SpringDataJpa的使用之一对一、一对多、多对多 关系映射问题

2022-11-13 12:11:42 关系 映射 SpringDataJpa

SpringDataJpa的使用 -- 一对一、一对多、多对多 关系映射

本文主要讲述 @OneToOne、@OneToMany、@ManyToOne、@ManyToMany 这四个关系映射注解的使用，以及其对应的级联关系

有四张表，分别是：学生表、家长表、教室表、教师表，它们的关联关系如下：

  • 学生 对 家长：一对一
  • 学生 对 教室：多对一
  • 学生 对 教师：多对多

项目依赖

必要的依赖有：mysql驱动、SpringBootWEB、SpringBootStarter、SpringDataJpa、SpringBootText、druid，其它的依赖可以按需添加。 如：lombok、

pom.xml 必要依赖

<!-- Spring Boot 都使用 2.4.5，看个人习惯 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <version>2.4.5</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>2.4.5</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-test</artifactId>
<version>2.4.5</version>
<scope>runtime</scope>
</dependency>
<!-- Spring Data JPA 使用 2.6.1，看个人习惯 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
<version>2.6.1</version>
</dependency>

<!-- mysql 驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.25</version>
<scope>runtime</scope>
</dependency>
<!-- druid 数据库连接池 -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>1.1.24</version>
</dependency>

pom.xml 可选依赖

<!--  Spring 热部署  -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <version>2.4.5</version>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>
<!-- lombok -->
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.20</version>
<optional>true</optional>
</dependency>

项目配置

application.yaml

spring:
  # DataSource
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: 账号
    passWord: 密码
    # serverTimezone可以设置为北京时间GMT%2B8、上海时间Asia/Shanghai或者香港时间Hongkong
    url: jdbc:mysql://localhost:3306/cloudtext?useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT%2B8
  # DataBase Connection -- JPA
  jpa:
    # 显示 SQL 语句
    show-sql: true
    # 不允许在视图阶段 执行 sql
    open-in-view: false

# 建议设置一个不常用的，避免冲突
server:
  # 项目端口号
  port: 8092
  # 项目路径
  servlet:
    context-path: /jpa

sql文件（MySQL版）

cloudText.sql 仅结构

-- ----------------------------
-- Table structure for classroom
-- ----------------------------
DROP TABLE IF EXISTS `classroom`;
CREATE TABLE `classroom` (
 `class_room_id` tinyint unsigned NOT NULL AUTO_INCREMENT COMMENT '班级主键',
 `class_room_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL COMMENT '班级名称',
 `class_room_location` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL COMMENT '班级位置',
  `class_room_capacity` int unsigned DEFAULT NULL COMMENT '班级人数',
  `class_room_grade` varchar(255) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL COMMENT '班级年级',
 PRIMARY KEY (`class_room_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb3 COLLATE=utf8_bin;

-- ----------------------------
-- Table structure for patriarch
-- ----------------------------
DROP TABLE IF EXISTS `patriarch`;
CREATE TABLE `patriarch` (
 `patriarch_id` tinyint unsigned NOT NULL AUTO_INCREMENT COMMENT '家长主键',
 `patriarch_name` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '家长姓名',
 `patriarch_age` int unsigned DEFAULT NULL COMMENT '家长年龄',
 `patriarch_sex` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '家长性别',
 `patriarch_phone` varchar(11) COLLATE utf8_bin DEFAULT NULL COMMENT '家长电话',
 `patriarch_address` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '家长住址',
 PRIMARY KEY (`patriarch_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb3 COLLATE=utf8_bin;

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
 `student_id` tinyint unsigned NOT NULL AUTO_INCREMENT COMMENT '学生主键',
 `student_name` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '学生姓名',
 `student_age` int unsigned DEFAULT NULL COMMENT '学生年龄',
 `student_sex` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '学生性别',
 `patriarch_id` tinyint unsigned NOT NULL COMMENT '家长外键',
 `class_room_id` tinyint unsigned DEFAULT NULL COMMENT '班级外键',
 PRIMARY KEY (`student_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb3 COLLATE=utf8_bin;

-- ----------------------------
-- Table structure for student_teacher
-- ----------------------------
DROP TABLE IF EXISTS `student_teacher`;
CREATE TABLE `student_teacher` (
 `student_id` tinyint unsigned NOT NULL COMMENT '学生主键',
 `teacher_id` tinyint unsigned NOT NULL COMMENT '教师主键',
 PRIMARY KEY (`student_id`,`teacher_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3 COLLATE=utf8_bin;


-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
 `teacher_id` tinyint unsigned NOT NULL AUTO_INCREMENT COMMENT '教师主键',
 `teacher_name` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '教师姓名',
 `teacher_age` int unsigned DEFAULT NULL COMMENT '教师年龄',
 `teacher_sex` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '教师性别',
 `teacher_course` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '教师教授科目',
 PRIMARY KEY (`teacher_id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb3 COLLATE=utf8_bin;

级联关系简述

  • ALL -- 级联所有操作
  • PERSIST -- 级联持久化操作
  • MERGE -- 级联合并操作
  • REMOVE -- 级联删除操作
  • REFRESH -- 级联刷新操作（调用refresh方法才会刷新）
  • DETACH -- 级联分离操作（2.0版本才有）

参考：《Spring Boot 整合——JPA 数据模型关联操作（一对一、一对多、多对多）》

参考：《cascade级联关系》

@OneToOne 一对一 关系映射

一对一关系的双方必须有且仅有一方放弃维护，在 @OneToOne 中添加mappedBy属性表示放弃维护。

学生类（Student.java）：维护方 家长类（Patriarch.java）：被维护方

Student.java (主键和非外键属性)

package com.ljm.exmaple.entity;

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToOne;
import javax.persistence.Table;


@Entity
@Table(name = "STUDENT")
public class Student {
	
	
	@Id
	@Column(name = "student_id", nullable = false)
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Long studentId;
	
	@Column(name = "student_name", nullable = false)
	private String studentName;
	
	@Column(name = "student_age", nullable = false)
	private Short studentAge;
	
	@Column(name = "student_sex", nullable = false)
	private String studentSex;
	
}

Patriarch.java (主键和非外键属性)

package com.ljm.exmaple.entity;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;


@Entity
@Table(name = "PATRIARCH")
public class Patriarch {
    
    @Id
    @Column(name = "patriarch_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long patriarchId;
    
    @Column(name = "patriarch_name", nullable = false)
    private String patriarchName;
    
    @Column(name = "patriarch_age")
    private Short patriarchAge;
    
    @Column(name = "patriarch_sex", nullable = false)
    private String patriarchSex;
    
    @Column(name = "patriarch_phone", nullable = false, length = 11)
    private String patriarchPhone;
    
    @Column(name = "patriarch_address", nullable = false)
    private String patriarchAddress;
    
}

1.无中间表，维护方添加外键，被维护方添加对应项

cascade = CascadeType.ALL 表示：级联关系。

fetch = FetchType.EAGER 表示：预加载。

name = "patriarch_id" 指定外键。

nullable = false 表示：不能为空。

unique = true 表示：不能重复。

mappedBy = "patriarch" ：添加了这个属性表示放弃维护。

维护方的属性添加到 Student.java 中。

被维护方的属性添加到 Patriarch.java 中。


@OneToOne(cascade = {CascadeType.MERGE, CascadeType.REMOVE}, fetch = FetchType.EAGER)
@JoinColumn(name = "patriarch_id", nullable = false, unique = true)
private Patriarch patriarch;



@OneToOne(mappedBy = "patriarch", cascade = {CascadeType.REFRESH, CascadeType.MERGE, CascadeType.REMOVE}, fetch = FetchType.EAGER)
private Student student;

2.无中间表，维护方添加外键，被维护方不添加对应项

cascade = CascadeType.ALL 表示：级联关系。

fetch = FetchType.EAGER 表示：预加载。

name = "patriarch_id" 指定外键。

nullable = false 表示：不能为空。

unique = true 表示：不能重复。

维护方的属性添加到 Student.java 中。


@OneToOne(cascade = {CascadeType.MERGE, CascadeType.REMOVE}, fetch = FetchType.EAGER)
@JoinColumn(name = "patriarch_id", nullable = false, unique = true)
private Patriarch patriarch;

3.有中间表，维护方不添加外键，被维护方不添加对应项

暂缺，这不是本文重点，以后可能会添加。

不需要使用关系注解 @OneToOne、@OneToMany、@ManyToOne、@ManyToMany，没有外键。

@OneToMany、@ManyToOne 一对多 关系映射

一对多关系中，多方必须维护外键，一方一般不维护（我在某篇文章中看到：说一方也可以维护外键，我还未验证）。

学生类（Student.java）：维护方

教室类（ClassRoom.java）：被维护方

Student.java (主键和非外键属性)

package com.ljm.exmaple.entity;

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToOne;
import javax.persistence.Table;


@Entity
@Table(name = "STUDENT")
public class Student {
    
    @Id
    @Column(name = "student_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long studentId;
    
    @Column(name = "student_name", nullable = false)
    private String studentName;
    
    @Column(name = "student_age", nullable = false)
    private Short studentAge;
    
    @Column(name = "student_sex", nullable = false)
    private String studentSex;
    
}

ClassRoom.java (主键和非外键属性)

package com.ljm.exmaple.entity;

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;


@Entity
@Table(name = "CLASSROOM")
public class ClassRoom {
    
    @Id
    @Column(name = "classRoom_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long classRoomId;
    
    @Column(name = "classRoom_name", nullable = false)
    private String classRoomName;
    
    @Column(name = "classRoom_location", nullable = false)
    private String classRoomLocation;
    
    @Column(name = "classRoom_capacity", nullable = false)
    private Short classRoomCapacity;
    
    @Column(name = "classRoom_grade", nullable = false)
    private String classRoomGrade;
    
}

1.无中间表，多方维护并添加外键，一方被维护

cascade = CascadeType.XXX 表示：级联关系。

fetch = FetchType.EAGER 表示：预加载。

name = "classRoom_id" 指定外键。

nullable = false 表示：不能为空。

mappedBy = "classRoom" ：添加了这个属性表示放弃维护，在一对多的一方用来指向多方的那个外键属性。


@JoinColumn(name = "classRoom_id", nullable = false)
@ManyToOne(fetch = FetchType.EAGER)
private ClassRoom classRoom;



@OneToMany(mappedBy = "classRoom", cascade = {CascadeType.MERGE, CascadeType.REFRESH}, fetch = FetchType.EAGER)
private List<Student> studentList;

2.有中间表，多方维护，一方被维护

暂缺，这不是本文重点，以后可能会添加。

不需要使用关系注解 @OneToOne、@OneToMany、@ManyToOne、@ManyToMany，没有外键。

3.无中间表，多方维护，一方也维护

暂缺，待验证。

@ManyToMany 多对多 关系映射

多对多关系中，必须有且仅有一方放弃维护外键，需要新建中间表，但不需要写对应的实体类。

学生类（Student.java）：维护方

教师类（Teacher.java）：被维护方

Student.java (主键和非外键属性)

package com.ljm.exmaple.entity;

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.ManyToOne;
import javax.persistence.OneToOne;
import javax.persistence.Table;


@Entity
@Table(name = "STUDENT")
public class Student {	
    
    @Id
    @Column(name = "student_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long studentId;
    
    @Column(name = "student_name", nullable = false)
    private String studentName;
    
    @Column(name = "student_age", nullable = false)
    private Short studentAge;
    
    @Column(name = "student_sex", nullable = false)
    private String studentSex;
    
}

Teacher.java (主键和非外键属性)

package com.ljm.exmaple.entity;
import java.util.List;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name = "TEACHER")
public class Teacher {
    
    @Id
    @Column(name = "teacher_id", nullable = false)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long teacherId;
    
    @Column(name = "teacher_name", nullable = false)
    private String teacherName;
    
    @Column(name = "teacher_age")
    private Integer teacherAge;
    
    @Column(name = "teacher_sex", nullable = false)
    private String teacherSex;
    
    @Column(name = "teacher_course", nullable = false)
    private String teacherCourse;
    
}

fetch = FetchType.EAGER 表示：预加载。

name = "student_teacher" 指定关联关系表。

joinColumns = @JoinColumn(name = "student_id") 指定我方在关联表中对应的主键。

inverseJoinColumns = @JoinColumn(name = "teacher_id") 指定被维护方在关联表中对应的主键。

mappedBy = "teacherList" ：添加了这个属性表示放弃维护，维护方用来指向另一方的那个外键属性。


@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "student_teacher", joinColumns = @JoinColumn(name = "student_id"), inverseJoinColumns = @JoinColumn(name = "teacher_id"))
private List<Teacher> teacherList;



@ManyToMany(mappedBy = "teacherList", fetch = FetchType.EAGER)
private List<Student> studentList;

本文参考

Spring Data JPA之一对一，一对多，多对多关系映射

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