一对一关联映射

人和身份证之间就是一个典型的一对一关联关系。实现一对一关联关系映射的方式有两种一种是基于外键，一种是基于主键，下面我们先看基于外键的关联方式

首先看他们的实体类

Person类

package entity;
 
public class Person {
    private Integer id;
    private String name;
    private IdCard idCard;
    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 IdCard getIdCard() {
        return idCard;
    }
    public void setIdCard(IdCard idCard) {
        this.idCard = idCard;
    }
}

然后看IdCard类

package entity;
 
public class IdCard {
    private Integer id;
    private String number;
    private Person person;
     
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getNumber() {
        return number;
    }
    public void setNumber(String number) {
        this.number = number;
    }
    public Person getPerson() {
        return person;
    }
    public void setPerson(Person person) {
        this.person = person;
    }
     
     
}

这里在Person类和IdCard类中分别有一个对方类型的属性。

然后看他们之间的关联关系映射，首先看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">
 
<hibernate-mapping>
    <class name="entity.Person" table="Person" schema="MYHR">
        <id name="id" type="int">
            <column name="ID" />
            <generator class="assigned" />
        </id>
        <property name="name" type="string">
            <column name="NAME" not-null="true" />
        </property>
        <!-- idCard属性，IdCard类型，表达本类与IdCard的一对一关联 -->
        <!-- 采用基于外键的一对一，本方无外键方 -->
        <!-- property-ref属性：对方映射中外键类对应的属性名 -->
        <one-to-one name="idCard" class="entity.IdCard" property-ref="person"> 
        </one-to-one>
    </class>
</hibernate-mapping>

然后看一下IdCard.hbm.xml文档

<?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="entity.IdCard" table="IdCard" schema="MYHR">
        <id name="id">
            <column name="ID"/>
            <generator class="assigned" />
        </id>
        <property name="number">
            <column name="NAME" not-null="true" />
        </property>
        <!-- person属性，Person类型，表示与Person类的一对一关联关系 -->
        <!-- 采用基于外键的一对一关联方式，本方有外键 -->
        <many-to-one name="person" column="personId" class="entity.Person" unique="true"></many-to-one>
    </class>
</hibernate-mapping>

这样Person和IdCard之间的一对一关联关系就搭建好了

测试类

package test;
 
import static org.junit.Assert.*;
 
import org.hibernate.Session;
import org.hibernate.Transaction;
 
import entity.IdCard;
import entity.Person;
import factory.HibernateSessionFactory;
 
public class Test {
 
    private Session session = null;
    private Transaction tran = null;
    @org.junit.Test
    public void save() {
        session = HibernateSessionFactory.getSession();
        tran = session.beginTransaction();
        try{
            //新建对象
            Person p = new Person();
            p.setId(1);
            p.setName("张三");
             
            IdCard idCard = new IdCard();
            idCard.setId(1);
            idCard.setNumber("10001");
             
            p.setIdCard(idCard);
            idCard.setPerson(p);
             
            session.save(p);
            session.save(idCard);
             
            tran.commit();
        }catch(Exception e){
            tran.rollback();
        }
    }
 
    @org.junit.Test
    public void Get() {
        session = HibernateSessionFactory.getSession();
        tran = session.beginTransaction();
        try{
            Person person = (Person) session.get(Person.class, 1);
            IdCard idCard = person.getIdCard();
            System.out.println(person.getName()+"身份证号："+idCard.getNumber());
            tran.commit();
        }catch(Exception e){
            tran.rollback();
        }
    }
    //解除关系
    @org.junit.Test
    public void RemoveRelation() {
        session = HibernateSessionFactory.getSession();
        tran = session.beginTransaction();
        try{
            //从有外键方接触关联关系可以，不可以从无外键方解除
            IdCard idCard = (IdCard)session.get(IdCard.class, 1);
            idCard.setPerson(null);
            tran.commit();
        }catch(Exception e){
            tran.rollback();
        }
    }
    //删除
    @org.junit.Test
    public void DeleteRelation() {
        session = HibernateSessionFactory.getSession();
        tran = session.beginTransaction();
        try{
            //如果没有关联对方，可以直接删除。 
            //如果有关联对方，且可以维护关联关系，他就会先删除关联关系，在删除自己。
            //如果有关联关系，且不能维护关联关系，所以会执行删除自己，并且抛出异常。
            IdCard idCard = (IdCard)session.get(IdCard.class, 1);
            session.delete(idCard);
            tran.commit();
        }catch(Exception e){
            tran.rollback();
        }
    }
}

这就是基于外键方式，基于主键的方式只需要在以上基础修改一下映射文件即可，下面分别看一下修改后的映射文件

首先看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">
 
<hibernate-mapping package="entity">
    <class name="entity.Person" table="Person" schema="MYHR">
        <id name="id" type="int">
            <column name="ID" />
            <generator class="assigned" />
        </id>
        <property name="name" type="string">
            <column name="NAME" not-null="true" />
        </property>
        <!-- idCard属性，IdCard类型，表达本类与IdCard的一对一关联 -->
        <!-- 采用基于主键的一对一，本方无外键方 -->
        <one-to-one name="idCard" class="entity.IdCard"/>
       
    </class>
</hibernate-mapping>

然后看IdCard.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 package="entity">
    <class name="entity.IdCard" table="IdCard" schema="MYHR">
        <id name="id" type="int">
            <column name="ID" />
            <!-- 当使用基于主键的一对一映射时，有外键方的主键生成策略是foreign， -->
            <!-- 参数property：生成主键值时所根据的对象 -->
            <generator class="foreign">
                <param name="property">person</param>
            </generator>
        </id>
        <property name="number" type="string">
            <column name="NAME" not-null="true" />
        </property>
        <!-- person属性，Person类型，表示与Person类的一对一关联关系 -->
        <!-- 采用基于主键的一对一关联方式，本方有外键 -->
        <one-to-one name="person" class="entity.Person"
            constrained="true" />
    </class>
</hibernate-mapping>