Hibernate关联关系映射---1对1

1对1
Hibernate的1对1关联关系映射有两种
1 主表主键与从表主键，形成主外键关系(从表的主键又是外键)
2 主表主键与从表外键(必须唯一unique)，形成主外键关系

1对1中PO使用的一个，只是hbm.xml映射存在两次写法

1对1分析：

实例：公司Company ： 地址Address

jvava bean

Address.java:

package com.my.bean;public class Address {    private Integer id;    private String addr;    //第一个地址 属于一个公司    private Company company;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getAddr() {        return addr;    }    public void setAddr(String addr) {        this.addr = addr;    }    public Company getCompany() {        return company;    }    public void setCompany(Company company) {        this.company = company;    }}

Company.java:

package com.my.bean;public class Company {    private Integer id;    private String name;    //第一个公司只有一个地址    private Address address;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Address getAddress() {        return address;    }    public void setAddress(Address address) {        this.address = address;    }}

主表主键与从表主键，形成主外键关系(从表的主键又是外键)

Address.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"><hibernate-mapping>    <class name="com.my.bean.Address" table="t_address_pk">        <id name="id">            <!-- 从表主键 又是主表的外键 -->            <generator class="foreign">                <param name="property">company</param>            </generator>        </id>        <property name="addr"></property>        <!-- 1对1 ,此项确定提供给约束使用的 -->        <one-to-one name="company" class="com.my.bean.Company" constrained="true"></one-to-one>    </class></hibernate-mapping>

Company.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"><hibernate-mapping>    <class name="com.my.bean.Company" table="t_company_pk">        <id name="id">            <generator class="native"></generator>        </id>        <property name="name"></property>        <!-- 1对1 -->        <one-to-one name="address" class="com.my.bean.Address"></one-to-one>    </class></hibernate-mapping>

主表主键与从表外键(必须唯一unique)，形成主外键关系

Address.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"><hibernate-mapping>    <class name="com.my.bean.Address" table="t_address">        <id name="id">            <generator class="native"></generator>        </id>        <property name="addr"></property>        <!-- 特例：本身多对1，但此时要是地址i必须唯一 ， column指定就是外键的名称-->        <many-to-one name="company" class="com.my.bean.Company" column="company_id" unique="true"></many-to-one>    </class></hibernate-mapping>

Company.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"><hibernate-mapping>    <class name="com.my.bean.Company" table="t_company">        <id name="id">            <generator class="native"></generator>        </id>        <property name="name"></property>        <!-- foreign-key 直接指定外键的值，property-ref通过属性获得对应的表中外键名称 -->        <one-to-one name="address" class="com.my.bean.Address"  foreign-key="company_id"></one-to-one>    </class></hibernate-mapping>

测试类：

package com.my.bean;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import org.junit.Test;public class TestOneToOne {    private SessionFactory sessionFactory = new Configuration()                                .configure()                                .addClass(Company.class)                                .addClass(Address.class)                                .buildSessionFactory();    @Test    public void demo01(){        Session session = sessionFactory.openSession();        session.close();    }}