关于OneToOne的一些话题

最新推荐文章于 2023-12-05 11:03:05 发布

iteye_7092

最新推荐文章于 2023-12-05 11:03:05 发布

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文章标签： Hibernate SQL

本文通过实战案例介绍了Hibernate框架中OneToOne关联映射的具体应用，包括数据的读写、更新和删除操作，并对比了不同场景下产生的SQL语句及其效率。

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对于hibernate的OneToOne我在实际的项目中并没有真正的使用过,这里只是做一些简单的了解,假设有如下两个数据库表:
IDCARDS[id varchar2(64) not null,
        card_no varchar2(100) not null,
        person_id varchar2(64) not null
       ]
person[id varchar2(64) not null,varchar2(100) name]

当前可以确定的操作有:
     读数据:
         读取person,
         读取idcard,
     写数据:
         写person信息到数据库中
         写idcard信息到数据库
     更新数据:
         更新person数据
         更新idcard信息数据
     删除数据:
         删除person数据信息
         删除idcard数据信息

    统计数据:
        统计person的总数

按照上面的需求,设计类文件如下,这里我们选择使用OneToOne:

@Entity
@Table(name="IDCARDS")
public class IDCard implements Serializable {
private static final long serialVersionUID = 1L;
private String id;
private String cardNo;
private Person person;
/**
* @return Returns the person.
*/
@OneToOne(optional=true,cascade=CascadeType.ALL,fetch=FetchType.LAZY)
@JoinColumn(name="person_id")
public Person getPerson() {
return person;
}
......
}
@Entity
@Table(name="persons")
public class Person implements Serializable {
private static final long serialVersionUID = 1L;
private String id;
private String name;
private IDCard idCard;
/**
* @return Returns the idCard.
*/
@OneToOne(optional=true,cascade=CascadeType.ALL,mappedBy="person",fetch=FetchType.LAZY)
public IDCard getIdCard() {
return idCard;
}
.......
}

写数据的测试:

public static void testOneToOne3(){
Person person = new Person();
person.setId("0001");
person.setName("snowflower");
IDCard card = new IDCard();
card.setId("123456");
card.setCardNo("123456789012");
card.setPerson(person);
Transaction tx = session.beginTransaction();
tx.begin();
session.save(person);
session.save(card);
session.flush();
tx.commit();
}

这种情况下执行的语句为:

　
更新数据:

public static void testOneToOne4(){
IDCard card = (IDCard)session.load(IDCard.class,"123456");
if(card != null){
card.setCardNo("new"+card.getCardNo());
}
Transaction tx = session.beginTransaction();
tx.begin();
session.update(card);
session.flush();
tx.commit();
}

在这里尝试更新IDCard的数据信息时hibernate产生的sql语句为：
Hibernate: select idcard0_.id as id2_1_,
　　　　　　　　idcard0_.card_no as card2_2_1_,
idcard0_.person_id as person3_2_1_,
person1_.id as id1_0_,
person1_.name as name1_0_
from
IDCARDS idcard0_
left outer join
persons person1_
on
idcard0_.person_id=person1_.id where idcard0_.id=?
Hibernate: select idcard0_.id as id2_1_,
idcard0_.card_no as card2_2_1_,
idcard0_.person_id as person3_2_1_,
person1_.id as id1_0_,
person1_.name as name1_0_
from
IDCARDS idcard0_
left outer join
persons person1_
on
idcard0_.person_id=person1_.id where idcard0_.person_id=?
Hibernate: update IDCARDS set card_no=?, person_id=? where id=?
感觉更新了一个IDCard的编号却牵连到如此语句,从某中意义上说,一条update语句足够了…………
为了改变更新的效率尝试如下的做法：

public static void testOneToOne4(){
Person person = (Person)session.load(Person.class,"0001");
IDCard card = person.getIdCard();
Transaction tx = session.beginTransaction();
tx.begin();
card.setCardNo("new"+card.getCardNo());
session.update(card);
session.flush();
tx.commit();
}

使用此种方法后生成的语句为：
Hibernate: select person0_.id as id1_1_,
                                person0_.name as name1_1_,
                                idcard1_.id as id2_0_,
                                idcard1_.card_no as card2_2_0_,
                                idcard1_.person_id as person3_2_0_
                   from
                                persons person0_
                   left outer join
                                IDCARDS idcard1_
                   on
                                person0_.id=idcard1_.person_id where person0_.id=?
Hibernate: update IDCARDS set card_no=?, person_id=? where id=?
这里需要注意的一点就是，如果IDCard数据没有改变的话是不会产生update语句的