springboot使用Spring Data JPA

新建SpringBoot项目

POM.xml

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-data-jpa</artifactId>
      <version>2.6.3</version>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
      <version>2.6.3</version>
    </dependency>

    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <scope>5.7.0</scope>
    </dependency>

application.properties配置

spring.datasource.url=jdbc:mysql://localhost:3306/dbjpa?serverTimezone=UTC&characterEncoding=utf8
spring.datasource.username=root
spring.datasource.password=root

#配置JPA
##使用Mysql5.7数据库,写MySQL5Dialect的话默认使用myisam引擎,MySQL5InnoDBDialect会使用innodb引擎
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect
##update表示当实体类有任何变化时会更新Mysql数据库字段
##create和update都只能用在开发环境,线上环境一定要用none
spring.jpa.hibernate.ddl-auto=update
##打印sql
spring.jpa.show-sql=true

编写代码

@Entity说明这个class是实体类，并且使用默认的orm规则，即class名即数据库表中表名，class字段名即表中的字段名.

@Table来改变class名与数据库中表名的映射规则.

@Column来改变class中字段名与数据库中表的字段名的映射规则.

package com.autumn.model;

import javax.persistence.*;

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

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(nullable = false,name = "name")
    private String name;
}

运行代码生成库表

在代码运行之前要先新建数据库

启动springboot项目，自动新建表

DAO接口

新建StudentDao数据库操作接口，继承CrudRepository接口。

import com.autumn.model.Student;
import org.springframework.data.repository.CrudRepository;

/**
 * 继承spring data jpa的CrudRepository<类,类的主键类型>
 **/
public interface StudentDao extends CrudRepository<Student,Long>{

}

Service类

service直接调用StudentDao的接口CrudRepository的方法。

import com.autumn.dao.StudentDao;
import com.autumn.exceptions.StudentEmptyNameException;
import com.autumn.exceptions.StudentNonExistException;
import com.autumn.model.Student;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class StudentService {
    @Autowired
    private StudentDao dao;

    /*添加*/
    public Student add(Student student){
        if (student.getName().isEmpty()){
            throw new StudentEmptyNameException("学生姓名为空!");
        }
        return dao.save(student);
    }

    /*修改*/
    public Student update(Student student){
        if (student.getId()==null || dao.existsById(student.getId())){
            throw new StudentNonExistException("学生无ID");
        }
        return dao.save(student);
    }

    /*查询所有*/
    public List<Student> getAllStudents(){
        return (List<Student>) dao.findAll();
    }

    /*根据id获取详细信息*/
    public Optional<Student> getStudentById(Long id){
        return dao.findById(id);
    }

}

Controller层

@RestController
@RequestMapping("api/student")
public class StudentController {
    @Autowired
    private StudentService service;

    /*查询所有学生*/
    @GetMapping
    public List<Student> getAllStudents(){
        return service.getAllStudents();
    }

    /*注册学生信息*/
    @PostMapping
    @RequestMapping("register")
    public ResponseEntity<String> register(@RequestBody Student student){
        try {
            service.add(student);
            return ResponseEntity.ok("注册学生信息" + student.toString());
        }catch (StudentEmptyNameException e){
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
        }
    }
}

一对多业务添加

新增UniversityClass班级业务

model类

import com.fasterxml.jackson.annotation.JsonIgnore;
import javax.persistence.*;
import java.util.List;

@Entity
@Table(name = "university_class")
public class UniversityClass {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column(nullable = false)
    Integer year;

    @Column(nullable = false)
    Integer number;

    @OneToMany(mappedBy = "universityClass")
    List<Student> students;

    public Long getId() {
        return id;
    }

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

    public Integer getYear() {
        return year;
    }

    public void setYear(Integer year) {
        this.year = year;
    }

    public Integer getNumber() {
        return number;
    }

    public void setNumber(Integer number) {
        this.number = number;
    }
    //转换为json是忽略此字段,不然会无限递归
    @JsonIgnore
    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "UniversityClass{" +
                "id=" + id +
                ", year=" + year +
                ", number=" + number +
                '}';
    }
}

Dao层

package com.autumn.dao;

import com.autumn.model.UniversityClass;
import org.springframework.data.repository.CrudRepository;

public interface UniversityClassDao extends CrudRepository<UniversityClass,Long>{
}

Service层

package com.autumn.service;

import com.autumn.dao.UniversityClassDao;
import com.autumn.exceptions.InvalidUniversityClassException;
import com.autumn.model.UniversityClass;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.Calendar;
import java.util.List;

@Service
public class UniversityClassService {

    @Autowired
    UniversityClassDao dao;

    /*查询所有*/
    public List<UniversityClass> getAll() {
        return (List<UniversityClass>) dao.findAll();
    }

    /*添加*/
    public UniversityClass add(UniversityClass universityClass){
        int currentYear = Calendar.getInstance().get(Calendar.YEAR);
        if(universityClass.getYear()<currentYear){
            throw new InvalidUniversityClassException("Cannot add class in the past!");
        }
        if(universityClass.getYear()>currentYear){
            throw new InvalidUniversityClassException("Cannot add class in the future!");
        }
        return dao.save(universityClass);
    }

}

Controller层

package com.autumn.controller;

import com.autumn.exceptions.InvalidUniversityClassException;
import com.autumn.model.UniversityClass;
import com.autumn.service.UniversityClassService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("api/class")
public class UniversityClassController {
    @Autowired
    private UniversityClassService service;

    /*查询所有*/
    @GetMapping
    public List<UniversityClass> getAllStudents(){
        return service.getAll();
    }

    /*添加*/
    @PostMapping
    @RequestMapping("add")
    public ResponseEntity<String> add(@RequestBody UniversityClass universityClass){
        try {
            UniversityClass savedUniversityClass = service.add(universityClass);
            return ResponseEntity.ok("添加班级信息: " + savedUniversityClass.toString());
        }catch (InvalidUniversityClassException e){
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
        }
    }
}

修改Student业务类

在Student的model类中添加字段

@ManyToOne
    @JoinColumn(name = "university_class_id")
    private UniversityClass universityClass;

在Student的service层中添加

@Autowired
    private UniversityClassDao universityClassDao;

    /**
     * 给学生分配班级
     * */
    public Student assignClass(Long studentId,Long classId){
        if (!dao.existsById(studentId)){
            throw new StudentNonExistException("Cannot find student Id"+studentId);
        }
        if(!universityClassDao.existsById(classId)){
            throw new StudentNonExistException("Cannot find calss Id"+studentId);
        }
        Student student = getStudentById(studentId).get();
        UniversityClass universityClass = universityClassDao.findById(classId).get();
        student.setUniversityClass(universityClass);
        return dao.save(student);
    }

在Student的Controller层中添加

/**
     * 给学生分配班级
     * @param studentId
     * @param classId
     * @return
     */
    @PostMapping(path = "assignclass/{sid}/{cid}")
    public ResponseEntity<String> assignClass2(@PathVariable("sid") Long studentId,@PathVariable("cid") Long classId){
        try{
            Student updatedstudent = service.assignClass(studentId, classId);
            return ResponseEntity.ok("Assigned class. "+updatedstudent.toString());
        }catch (StudentNonExistException e){
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
        }catch(InvalidUniversityClassException e){
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
        }
    }

给学生分配班级

查询所有学生

源码地址:

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