07hibernate_one2one_ufk_1

hibernate一对一唯一外键关联映射（单向关联Person---->IdCard）

一对唯一外键关联映射是多对一关联映射的特例：

public class Person {

    private int id;
    
    private String name;
    
    private IdCard idCard; //在多的一方加入一个外键，数据库中增加一个字锻
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<hibernate-mapping>
    <class name="com.bjsxt.hibernate.Person" table="t_person">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <many-to-one name="idCard" unique="true"/>
    </class>
</hibernate-mapping>
    
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可以采用<many-to-one>标签，指定多的一端的unique=true，这样就限制了多的一端的多重性为一
通过这种手段映射一对一唯一外键关联
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导出表语句：
create table t_idcard (id integer not null auto_increment, cardNo varchar(255), primary key (id))

create table t_person (id integer not null auto_increment, name varchar(255), idCard integer unique, primary key (id))

alter table t_person add index FK785BED80539D4B66 (idCard), add constraint FK785BED80539D4B66 foreign key (idCard) references t_idcard (id)

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mysql> use 07hibernate_one2one_ufk_1;
Database changed
mysql> desc t_person;
+--------+--------------+------+-----+---------+----------------+
| Field  | Type         | Null | Key | Default | Extra          |
+--------+--------------+------+-----+---------+----------------+
| id     | int(11)      | NO   | PRI | NULL    | auto_increment |
| name   | varchar(255) | YES  |     | NULL    |                |
| idCard | int(11)      | YES  | UNI | NULL    |                |
+--------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> desc t_idcard;
+--------+--------------+------+-----+---------+----------------+
| Field  | Type         | Null | Key | Default | Extra          |
+--------+--------------+------+-----+---------+----------------+
| id     | int(11)      | NO   | PRI | NULL    | auto_increment |
| cardNo | varchar(255) | YES  |     | NULL    |                |
+--------+--------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

TestSave1:由于没有设置cascade="all",或者你只保存了多方，没有保存一方，则会抛出异常信息：org.hibernate.TransientObjectException
org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.bjsxt.hibernate.IdCard
TestSave1:
Hibernate: insert into t_idcard (cardNo) values (?)
Hibernate: insert into t_person (name, idCard) values (?, ?)

mysql> select *  FROM t_person;
+----+------+--------+
| id | name | idCard |
+----+------+--------+
|  2 | 菜10 |      1 |
+----+------+--------+
1 row in set (0.00 sec)

mysql> select *  FROM t_idcard;
+----+----------------+
| id | cardNo         |
+----+----------------+
|  1 | 88888888888888 |
+----+----------------+
1 row in set (0.00 sec)

TestLoad:
Hibernate: select person0_.id as id1_0_, person0_.name as name1_0_, person0_.idCard as idCard1_0_ from t_person person0_ where person0_.id=?
person.name=菜10
Hibernate: select idcard0_.id as id0_0_, idcard0_.cardNo as cardNo0_0_ from t_idcard idcard0_ where idcard0_.id=?
idCard.cardNo=88888888888888
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package com.bjsxt.hibernate;

import org.hibernate.Session;

import junit.framework.TestCase;

public class One2OneTest extends TestCase {

    public void testSave1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            IdCard idCard = new IdCard();
            idCard.setCardNo("88888888888888");
            
            Person person = new Person();
            person.setName("猪八戒");
            person.setIdCard(idCard);
            
            //不能成功保存，因为IdCard是Transient状态
            session.save(person);
            
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }        
    
    public void testSave2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            IdCard idCard = new IdCard();
            idCard.setCardNo("88888888888888");

           //先保存一方,再保存多方，OK！ 
            session.save(idCard);
            
            Person person = new Person();
            person.setName("菜10");
            person.setIdCard(idCard);
            
            session.save(person);
            
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }            
    public void testLoad1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
             //由于 testSave1()抛出异常，所以数据库中的记录id=2 
            Person person = (Person)session.load(Person.class, 2);
            System.out.println("person.name=" + person.getName());
            System.out.println("idCard.cardNo=" + person.getIdCard().getCardNo());
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }
    }        
    
}