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Springboot 之使用 Spring data JPA

因为自己一直使用的是MyBatis,所以尝试了一下JPA。

关于spring data JPA

  • JPA 是Java 5 引入的一个标准。
  • Spring data JPA 是Spring对JPA标准的实现，实际上使用的是Hibernate。
  • Spring data JPA封装好了一些API让开发者按照标准编写一些类直接继承这些API并使用它们。
  • 开发者在调用这些API的时候，Spring会根据API名称和参数动态生成SQL交给ORM框架Hibernate去执行SQL并完成结果的封装

我个人觉得公司的项目可以考虑使用Spring data JPA，毕竟支持快速开发，还可以缩短开发周期。但是个人学习的时候，建议使用MyBatis这种半自动的ORM。毕竟你学会了Spring data JPA 只是学会了Spring data JPA。你学会使用MyBatis的时候，SQL也学会了。

Spring data JPA 的优缺点

  • 优点
    • 快速开发，减少了大量的SQL编写
    • 可以满足大部分单表操作和简单联查
  • 缺点
    • 由于是一些通用sql，遇到一些特定的业务需求就显得很笨，还不如直接手写sql

简单使用

新建一个springboot项目

我使用的是OpenJDK 11
选择spring data jpa, lombok, mysql-connector

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
    </dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

准备数据

新建两个表，一个是学生信息表，一个是学生成绩表，通过id逻辑关联

CREATE DATABASE /*!32312 IF NOT EXISTS*/ `test` /*!40100 DEFAULT CHARACTER SET utf8mb4 */;
USE `test`;
DROP TABLE IF EXISTS `t_student`;
CREATE TABLE `t_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'primary key',
  `created_time` datetime DEFAULT NULL COMMENT 'created time',
  `updated_time` datetime DEFAULT NULL COMMENT 'updated time',
  `name` varchar(20) DEFAULT NULL COMMENT '姓名',
  `birthday` date DEFAULT NULL COMMENT '生日',
  `address` varchar(200) DEFAULT NULL COMMENT '家庭住址',
  `phone` varchar(20) DEFAULT NULL COMMENT '联系方式',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COMMENT='学生信息表';


DROP TABLE IF EXISTS `t_student_score`;
CREATE TABLE `t_student_score` (
  `id` int(11) NOT NULL COMMENT 'primary key',
  `created_time` datetime DEFAULT NULL COMMENT 'created tiem',
  `updated_time` datetime DEFAULT NULL COMMENT 'updated tiem',
  `math` double DEFAULT '0' COMMENT '数学',
  `english` double DEFAULT '0' COMMENT '英语',
  `yuwen` double DEFAULT '0' COMMENT '语文',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 COMMENT='学生成绩表';

INSERT INTO `t_student` (`id`,`created_time`,`updated_time`,`name`,`birthday`,`address`,`phone`) 
VALUES (1,'2020-11-03 11:43:06','2020-11-03 11:43:06','张三','2001-01-01','江西赣州','188888888'),
(2,'2020-11-03 11:43:06','2020-11-03 11:43:06','李四','2000-05-01','广东韶关','177888888'),
(3,'2020-11-03 11:43:06','2020-11-03 11:43:06','王老五','2002-03-01','江苏南京','199888888'),
(4,'2020-11-03 11:43:06','2020-11-03 11:43:06','葛二蛋','2000-12-01','四川成都','166888888');

INSERT INTO `t_student_score` (`id`,`created_time`,`updated_time`,`math`,`english`,`yuwen`) VALUES 
(1,'2020-11-03 14:08:52','2020-11-03 14:08:52',93,24.5,85),
(2,'2020-11-03 14:08:52','2020-11-03 14:08:52',85,67.5,82),
(3,'2020-11-03 14:08:52','2020-11-03 14:08:52',22.5,93.5,70),
(4,'2020-11-03 14:08:52','2020-11-03 14:08:52',88,76.5,65);

项目结构

我使用的是VS Code.
image.png

代码

配置文件 application.yml

spring:
  jpa:
    properties:
      hibernate:
        enable_lazy_load_no_trans: true    # 解决 getOne 报错问题
  datasource:
    url: jdbc:mysql://localhost:3306/test?characterEncoding=utf-8
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: root
    password: password
    hikari:
    minimumIdle: 5
    maximumPoolSize: 15
    max-lifetime: 60000

Entity

  • Student
package com.yeyeck.springdatajpa.entity;

import java.time.LocalDate;
import java.time.LocalDateTime;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

import lombok.Data;


@Data
@Table(name = "t_student")
@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private LocalDateTime createdTime;
    private LocalDateTime updatedTime;
    private String name;
    private String address;
    private LocalDate birthday;
    private String phone;

    @OneToOne
    @JoinColumn(name="id", referencedColumnName = "id")
    private Score score;
}
  • Score
package com.yeyeck.springdatajpa.entity;

import java.time.LocalDateTime;

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

import lombok.Data;

@Entity
@Table(name = "t_student_score")
@Data
public class Score {
    @Id
    private Integer id;
    private Double math;
    private Double yuwen;
    private Double english;
    private LocalDateTime createdTime;
    private LocalDateTime updatedTime;
    
}

Repository

这个就比较简单了，大部分方法是调用父接口的方法。Repository<T, ID>主要有四种依次为父子关系

  • Repository<T, ID>：纯粹的接口声明，没有一个方法
  • CrudRepository<T, ID>：简单的CRUD
  • PagingAndSortingRepository<T, ID>: 实现分页
  • JpaRepository<T, ID>：继承了两个接口PagingAndSortingRepository和QueryByExampleExecutor
  • QueryByExampleExecutor：实现通过定制Example进行查询，我看了一下Example,应该是一些比较繁琐的查询sql主要的承担者
package com.yeyeck.springdatajpa.repository;

import java.time.LocalDate;
import java.util.List;

import com.yeyeck.springdatajpa.entity.Student;

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

@Repository
public interface StudentRepository extends JpaRepository<Student, Integer> {
    List<Student> findByBirthdayBetween(LocalDate of, LocalDate of2);
}

单元测试

package com.yeyeck.springdatajpa.repository;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.util.List;

import com.yeyeck.springdatajpa.entity.Student;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.domain.Sort;

import lombok.extern.slf4j.Slf4j;

@SpringBootTest
@Slf4j
public class StudentRepositoryTest {

    @Autowired
    StudentRepository studentRepository;

    @Test
    public void findAll() {
        List<Student> students = studentRepository.findAll();
        log.info(students.toString());
    }

    @Test
    public void findAllAndSort() {
        List<Student> students = studentRepository.findAll(Sort.by("birthday").descending());
        log.info(students.toString());
    }

    @Test
    public void findAllByIds() {
        List<Student> students = studentRepository.findAllById(List.of(1,3,4));
        log.info(students.toString());
    }

    @Test
    public void findById() {
        Student student = studentRepository.findById(1).get();
        log.info(student.toString());
    }

    @Test
    public void getOne() {
        Student student = studentRepository.getOne(1);
        log.info(student.toString());
    }

    @Test
    public void save() {
        Student student = new Student();
        student.setName("赵四");
        student.setPhone("166666666");
        student.setAddress("新疆乌鲁木齐");
        student.setBirthday(LocalDate.of(2000, 3, 1));
        student.setCreatedTime(LocalDateTime.now());
        student.setUpdatedTime(LocalDateTime.now());
        studentRepository.save(student);
        log.info(student.toString());
        // Student(id=5, createdTime=2020-11-03T16:15:30.662052800, updatedTime=2020-11-03T16:15:30.662052800, name=赵四, address=新疆乌鲁木齐, birthday=2000-03-01, phone=166666666, score=null)
    }

    @Test
    public void findByBirthdayBetween() {
        List<Student> students = studentRepository.findByBirthdayBetween(LocalDate.of(2001, 1, 1), LocalDate.of(2002, 5, 1));
        students.forEach(student -> log.info(student.toString()));
    }
    
}
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updated@2020-11-04
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