双向一对一

一对一主要用在

一个一方需要的信息比较少，比如注册的登录信息

另一个一方存储的信息比较多，比如注册之后用户填写的详细信息

实现方式常用的主要有2种：

java模型都是一样，其中一个映射文件有所不同

hibernate.cfg.xml

<mapping resource="com/jege/hibernate/two/way/onetoone/User.hbm.xml" />

<mapping resource="com/jege/hibernate/two/way/onetoone/UserInfo.hbm.xml" />

User

//主一

public class User {

  private Long id;

  private String username;

  private String password;

  private UserInfo info;

UserInfo

//从一

public class UserInfo {

  private Long id;

  private Integer age;

  private String address;

  private User user;

User.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.jege.hibernate.two.way.onetoone">

    <class name="User" table="t_user">

        <id name="id">

            <generator class="native" />

        </id>

        <property name="username" />

        <property name="password" />

        <one-to-one name="info" class="UserInfo" />

    </class>

</hibernate-mapping>       

模拟外键一对一UserInfo.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.jege.hibernate.two.way.onetoone">

    <class name="UserInfo" table="t_user_info">

        <id name="id">

            <generator class="native" />

        </id>

        <property name="age" />

        <property name="address" />

        <!-- 使用多对一的方式来模拟一对一的关系 -->

        <!-- unique="true"外键的唯一 -->

        <many-to-one name="user" class="User" column="user_id" unique="true" />

    </class>

</hibernate-mapping> 

CREATE TABLE `t_user_info` (

  `id` bigint(20) NOT NULL AUTO_INCREMENT,

  `age` int(11) DEFAULT NULL,

  `address` varchar(255) DEFAULT NULL,

  `user_id` bigint(20) DEFAULT NULL,

  PRIMARY KEY (`id`),

  UNIQUE KEY `UK_ln50dwtk2w5skl1rpjfek5srv` (`user_id`),

  CONSTRAINT `FK_ln50dwtk2w5skl1rpjfek5srv` FOREIGN KEY (`user_id`) REFERENCES `t_user` (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;       

共享主键一对一

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.jege.hibernate.two.way.onetoone">

    <class name="UserInfo" table="t_user_info">

        <id name="id">

            <generator class="foreign">

                <!-- UserInfo的主键来自于当前user属性的id -->

                <param name="property">user</param>

            </generator>

        </id>

        <property name="age" />

        <property name="address" />

        <!-- 共享主键是关系双方的主键是一样的值 -->

        <!-- constrained="true"添加约束的关键 -->

        <one-to-one name="user" constrained="true" />

    </class>

</hibernate-mapping> 

CREATE TABLE `t_user_info` (

  `id` bigint(20) NOT NULL,

  `age` int(11) DEFAULT NULL,

  `address` varchar(255) DEFAULT NULL,

  PRIMARY KEY (`id`),

  CONSTRAINT `FK_ihje4vsyvt8vmuhru59ib9j1d` FOREIGN KEY (`id`) REFERENCES `t_user` (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

还有一种可以使用多一张中间表，设置主键唯一，外键同时唯一的方式，不过基本没有使用场景。

源码地址

https://github.com/je-ge/hibernate

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