Hibernate关联映射之_一对一

数据库模型

　　一般对一对一的关系而言，会存在一个主从关系。如 人 与 身份证，就是一个一对一关系， 人 是主，身份证 是从

Person

　　PK：id

　　　　name

　　　　age

Id_Card

　　PK、FK：id

　　　　useful_life

一般在设计的时候，对于主表的id，由自增长或序列产生，从表的主键id可以直接使用主表的主键id，不需要自己重新生成

---

 Domain

package org.zln.hibernate.domain;

/**
 * Created by coolkid on 2015/6/20 0020.
 */
public class Person {
    private int id;
    private String name;
    private IdCard idCard;
...43 }

package org.zln.hibernate.domain;


/**
 * Created by coolkid on 2015/6/20 0020.
 */
public class IdCard {
    private int id;
    private String usefulLife;//证件有效期
    private Person person;
...
}

XML

 Person.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 package="org.zln.hibernate.domain">

    <class name="Person" table="person">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="name" column="name"/>
        <!--一对一关系映射-->
        <one-to-one name="idCard" />
    </class>

</hibernate-mapping>

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 package="org.zln.hibernate.domain">

    <class name="IdCard" table="id_card">
        <id name="id" column="id">
            <!--主键依赖类中的属性-->
            <generator class="foreign">
                <!--外键从person属性中引用过来  从person 的 getId 方法获取-->
                <param name="property">person</param>
            </generator>
        </id>
        <property name="usefulList" column="useful_life"/>
        <!--一对一关系映射-->
        <one-to-one name="person" />
    </class>

</hibernate-mapping>

 Dao

package org.zln.hibernate.dao;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.zln.hibernate.domain.IdCard;
import org.zln.hibernate.domain.Person;
import org.zln.hibernate.utils.HibernateUtils;

/**
 * Created by coolkid on 2015/6/20 0020.
 */
public class PersonDao {

    /**
     * 保存Person及其IdCard
     * @param person 人
     * @param idCard 身份证
     */
    public void savePerson(Person person,IdCard idCard){
        Session session = null;
        Transaction transaction = null;
        try {
            session = HibernateUtils.getSession();
            transaction = session.beginTransaction();

            person.setIdCard(idCard);
            idCard.setPerson(person);

            session.save(person);
            session.save(idCard);

            transaction.commit();
        }finally {
            if (session != null){
                session.close();
            }
        }
    }

    /**
     * 通过id查询person
     * @param person person
     * @return Person
     */
    public Person getPerson(Person person){
        Session session = null;
        Person person1 = null;
        try {
            session = HibernateUtils.getSession();
            person1 = (Person) session.get(Person.class,person.getId());
        }finally {
            if (session != null){
                session.close();
            }
        }
        return person1;
    }
}

---

另一种一对一关系的实现，就是使用多对一的方法，但是对“多”加唯一性约束

在配置IdCard的name属性时，使用<many-to-one>标签，对应的column是person_id，设置unique="true"，这样也实现了一对一关系映射

<?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.zln.hibernate.domain">

    <class name="IdCard" table="id_card">
        <id name="id" column="id">
            <generator class="native"/>
        </id>
        <property name="usefulList" column="useful_life"/>
        <many-to-one name="person" column="person_id" unique="true" not-null="true"/>
    </class>

</hibernate-mapping>