jpa一对一映射案例
双向和单向的区别，其实不在数据库，而在加载方向。如Person和IdCard，单向是Person拥有IdCard的实例可以加载IdCard，而双向不但Person可以加载IdCard，IdCard可以拥有Person实例来加载Person。数据库还是原来的数据库(两个共享主键的表)
以下模拟双向一对一得映射案例
表结构如下：
Person表结构
IdCard表结构
IDCard类
package
com.ljq.entity;
import
javax.persistence.CascadeType;
import
javax.persistence.Column;
import
javax.persistence.Entity;
import
javax.persistence.GeneratedValue;
import
javax.persistence.Id;
import
javax.persistence.JoinColumn;
import
javax.persistence.OneToOne;
import
javax.persistence.Table;
/**
* 身份证
*
*
@author
jiqinlin
*
*/
@Entity
@Table(name
=
"
tb_idcard
"
)
public
class
IDCard {
@Id
@GeneratedValue
private
Integer id;
@Column(nullable
=
false
, length
=
18
)
private
String cardno;
//
unique= true 指明personid列的值不可重复。
//
optional = false指明Person不可为空
@OneToOne(cascade
=
CascadeType.ALL, optional
=
false
)
@JoinColumn(name
=
"
personid
"
,referencedColumnName
=
"
id
"
, unique
=
true
)
private
Person person;
public
IDCard() {
super
();
}
public
IDCard(String cardno) {
super
();
this
.cardno
=
cardno;
}
public
String getCardno() {
return
cardno;
}
public
void
setCardno(String cardno) {
this
.cardno
=
cardno;
}
public
Integer getId() {
return
id;
}
public
void
setId(Integer id) {
this
.id
=
id;
}
public
Person getPerson() {
return
person;
}
public
void
setPerson(Person person) {
this
.person
=
person;
}
}
Person类
package
com.ljq.entity;
import
javax.persistence.CascadeType;
import
javax.persistence.Column;
import
javax.persistence.Entity;
import
javax.persistence.GeneratedValue;
import
javax.persistence.Id;
import
javax.persistence.OneToOne;
import
javax.persistence.Table;
/**
* 人
*
*
@author
jiqinlin
*
*/
@Entity
@Table(name
=
"
tb_person
"
)
public
class
Person {
@Id
@GeneratedValue
private
Integer id;
@Column(nullable
=
false
, length
=
20
)
private
String name;
//
optional = false指明IDCard可为空
//
mappedBy="person"指明Person作为双向关系的维护段，负责外键的更新，起主导作用
@OneToOne(optional
=
true
, cascade
=
CascadeType.ALL, mappedBy
=
"
person
"
)
private
IDCard idcard;
public
Person() {
super
();
}
public
Person(String name) {
super
();
this
.name
=
name;
}
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;
}
}
OneToOneTest测试类
package
com.ljq.test;
import
java.util.List;
import
javax.persistence.EntityManager;
import
javax.persistence.EntityManagerFactory;
import
javax.persistence.Persistence;
import
org.junit.Test;
import
com.ljq.entity.IDCard;
import
com.ljq.entity.Person;
public
class
OneToOneTest {
/**
* 添加人的时候同时添加对应的身份证
*/
@Test
public
void
save() {
EntityManagerFactory factory
=
Persistence.createEntityManagerFactory(
"
ljq
"
);
EntityManager em
=
factory.createEntityManager();
em.getTransaction().begin();
Person person
=
new
Person();
person.setName(
"
lisi
"
);
IDCard idcard
=
new
IDCard();
idcard.setCardno(
"
350524
"
);
idcard.setPerson(person);
person.setIdcard(idcard);
em.persist(person);
em.getTransaction().commit();
em.close();
factory.close();
}
/**
* 删除
*/
@Test
public
void
delete() {
EntityManagerFactory factory
=
Persistence.createEntityManagerFactory(
"
ljq
"
);
EntityManager em
=
factory.createEntityManager();
em.getTransaction().begin();
//
删除人同时会自动删除身份证
em.remove(em.getReference(Person.
class
,
2
));
//
删除身份证同时删除人
//
em.remove(em.getReference(IDCard.class, (Serializable)1));
em.getTransaction().commit();
em.close();
factory.close();
}
/**
* 更新
*/
@SuppressWarnings(
"
unchecked
"
)
@Test
public
void
update() {
EntityManagerFactory factory
=
Persistence.createEntityManagerFactory(
"
ljq
"
);
EntityManager em
=
factory.createEntityManager();
em.getTransaction().begin();
List
<
Person
>
persons
=
em.createQuery(
"
select o from Person o
"
).getResultList();
for
(Person person:persons){
person.setName(
"
wangwu
"
);
IDCard idcard
=
person.getIdcard();
if
(idcard
!=
null
){
idcard.setCardno(
"
abc
"
);
}
em.merge(person);
}
em.getTransaction().commit();
em.close();
factory.close();
}
/**
* 用来判断映射是否成功
*
*/
@Test
public
void
test() {
Persistence.createEntityManagerFactory(
"
ljq
"
);
}
}