Hibernate基础：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
[java]
@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;
    }

[java]
@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
[java]
@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();
}
[java]
@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
[java]
@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()
[java]
@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
[java] view plaincopy
@JoinColumn换成@PrimaryKeyJoinColumn//指定外键名字

补充：软件开发 , Java ,