JPA关系映射之one-to-one

一对一关联有两种实现方式：一种是共享的主键关联，另一种是一对一的外键关联

1、共享的主键关联：让两个对象具有共同的主键值，以表明他们之间的一一对应关系。

Person.java类

 public class Person implements java.io.Serializable {

     // Fields

     private Integer id;
     private String name;
     private Idcard idcard;

     // Constructors

     /** default constructor */
     public Person() {
     }

     /** full constructor */
     public Person(String name) {
         this.name = name;
     }

     // Property accessors

     public Integer getId() {
         return this.id;
     }

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

     public String getName() {
         return this.name;
     }

     public void setName(String name) {
         this.name = name;
     }
     public Idcard getIdcard() {
         return idcard;
     }

     public void setIdcard(Idcard idcard) {
         this.idcard = idcard;
     }
 }

Idcard.java类

 public class Idcard implements java.io.Serializable {

     // Fields

     private Integer id;
     private String idcardno;
     private Person person;

     // Constructors

     /** default constructor */
     public Idcard() {
     }

     /** full constructor */
     public Idcard(String idcardno) {
         this.idcardno = idcardno;
     }

     // Property accessors

     public Integer getId() {
         return this.id;
     }

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

     public String getIdcardno() {
         return this.idcardno;
     }

     public void setIdcardno(String idcardno) {
         this.idcardno = idcardno;
     }

     public Person getPerson() {
         return person;
     }

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

 }

Person.hbm.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 <!--
     Mapping file autogenerated by MyEclipse Persistence Tools
 -->
 <hibernate-mapping>
     <class name="com.db.entity.Person" table="person" catalog="mydb">
         <id name="id" type="java.lang.Integer">
             <column name="id" />
             <generator class="native" />
         </id>
         <property name="name" type="java.lang.String">
             <column name="name" length="30" />
         </property>
         <one-to-one name="idcard" class="com.db.entity.Idcard" cascade="all" />
     </class>
 </hibernate-mapping>

Idcard.hbm.xml

 <hibernate-mapping>
     <class name="com.db.entity.Idcard" table="idcard" catalog="mydb">
         <id name="id" type="java.lang.Integer">
             <column name="id" />
             <generator class="foreign">
             <param name="property">person</param>
             </generator>
         </id>
         <one-to-one name="person" constrained="true" class="com.db.entity.Person"></one-to-one>
         <property name="idcardno" type="java.lang.String">
             <column name="idcardno" length="20" />
         </property>
     </class>
 </hibernate-mapping>

bibernate.cfg.xml

 <?xml version='1.0' encoding='UTF-8'?>
 <!DOCTYPE hibernate-configuration PUBLIC
           "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
           "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 <!-- Generated by MyEclipse Hibernate Tools.                   -->
 <hibernate-configuration>

     <session-factory>
         <property name="dialect">
             org.hibernate.dialect.MySQLDialect
         </property>
         <property name="connection.url">
             jdbc:mysql://localhost:3306/mydb
         </property>
         <property name="connection.username">root</property>
         <property name="connection.password">123456</property>
         <property name="connection.driver_class">
             com.mysql.jdbc.Driver
         </property>
         <property name="myeclipse.connection.profile">
             MyDBAccount
         </property>
         <mapping resource="com/db/entity/Idcard.hbm.xml" />
         <mapping resource="com/db/entity/Person.hbm.xml" />
     </session-factory>

 </hibernate-configuration>

测试代码：

 public class TestOneOne {

     public static void main(String[] args) {
         // TODO Auto-generated method stub

         Session session=null;
         session=HibernateSessionFactory.getSession();
         session.beginTransaction();
         Idcard idcard=new Idcard();
         idcard.setIdcardno("2345678901");
         Person person=new Person();
         person.setName("Lily");
         person.setIdcard(idcard);
         idcard.setPerson(person);
         session.save(person);
         session.save(idcard);
         session.getTransaction().commit();

     }

 }

2、一对一的外键关联：外键关联，本来是用于多对一的配置，但是加上唯一的限制之后（采用<many-to-one>标签来映射，指定多的一端unique为true，这样就限制了多的一端的多重性为一），也可以用来表示一对一关联关系，其实它就是多对一的特殊情况。

首先在表idcard中新添加一列pid用于共享数据

Person.java类

 public class Person implements java.io.Serializable {

     // Fields

     private Integer pid;
     private String name;
     private Idcard idcard;

     // Constructors

     /** default constructor */
     public Person() {
     }

     /** full constructor */
     public Person(String name) {
         this.name = name;
     }

     // Property accessors

     public Integer getPid() {
         return this.pid;
     }

     public void setPid(Integer pid) {
         this.pid = pid;
     }

     public String getName() {
         return this.name;
     }

     public void setName(String name) {
         this.name = name;
     }
     public Idcard getIdcard() {
         return idcard;
     }

     public void setIdcard(Idcard idcard) {
         this.idcard = idcard;
     }
 }

idcard.java类

 public class Idcard implements java.io.Serializable {

     // Fields

     private Integer iid;
     private String idcardno;
     private Person person;

     // Constructors

     /** default constructor */
     public Idcard() {
     }

     /** full constructor */
     public Idcard(String idcardno) {
         this.idcardno = idcardno;
     }

     // Property accessors

     public Integer getIid() {
         return this.iid;
     }

     public void setIid(Integer iid) {
         this.iid = iid;
     }

     public String getIdcardno() {
         return this.idcardno;
     }

     public void setIdcardno(String idcardno) {
         this.idcardno = idcardno;
     }

     public Person getPerson() {
         return person;
     }

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

 }

Person.hbm.xml

 <hibernate-mapping>
     <class name="com.db.entity.Person" table="person" catalog="mydb">
         <id name="pid" type="java.lang.Integer">
             <column name="pid" />
             <generator class="native" />
         </id>
         <property name="name" type="java.lang.String">
             <column name="name" length="30" />
         </property>
         <one-to-one name="idcard" class="com.db.entity.Idcard" property-ref="person"></one-to-one>
     </class>
 </hibernate-mapping>

Idcard.hbm.xml

 <hibernate-mapping>
     <class name="com.db.entity.Idcard" table="idcard" catalog="mydb">
         <id name="iid" type="java.lang.Integer">
             <generator class="native">
             </generator>
         </id>
         <many-to-one name="person" column="pid" class="com.db.entity.Person"
             cascade="save-update" unique="true"></many-to-one>
         <property name="idcardno" type="java.lang.String">
             <column name="idcardno" length="20" />
         </property>
     </class>
 </hibernate-mapping>

bibernate.cfg.xml文件和测试代码同上。

如果使用注解映射外键，则注解如下：

Idcard.java类

 public class Idcard implements java.io.Serializable {

     // Fields
     private Person person;

     @OneToOne
     @JoinColumn(name="pid")
     public Person getPerson() {
         return person;
     }

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

 }

Person.java类

 public class Person implements java.io.Serializable {

     // Fields
     private Idcard idcard;

     @OneToOne(mappedBy="person")
     public Idcard getIdcard() {
         return idcard;
     }

     public void setIdcard(Idcard idcard) {
         this.idcard = idcard;
     }
 }