Hibernate关联

一对一单向外键

@OneToOne ：一对一关联关系。
@JoinColumn (name = "id_card_id")：name指定关联的字段，其实就是指当前表的外键。

CREATE TABLE id_card(
	id INT AUTO_INCREMENT PRIMARY KEY,
	pid VARCHAR(18) NOT NULL COMMENT'身份证号',
	sname VARCHAR(255) NOT NULL COMMENT'姓名'
)ENGINE = INNODB AUTO_INCREMENT = 10 DEFAULT CHARSET = UTF8;

CREATE TABLE student(
	sid INT AUTO_INCREMENT PRIMARY KEY,
	id_card_id INT,
	gender VARCHAR(255) NOT NULL,
	INDEX index_id_card_id (id_card_id),
	CONSTRAINT fk_id_card_id FOREIGN KEY(id_card_id) REFERENCES id_card(id)ON DELETE CASCADE ON UPDATE CASCADE
)ENGINE = INNODB AUTO_INCREMENT = 10 DEFAULT CHARSET = UTF8;

package com.springboot.springbootlearning.dataobject;
import javax.persistence.*;
@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer sid;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "id_card_id" ,unique = true)
    private IdCard idCard;

    private String gender;

    public Student() {
    }

    public Student(IdCard idCard, String gender) {
        this.idCard = idCard;
        this.gender = gender;
    }

    //省略get和set
}

package com.springboot.springbootlearning.dataobject;
import javax.persistence.*;
@Entity
public class IdCard {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(length = 18)
    private String pid; //学生身份证号

    private String sname; //学生姓名

    public IdCard() {
    }

    public IdCard(String pid, String sname) {
        this.pid = pid;
        this.sname = sname;
    }

    //省略get和set
}

package com.springboot.springbootlearning.repository;

import com.springboot.springbootlearning.dataobject.IdCard;
import com.springboot.springbootlearning.dataobject.Student;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.util.Assert;

import java.util.ArrayList;
import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentRepositoryTest {

    @Autowired
    private StudentRepository studentRepository;

    @Test
    public void save()
    {
        List<Student> list = new ArrayList<>();

        IdCard idCard = new IdCard("123456789","张三");
        Student student1 = new Student(idCard,"男");
        list.add(student1);

        Student student2 = new Student();
        student2.setGender("女");
        list.add(student2);

        Assert.notNull(studentRepository.saveAll(list));
    }
}

一对一双向外键

只需要改变IdCard类的代码即可，其他代码与一对一单向外键一样。

@OneToOne(mappedBy="idCard")

双向关联，那么在IdCard类中也需要一个属性Student。@OneToOne表示身份证（IdCard）和学生（Student）是一对一的关系并且关联上学生（Student）。最后，mappedBy="idCard”，可以这么理解，mappedBy定义在关系的被拥有方，mappedBy定义所在的类（不管是单个还是集合的形式）在关系拥有者那一方的名称是“idCard"，例如在本例题里，Student类里面有一个IdCard属性，而该属性的名称就是“idCard"。

package com.springboot.springbootlearning.dataobject;
import javax.persistence.*;
@Entity
public class IdCard {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(length = 18)
    private String pid; //学生身份证号

    private String sname; //学生姓名

    @OneToOne(mappedBy = "idCard")
    private Student student;

    public IdCard() {
    }

    public IdCard(String pid, String sname) {
        this.pid = pid;
        this.sname = sname;
    }

    //省略get和set方法
}

一对一双向外键联合主键

1.创建主键类。

2.主键类必须实现Serializable接口，重写hashCode和equals()方法。

主键类：@Embeddable

实体类：@EmbeddedId