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;
}
}