hibernate 数据关联一对一

第一种一对一

person和card,card的id即作为主键,又作为外键

// 各村对方的一个对象

public class Person {

    private Integer id;

    private String name;

    private Card card;

}

public class Card {

    private Integer id;

    private String cardnum;

    private Person person;

}

xxx.hbm.xml 的配置

记得在总配置文件中添加这两个配置文件

<?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 package="com.kaishengit.pojo">

    <class name="Card" table="card">

        <id name="id">

        <!-- 主键生成策略变成foreign,表示又当主键又当外键 -->

            <generator class="foreign">

            <!-- 这个person是属性,指明用card这个类的person属性对应的表的主键作外键 -->

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

            </generator>

        </id>

        <property name="cardnum"/>

        <one-to-one name="person" class="Person"/>

    </class>

</hibernate-mapping>

<?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 package="com.kaishengit.pojo">

    <class name="Person" table="person">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name"/>

        <!-- cascade="delete"表示删除人的时候把卡删了 -->

        <one-to-one cascade="delete" name="card" class="Card"/>

    </class>

</hibernate-mapping>

程序执行

        Person p = new Person();

        p.setUsername("tom");

        Card c = new Card();

        c.setCardnum("12");

        c.setPerson(p);

        session.save(p);

        session.save(c);

/* 这时候有两条sql,都是insert,改变save(p),save(c)的顺序式没用的

因为card的insert必须要有id,id不能为空,因为它作为主键,所以程序只能

先save(p)*/

        Person p = new Person();

        p.setUsername("tom");

        Card c = new Card();

        c.setCardnum("12");

        p.setCard(c);

        session.save(p);

        session.save(c);

/* 这样做就会报错了,因为主键的生成策略是从card找person属性

所以这种情况就只能让又当主键又当外键的那个表来维护关系 */

查询这种情况下的查询都是联接查询,有捆绑性

Card card = (Card) session.get(Card.class, 2);

        System.out.println(card.getCardnum());

        System.out.println(card.getPerson().getName());

        Person p = (Person) session.get(Person.class, 2);

        System.out.println(p.getName());

        System.out.println(p.getCard().getCardnum());

删除

<?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 package="com.kaishengit.pojo">

    <class name="Person" table="person">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name"/>

        <!-- cascade="delete"表示删除人的时候把卡删了 -->

        <one-to-one cascade="delete" name="card" class="Card"/>

    </class>

</hibernate-mapping>

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第二种一对一,是一对多或者多对一的特殊情况,具有延迟加载的能力

dept和Employee,dept中有eid,Employee中有deptid

// 各村对方的一个对象

public class Dept {

    private Integer id;

    private String name;

    private Employee employee;

}

public class Employee {

    private Integer id;

    private String name;

    private Dept dept;

}

xxx.hmb.xml的配置

<?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 package="com.kaishengit.pojo">

    <class name="Dept" table="dept">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name"/>

        <!-- 是多对一的特殊情况,需要指定unique="true"唯一性 -->

        <many-to-one name="employee" class="Employee" unique="true" column="eid"/>

    </class>

</hibernate-mapping>

<?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 package="com.kaishengit.pojo">

    <class name="Employee" table="employee">

        <id name="id">

            <generator class="native"/>

        </id>

        <property name="name"/>

        <!-- 是多对一的特殊情况,需要指定unique="true"唯一性 -->

        <many-to-one name="dept" class="Dept" unique="true" column="deptid"/>

    </class>

</hibernate-mapping>

程序执行

Employee e = new Employee();

        e.setName("jack");

        Dept d = new Dept();

        d.setName("hr");

        d.setEmployee(e);

        e.setDept(d);

        session.save(e);

        session.save(d);

请看这里,这是双向维护关系,而且必须双向维护关系,不可避免的会多一条update语句

巴特西

hibernate 数据关联一对一

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