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;
... }

 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>