction tx = null;

		try {
			session = HibernateUtil.getSession();
			tx = session.beginTransaction();
			Person person = (Person) session.get(Person.class, id);
			tx.commit();
			
			return person;
		} finally {
			if (session != null)
				session.close();
		}
	}
	
	public static IdCard queryIdCard(int id) {
		Session session = null;
		Transaction tx = null;

		try {
			session = HibernateUtil.getSession();
			tx = session.beginTransaction();
			IdCard idCard = (IdCard) session.get(IdCard.class, id);
			tx.commit();
			return idCard;
		} finally {
			if (session != null)
				session.close();
		}
	}
}

 

控制台打印结果：

 
 

 另一种方式是一个外键和一个惟一关键字对应，上面的Employee和Person的例子，如果使用这种关联方式，可以表达成：

<many-to-one name="person" class="Person" column="PERSON_ID" unique="true"/>

 如果在Person的映射加入下面几句，这种关联就是双向的：

<one-to-one name"employee" class="Employee" property-ref="person"/>

 对于居民与身份证的例子，则配置文件需修改为，如下：

<?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 package="org.hibernate.domain">
	<class name="Person" table="person">
		<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 package="org.hibernate.domain">
	<class name="IdCard" table="idCard">
		<id name="id">
			<generator class="native" />
		</id>

		<many-to-one name="person" column="person_id" unique="true" />
	</class>
</hibernate-mapping>