Hibernate基础之八：一对一单/双向，主/外键关联 @OneToOne@JoinColumn

1：一对一，单向，外键关联

Student和stusentIDCard两张表是一对一的关系，即一个学生只有一个学生证，一个学生证只对应一个学生

Stuent表里有个外键要参考StudentIDCard

表现类上就是Student实例里聚合一个stusentIDCard

@Entity
public class Student
{
private int id;
private String name;
private int age;
private StudentIDCard cardId;

@Id
@GeneratedValue//可以定单独的自增序列，这共用一个
public int getId() {
return id;
}
@OneToOne//一对一的关系
@JoinColumn(name="card_Id")//指定外键名称是card_Id
public StudentIDCard getCardId() {
return cardId;
}

@Entity
public class StudentIDCard
{
private int id;
private String kinds;
private Date datePublished;

@Id
@GeneratedValue//可以定义单独的自增序列，这里共用一个
public int getId() {
return id;
}

测试类

@Test
public void testIN() {
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();

StudentIDCard sic = new StudentIDCard();
sic.setKinds("primarySchool");
sic.setDatePublished(new Date());
session.save(sic);

Student s = new Student();
s.setName("李四");
s.setAge(0);
s.setCardId(sic);
session.save(s);

session.getTransaction().commit();
HibernateUtil.getSessionFactory().close();
}

@Test
public void testShow() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false,true);
}

建表结果：

foreign key (card_Id) references StudentIDCard

16:15:13,184 DEBUG SchemaUpdate:226 - create table Student (id number(10,0) not null, age number(10,0) not null, name varchar2(255 char), card_Id number(10,0),primary
key (id))

16:15:13,193 DEBUG SchemaUpdate:226 - create table StudentIDCard (id number(10,0) not null, datePublished timestamp, kinds varchar2(255 char), primary key (id))

16:15:13,200 DEBUG SchemaUpdate:226 - alter table Student add constraint FKF3371A1BEA113360foreign key (card_Id)references StudentIDCard

PowerDesigner里反向工程出来的图如下：



就是Student表里的字段要去参考StudenIDCard表里的东西，外键名字我指定的是：“CARD_ID”

2：一对一，双向，外键关联

双向表现在类上就是：Student和stusentIDCard互相聚合一个实例，

双方都标注@OneToOne

Student类不变，参考上边那个，不赘述了

@Entity
public class StudentIDCard
{
private int id;
private String kinds;
private Date datePublished;
private Student student;

@Id
@GeneratedValue
public int getId() {
return id;
}
@OneToOne//互相持有，都加了OneToOne
public Student getStudent() {
return student;
}

但这样就等于会在表里出现重复的字段，还要设置mappedBy，说明对方是主导，消除冗余

StudentIDCard类的getStudent()上

@OneToOne(mappedBy="StudentIDCard")说明对方是主导，对方(Student)的"cardId"属性已经做映射了，消除互相是外键的冗余

getStudent()

@OneToOne(mappedBy="cardId")//说明对方是主导，对方(Student)的"cardId"属性已经做映射了，消除互相是外键的冗余
public Student getStudent() {
return student;
}

3：一对一，单向，主键关联

@JoinColumn换成@PrimaryKeyJoinColumn//指定外键名字

@JoinColumn换成@PrimaryKeyJoinColumn//指定外键名字