Spring Boot JPA @OneToMany @ManyToOne 雙向映射

本文介紹 Spring Boot JPA @OneToMany 和 @ManyToOne 雙向映射的使用方法捶朵。

開發(fā)環(huán)境

JDK 8
MySQL 8

基礎(chǔ)示例

創(chuàng)建數(shù)據(jù)表。

CREATE SCHEMA `test` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin;

USE `test`;

CREATE TABLE `student` (
  `id`        BIGINT     UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主鍵',
  `number`    CHAR(10)            NOT NULL                COMMENT '學(xué)號',
  `name`      VARCHAR(30)         NOT NULL                COMMENT '姓名',
  PRIMARY KEY (`id`),
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) VISIBLE,
  UNIQUE INDEX `number_UNIQUE` (`number` ASC) VISIBLE)
COMMENT = '學(xué)生表';

CREATE TABLE `class` (
  `id`     BIGINT      UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主鍵',
  `name`   VARCHAR(30)          NOT NULL                COMMENT '班級名稱',
  PRIMARY KEY (`id`),
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) VISIBLE)
COMMENT = '班級表';

CREATE TABLE `class_t_student` (
  `id`         BIGINT UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主鍵',
  `class_id`   BIGINT          NOT NULL                COMMENT '班級主鍵ID',
  `student_id` BIGINT          NOT NULL                COMMENT '學(xué)生主鍵ID',
  PRIMARY KEY (`id`),
  UNIQUE INDEX `id_UNIQUE` (`id` ASC) VISIBLE,
  UNIQUE INDEX `class_student_UNIQUE` (`class_id` ASC, `student_id` ASC) VISIBLE)
COMMENT = '班級學(xué)生關(guān)聯(lián)關(guān)系表';

如何創(chuàng)建 Spring Boot JPA 工程請參考：http://www.reibang.com/p/e2b64d5c6107
創(chuàng)建 PO（Persistence Object）對象。

package tutorial.spring.boot.domain;

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;

@Entity
@Table(name = "class")
public class ClassPO {

    /**
     * 自增主鍵
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    /**
     * 姓名
     */
    private String name;

    /**
     * 學(xué)生
     */
    @OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.REMOVE})
    @JoinTable(name = "class_t_student",
            joinColumns = @JoinColumn(name = "class_id"),
            inverseJoinColumns = @JoinColumn(name = "student_id"))
    private List<StudentPO> students;

    // Getter涌韩、Setter 和 toString 方法略
}

package tutorial.spring.boot.domain;

import javax.persistence.*;

@Entity
@Table(name = "student")
public class StudentPO {

    /**
     * 自增主鍵
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    /**
     * 學(xué)號
     */
    private String number;

    /**
     * 姓名
     */
    private String name;

    /**
     * 所屬班級
     */
    @ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE})
    @JoinTable(name = "class_t_student",
            joinColumns = @JoinColumn(name = "student_id"),
            inverseJoinColumns = @JoinColumn(name = "class_id"))
    private ClassPO theClass;

    // Getter瘪匿、Setter 和 toString 方法略
}

創(chuàng)建繼承 JpaRepository 的 Repository 接口類莹菱。

package tutorial.spring.boot.dao;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import tutorial.spring.boot.domain.ClassPO;

@Repository
public interface ClassRepository extends JpaRepository<ClassPO, Long> {
}

package tutorial.spring.boot.dao;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import tutorial.spring.boot.domain.StudentPO;

@Repository
public interface StudentRepository extends JpaRepository<StudentPO, Long> {
}

編寫單元測試鞭呕。

package tutorial.spring.boot.dao;

import org.apache.commons.lang3.RandomStringUtils;
import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.MethodOrderer;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestMethodOrder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.dao.InvalidDataAccessApiUsageException;
import tutorial.spring.boot.domain.ClassPO;
import tutorial.spring.boot.domain.StudentPO;

import java.util.Collections;

@SpringBootTest
@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
class RepositoryTest {

    @Autowired
    private ClassRepository classRepository;

    @Autowired
    private StudentRepository studentRepository;

    @Test
    @Order(1)
    void testInsertStudent() {
        // class 和 student 表中都沒有記錄
        Assertions.assertThat(classRepository.count()).isEqualTo(0);
        Assertions.assertThat(studentRepository.count()).isEqualTo(0);
        // 創(chuàng)建 class 和 student 實(shí)體對象并將其綁定起來
        ClassPO theClass = new ClassPO();
        theClass.setName(RandomStringUtils.randomAlphanumeric(1, 10));
        StudentPO student = new StudentPO();
        student.setNumber(RandomStringUtils.randomAlphanumeric(10));
        student.setName(RandomStringUtils.randomAlphanumeric(2, 20));
        student.setTheClass(theClass);
        // 因?yàn)?student 級聯(lián)類型為 CascadeType.MERGE，所以級聯(lián)新增會產(chǎn)生異常
        Assertions.assertThatThrownBy(() -> studentRepository.save(student))
                .isInstanceOf(InvalidDataAccessApiUsageException.class);
        // 去除關(guān)聯(lián)關(guān)系篇恒，只保存 student 成功
        student.setTheClass(null);
        studentRepository.save(student);
    }

    @Test
    @Order(2)
    void testInsertClass() {
        // 依賴于之前的單元測試扶檐，此時 student 表中有一條記錄，class 表中無記錄
        Assertions.assertThat(classRepository.count()).isEqualTo(0);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        // 創(chuàng)建 class 和 student 實(shí)體對象并將其綁定起來
        ClassPO theClass = new ClassPO();
        theClass.setName(RandomStringUtils.randomAlphanumeric(1, 10));
        StudentPO student = new StudentPO();
        student.setNumber(RandomStringUtils.randomAlphanumeric(10));
        student.setName(RandomStringUtils.randomAlphanumeric(2, 20));
        theClass.setStudents(Collections.singletonList(student));
        // 因?yàn)?class 級聯(lián)類型為 CascadeType.REMOVE婚度，所以級聯(lián)新增會產(chǎn)生異常
        Assertions.assertThatThrownBy(() -> classRepository.save(theClass))
                .isInstanceOf(InvalidDataAccessApiUsageException.class);
        // 去除關(guān)聯(lián)關(guān)系蘸秘，只保存 class 成功
        theClass.setStudents(null);
        classRepository.save(theClass);
    }

    @Test
    @Order(3)
    void testUpdateStudent() {
        // 依賴于之前的單元測試，此時 class 和 student 表中應(yīng)各有一條記錄
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        ClassPO theClass = classRepository.findAll().get(0);
        StudentPO student = studentRepository.findAll().get(0);
        // 綁定并保存關(guān)聯(lián)關(guān)系
        student.setTheClass(theClass);
        studentRepository.save(student);
        // 更新 class 數(shù)據(jù)
        String originalClassName = theClass.getName();
        Assertions.assertThat(student.getTheClass().getName()).isEqualTo(originalClassName);
        // 通過保存 student 級聯(lián)更新 class蝗茁，因?yàn)?student 級聯(lián)類型為 CascadeType.MERGE醋虏，所以級聯(lián)更新成功
        student.getTheClass().setName(originalClassName + RandomStringUtils.randomAlphabetic(1));
        studentRepository.save(student);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        StudentPO findStudent = studentRepository.findAll().get(0);
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        ClassPO findClass = classRepository.findAll().get(0);
        Assertions.assertThat(findStudent.getTheClass().getName())
                .isEqualTo(findClass.getName())
                .isNotEqualTo(originalClassName);
    }

    @Test
    @Order(4)
    void testUpdateClass() {
        // 依賴于之前的單元測試，此時 class 和 student 表中應(yīng)各有一條記錄
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        ClassPO theClass = classRepository.findAll().get(0);
        StudentPO student = studentRepository.findAll().get(0);
        // 更新 student 數(shù)據(jù)
        String studentName = student.getName();
        Assertions.assertThat(theClass.getStudents().get(0).getName()).isEqualTo(studentName);
        // 通過保存 class 級聯(lián)更新 student哮翘，因?yàn)?class 級聯(lián)類型為 CascadeType.REMOVE颈嚼，所以級聯(lián)更新失敗，student 數(shù)據(jù)不會改變
        theClass.getStudents().get(0).setName(studentName + RandomStringUtils.randomAlphabetic(1));
        classRepository.save(theClass);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        StudentPO findStudent = studentRepository.findAll().get(0);
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        Assertions.assertThat(findStudent.getName()).isEqualTo(studentName);
    }

    @Test
    @Order(5)
    void testDelete() {
        // 依賴于之前的單元測試饭寺，此時 class 和 student 表中應(yīng)各有一條記錄
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        Assertions.assertThat(studentRepository.count()).isEqualTo(1);
        // 執(zhí)行刪除 student 操作阻课，因?yàn)?student 級聯(lián)類型為 CascadeType.MERGE叫挟，所以只會刪除自己和關(guān)聯(lián)表記錄，無法刪除 class
        StudentPO student = studentRepository.findAll().get(0);
        studentRepository.delete(student);
        Assertions.assertThat(classRepository.count()).isEqualTo(1);
        Assertions.assertThat(studentRepository.count()).isEqualTo(0);
        /*
         * 執(zhí)行刪除 class 操作限煞，因?yàn)?class 級聯(lián)類型為 CascadeType.REMOVE抹恳，所以會刪除自己及關(guān)聯(lián)的 student 記錄
         * 為了驗(yàn)證級聯(lián)刪除效果，需要將屏蔽刪除 student 操作的代碼段
         */
        ClassPO theClass = classRepository.findAll().get(0);
        classRepository.delete(theClass);
        Assertions.assertThat(classRepository.count()).isEqualTo(0);
        Assertions.assertThat(studentRepository.count()).isEqualTo(0);
    }
}

總結(jié)

本示例中建立了雙向映射署驻，單向映射可以參考：Spring Boot JPA @ManyToOne 單向映射奋献；
本實(shí)例中使用了【表關(guān)聯(lián)】的表結(jié)構(gòu)設(shè)計策略，針對一對多和多對一的實(shí)體關(guān)系而言旺上，還可以使用【外鍵關(guān)聯(lián)】的表結(jié)構(gòu)設(shè)計策略瓶蚂。

Spring Boot JPA @OneToMany @ManyToOne 雙向映射

目錄

開發(fā)環(huán)境

基礎(chǔ)示例

總結(jié)