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[增删改查] 最规范的 JPA 一对多/多对一 CRUD 示例

程序员文章站 2022-05-09 09:24:48
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一、前言

1、多对一，一对多，都是一样的，反过来了而已。

2、之前写过一篇不使用主外键关系的多表 CRUD：
[增删改查] 最简单的 JPA 一对多/多对一 CRUD 设计
虽可以帮助新手快速使用 JPA，但是这样是不严谨的，特别是记录的删除，有了主外键关系就不会让你随意删除了。

3、其实，规范使用 JPA，还是很简单的。

二、代码

代码以及放到 github 上了：https://github.com/larger5/SpringBootJPAOM.git

1、代码结构

[增删改查] 最规范的 JPA 一对多/多对一 CRUD 示例

2、entity

① 学生
package com.cun.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "t_student")
public class Student {

    @Id
    @GeneratedValue
    private Integer id;

    @Column(length = 100)
    private String name;

    @ManyToOne
    @JoinColumn(name="department_id") // 默认也为 department_id
    Department department;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    // JPA 必备
    public Student() {
        super();
    }

}
② 宿舍
package com.cun.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "t_department")
public class Department {

    @Id
    @GeneratedValue
    private Integer id;

    @Column(length = 100)
    private String name;

    // 必注、必应主表 Student 属性 Department department;但是造成了JSON 死循环
//  @OneToMany(mappedBy="department") 
//  private Set<Student> students=new HashSet<Student>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

//  public Set<Student> getStudents() {
//      return students;
//  }
//
//  public void setStudents(Set<Student> students) {
//      this.students = students;
//  }

    // JPA 必备
    public Department() {
        super();
    }

}

3、dao

① 学生
package com.cun.dao;

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;

import com.cun.entity.Student;

public interface StudentDao extends JpaRepository<Student, Integer> {

    @Query(value="select * from t_student where department_id=?1",nativeQuery=true)
    List<Student> getStudentsByDepartmentId(Integer id);
}
② 宿舍
package com.cun.dao;

import org.springframework.data.jpa.repository.JpaRepository;

import com.cun.entity.Department;

public interface DepartmentDao extends JpaRepository<Department, Integer>{

}

4、Controller

① 学生
package com.cun.controller;

import java.util.List;

import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.cun.dao.StudentDao;
import com.cun.entity.Student;

import springfox.documentation.swagger2.annotations.EnableSwagger2;

/**
 * 多表 CRUD 注意点：
 * ① Select：JPA findOne 会同时查询外键值对应表的记录的其他属性（优点）
 * ② Delete、Update、Insert 同单表 CRUD 
 * @author linhongcun
 *
 */
@RestController
@RequestMapping("/student")
@EnableSwagger2
public class StudentController {

    @Autowired
    private StudentDao studentDao;

    /**
     * 1、查
     * @param id
     * @return
     */
    @GetMapping("/get/{id}")
    public Student getStudentById(@PathVariable Integer id) {
        return studentDao.findOne(id);
    }

    /**
     * 2、增
     * @param student
     * @return
     */
    @PostMapping("/insert")
    public Student insertStudent(Student student) {
        studentDao.save(student);
        return student;
    }

    /**
     * 3、删
     * @param id
     * @return
     */
    @DeleteMapping("/delete/{id}")
    public Student deleteStudentById(@Valid @PathVariable Integer id, BindingResult bindingResult) {
        Student student = studentDao.findOne(id);
        studentDao.delete(id);
        return student;
    }

    /**
     * 4、改
     * @param student
     * @return
     */
    @PutMapping("/update")
    public Student updateStudent(Student student) {
        studentDao.save(student);
        return student;
    }

    /**
     * 5、全
     * @return
     */
    @GetMapping("/all")
    public List<Student> getAllStudents() {
        return studentDao.findAll();
    }
}
② 宿舍
package com.cun.controller;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.cun.dao.DepartmentDao;
import com.cun.dao.StudentDao;
import com.cun.entity.Department;
import com.cun.entity.Student;

import springfox.documentation.swagger2.annotations.EnableSwagger2;

/**
 * 多表 CRUD 注意点：
 * ① Delete：宿舍的一条记录id作为学生外键属性值时不能删除
 * ② Insert、Update、Select 同单表 CRUD
 * @author linhongcun
 *
 */
@RestController
@RequestMapping("/department")
@EnableSwagger2
public class DepartmentController {

    @Autowired
    private DepartmentDao departmentDao;

    @Autowired
    private StudentDao studentDao; // 删除检查是否存在关系

    /**
     * 1、查
     * @param id
     * @return
     */
    @GetMapping("/get/{id}")
    public Department getDepartmentById(@PathVariable Integer id) {
        return departmentDao.findOne(id);
    }

    /**
     * 2、删：这个要特别注意，其他的没什么好讲的
     * @param id
     * @return
     */
    @DeleteMapping("/delete/{id}")
    public Map<String, Object> deleteDeparmentById(@PathVariable Integer id) {
        Department department = departmentDao.findOne(id);
        Map<String, Object> map = new HashMap<String, Object>();
        List<Student> studentsByDepartmentId = studentDao.getStudentsByDepartmentId(id);
        if (studentsByDepartmentId.size() == 0) {
            departmentDao.delete(id);
            map.put("status", true);
            map.put("msg", "删除成功");
            map.put("data", department);
        } else {
            map.put("status", false);
            map.put("msg", "不能删除，因存在关联关系");
        }
        return map;
    }

    /**
     * 3、改
     * @param department
     * @return
     */
    @PutMapping("/update")
    public Department updateDepartment(Department department) {
        departmentDao.save(department);
        return department;
    }

    /**
     * 4、增
     * @param department
     * @return
     */
    @PostMapping("/insert")
    public Department insertDepartment(Department department) {
        departmentDao.save(department);
        return department;
    }

    /**
     * 5、全
     * @return
     */
    @GetMapping("/all")
    public List<Department> getAllDepartments() {
        return departmentDao.findAll();
    }

}

5、yml

server:
  port: 80 #为了以后访问项目不用写端口号
  context-path: / #为了以后访问项目不用写项目名
spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/springboot?useUnicode=true&characterEncoding=utf-8  #解决中文乱码的问题
    username: root
    password: 123
  jpa: 
    hibernate:
      ddl-auto: update  #数据库同步代码
    show-sql: true      #dao操作时，显示sql语句

6、pom

① Swagger 接口（可选）
        <!-- swagger生成接口API -->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>2.7.0</version>
        </dependency>

        <!-- 接口API生成html文档 -->
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>2.6.1</version>
        </dependency>
② JPA、MySQL、Web
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

三、其他

1、Swagger 测试接口

[增删改查] 最规范的 JPA 一对多/多对一 CRUD 示例

2、数据库自动生成主外键关系

[增删改查] 最规范的 JPA 一对多/多对一 CRUD 示例

3、JPA 单表 CRUD 的例子

[增删改查] SpringBoot+JPA+EasyUI+MySQL 基本 CURD

相关标签： jpa 多表

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