SpringBoot系列（七） jpa的使用，以增删改查为例

JPA是Java Persistence API的简称，Java持久层API，是JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。

它是SUN公司推出的一套基于ORM的规范。ORM又是什么？全英文名为Object-Relational Mapping：对象关系映射，简单来说为了不用JDBC那一套原始方法来操作数据库，ORM框架横空出世。

简单介绍下，Spring中的Spring-data-jpa技术，Spring Data JPA 是 Spring Data 系列的一部分，可以轻松实现基于 JPA 的存储库。该模块在处理对基于 JPA 的数据访问层的有所增强。使用数据访问技术快速构建应用变得更加容易。
特征：

支持基于spring和JPA构建存储数据业务
支持基于实体映射的XML
提供使用原生sql能力的@Query注解
分页支持、动态查询

本文的目录结构：

表示层：controller
业务层：Entity、Service、Vo
数据访问层：Repository

下面，我们通过一个完整地项目来展现JPA地能力：

1、创建数据库和表：

我们使用Navicat for MySQL工具，执行建表语句，创建一个student表

student建表语句

CREATE TABLE `student` (
  `student_id` varchar(50) NOT NULL,
  `name` varchar(50) NOT NULL DEFAULT 'cavan',
  `classroom` varchar(50) NOT NULL DEFAULT '0',
  `sex` varchar(10) NOT NULL DEFAULT '',
  `email` varchar(50) NOT NULL,
  `phone` varchar(20) NOT NULL DEFAULT '',
  `created_by` varchar(20) NOT NULL DEFAULT 'cavan',
  `last_modified_by` varchar(20) NOT NULL DEFAULT 'cavan',
  `last_modified_date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `created_date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`student_id`),
  UNIQUE KEY (`email`,`phone`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8mb4;

查看创建后的表：

2、引入依赖包

pom.xml的配置信息

pom.xml

        <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>

        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>4.1.14</version>
        </dependency>

3、配置application.properties连接数据库信息

application.properties

# 应用名称
spring.application.name=jpa
# 数据库驱动：
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
# 数据源名称
spring.datasource.name=defaultDataSource
# 数据库连接地址
spring.datasource.url=jdbc:mysql://121.43.225.17:3306/test?serverTimezone=UTC
# 数据库用户名&密码：
spring.datasource.username=root
spring.datasource.password=
# 应用服务 WEB 访问端口
server.port=8888

4、业务层

4.1 定义entity实体类（StudentEntity类）

StudentEntity类

package com.cavan.jpa.entity;

import org.hibernate.annotations.Generated;
import org.hibernate.annotations.GenerationTime;
import org.hibernate.annotations.GenericGenerator;

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

import java.sql.Timestamp;

/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-03 20:44
 */
@Entity
@Table(name = "student")
@GenericGenerator(name = "uuid", strategy = "uuid")
public class StudentEntity {
    private String id;
    private String name;
    private String classroom;
    private String sex;
    private String email;
    private String phone;
    private String createdBy;
    private String lastModifiedBy;
    private Timestamp lastModifiedDate;
    private Timestamp createdDate;

    @Id
    @GeneratedValue(generator = "uuid")
    @Column(name = "student_id")
    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getClassroom() {
        return classroom;
    }

    public void setClassroom(String classroom) {
        this.classroom = classroom;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(String createdBy) {
        this.createdBy = createdBy;
    }

    public String getLastModifiedBy() {
        return lastModifiedBy;
    }

    public void setLastModifiedBy(String lastModifiedBy) {
        this.lastModifiedBy = lastModifiedBy;
    }

    @Column(name = "last_modified_date",
            columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP",
            insertable = false,
            updatable = false)
    @Generated(GenerationTime.ALWAYS)
    public Timestamp getLastModifiedDate() {
        return lastModifiedDate;
    }

    public void setLastModifiedDate(Timestamp lastModifiedDate) {
        this.lastModifiedDate = lastModifiedDate;
    }

    @Column(name = "created_date",
            columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP",
            insertable = false,
            updatable = false)
    @Generated(GenerationTime.ALWAYS)
    public Timestamp getCreatedDate() {
        return createdDate;
    }

    public void setCreatedDate(Timestamp createdDate) {
        this.createdDate = createdDate;
    }
}

一些常用注解（本文用到不多）：

注解	作用	常用属性
@Entity	指定当前类是实体类
@Table	指定实体类和表之间的对应关系	name：指定数据库表的名称
@EntityListeners	在实体类增删改的时候监听，为创建人/创建时间等基础字段赋值	value：指定监听类
@Id	指定当前字段是主键
@SequenceGenerator	指定数据库序列别名	sequenceName：数据库序列名，name：取的别名
@GeneratedValue	指定主键的生成方式	strategy ：指定主键生成策略 generator：选择主键别名
@Column	指定实体类属性和数据库表之间的对应关系	name：指定数据库表的列名称， unique：是否唯一， nullable：是否可以为空，nserttable：是否可以插入，updateable：是否可以更新，columnDefinition: 定义建表时创建此列的DDL
@CreatedBy	自动插入创建人
@CreatedDate	自动插入创建时间
@LastModifiedBy	自动修改更新人
@LastModifiedDate	自动修改更新时间
@JsonFormat	插入/修改/读取的时间转换成想要的格式	pattern：展示格式，timezone：国际时间

注意：

有了@EntityListeners(AuditingEntityListener.class)这个注解，@CreatedBy、@CreatedDate 、@LastModifiedBy 、@LastModifiedDate才生效哦，而且创建人和更新人需要另作注入操作。

4.2 Vo请求/响应类

由于我们在进行增删改查操作时所需要的请求入参信息是不一样的，接口响应需要返回的信息也不太一样，所以我们定义了不同的请求类，用以接收请求消息，传递给业务使用。这里我们分别定义了StudentVo类（创建、更新使用）、StudentIdVo类（删除使用）、StudentQueryVo类（查询使用）。
实际上，当你严格校验你的请求参数时，创建和更新请求类应该创建两个类加以区分，这个在请求入参校验实践会详细讲解。
创建更新请求Vo类：

StudentVo类

package com.cavan.jpa.vo;

/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-03 22:02
 */
public class StudentVo {
    private String id;
    private String name;
    private String classroom;
    private String sex;
    private String email;
    private String phone;
    private String createdBy;
    private String lastModifiedBy;

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getClassroom() {
        return classroom;
    }

    public void setClassroom(String classroom) {
        this.classroom = classroom;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getCreatedBy() {
        return createdBy;
    }

    public void setCreatedBy(String createdBy) {
        this.createdBy = createdBy;
    }

    public String getLastModifiedBy() {
        return lastModifiedBy;
    }

    public void setLastModifiedBy(String lastModifiedBy) {
        this.lastModifiedBy = lastModifiedBy;
    }
}

删除请求类：

StudentIdVo类

package com.cavan.jpa.vo;

/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-04 11:55
 */
public class StudentIdVo {
    private String id;

    public String getId() {
        return id;
    }

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

查询请求类：

StudentQueryVo类

package com.cavan.jpa.vo;

/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-05 11:25
 */
public class StudentQueryVo {
    private Integer pagesize;
    private Integer pageNum;
    private String id;
    private String name;
    private String classroom;
    private String sex;

    public Integer getPagesize() {
        return pagesize;
    }

    public void setPagesize(Integer pagesize) {
        this.pagesize = pagesize;
    }

    public Integer getPageNum() {
        return pageNum;
    }

    public void setPageNum(Integer pageNum) {
        this.pageNum = pageNum;
    }

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getClassroom() {
        return classroom;
    }

    public void setClassroom(String classroom) {
        this.classroom = classroom;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
}

4.3 service服务类（分为 StudentService 服务接口类和 StudentServiceImpl 服务实现类）

业务逻辑层的核心就是service服务及其实现类，一些重要的逻辑都会写到impl中，而不是直接写在controller中。
我们对学生实现最简单的新增、删除、修改、查询功能。
代码如下：
服务接口类：

StudentService类

package com.cavan.jpa.service;

import com.cavan.jpa.entity.StudentEntity;
import com.cavan.jpa.vo.StudentIdVo;
import com.cavan.jpa.vo.StudentQueryVo;
import com.cavan.jpa.vo.StudentVo;

import java.util.List;

public interface StudentService {
    /**
     * create student
     *
     * @return student
     */
    String create(StudentVo studentVo);

    /**
     * delete student
     *
     * @return student
     */
    String delete(StudentIdVo studentIdVo);

    /**
     * update student
     *
     * @return student
     */
    String update(StudentVo studentVo);

    /**
     * query student
     *
     * @return student
     */
    List<StudentEntity> query(StudentQueryVo studentQueryVo);

}

服务实现类：

StudentServiceImpl类

package com.cavan.jpa.service.impl;

import cn.hutool.core.bean.BeanUtil;
import cn.hutool.core.bean.copier.CopyOptions;
import com.cavan.jpa.entity.StudentEntity;
import com.cavan.jpa.repository.StudentRepository;
import com.cavan.jpa.service.StudentService;
import com.cavan.jpa.vo.StudentIdVo;
import com.cavan.jpa.vo.StudentQueryVo;
import com.cavan.jpa.vo.StudentVo;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.ArrayList;
import java.util.List;


/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-03 21:37
 */
@Service
@Transactional(rollbackFor = Exception.class)
public class StudentServiceImpl implements StudentService {
    @Autowired
    private StudentRepository studentRepository;

    @Override
    public String create(StudentVo studentVo) {
        StudentEntity studentEntity = new StudentEntity();
        BeanUtils.copyProperties(studentVo, studentEntity);
        studentRepository.save(studentEntity);
        return "create ok";
    }

    @Override
    public String delete(StudentIdVo studentIdVo) {
        studentRepository.deleteById(studentIdVo.getId());
        return "delete ok";
    }

    @Override
    public String update(StudentVo studentVo) {
        StudentEntity studentEntity = studentRepository.findById(studentVo.getId()).get();
        BeanUtil.copyProperties(studentVo, studentEntity, true,
                CopyOptions.create().setIgnoreNullValue(true).setIgnoreError(true));
        studentRepository.save(studentEntity);
        return "update ok";
    }

    @Override
    public List<StudentEntity> query(StudentQueryVo studentQueryVo) {
        Integer pageNum = studentQueryVo.getPageNum();
        List<Sort.Order> orders = new ArrayList<>();
        orders.add(new Sort.Order(Sort.Direction.DESC, "last_modified_date"));
        Sort sort = Sort.by(orders);
        Pageable pageable = PageRequest.of(pageNum > 0 ? pageNum - 1 : pageNum, studentQueryVo.getPagesize(), sort);
        Page<StudentEntity> page = studentRepository.queryStudent(studentQueryVo.getId(),
                studentQueryVo.getName(),
                studentQueryVo.getSex(),
                studentQueryVo.getClassroom(), pageable);
        if (page.getTotalPages() < pageNum && page.getTotalPages() > 0) {
            page = studentRepository.queryStudent(studentQueryVo.getId(),
                    studentQueryVo.getName(),
                    studentQueryVo.getSex(),
                    studentQueryVo.getClassroom(), pageable);
        }
        return page.getContent();
    }
}

5、表示层

我们这里全部使用的是POST请求，分别定义了以下功能接口：

创建接口，用来创建一条学生信息数据
删除接口，根据学生的学号删除学生信息
更新接口，根据学生的学号更新学生信息
查询接口，根据学生姓名、性别、班级等进行查询操作

StudentManageController类

package com.cavan.jpa.controller;

import com.cavan.jpa.entity.StudentEntity;
import com.cavan.jpa.service.StudentService;
import com.cavan.jpa.vo.StudentIdVo;
import com.cavan.jpa.vo.StudentQueryVo;
import com.cavan.jpa.vo.StudentVo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * @program: jpa
 * @description: <description>
 * @author: cavan
 * @create: 2021-12-03 20:22
 */
@RestController
@RequestMapping("/student")
public class StudentManageController {
    @Autowired
    private StudentService service;

    /**
     * 创建学生
     *
     * @param studentVo 学生信息
     * @return create OK
     */
    @PostMapping("/create")
    public String create(@RequestBody StudentVo studentVo) {
        return service.create(studentVo);
    }

    /**
     * 根据学生的学号删除学生信息
     *
     * @param studentIdVo 学号
     * @return delete OK
     */
    @PostMapping("/delete")
    public String delete(@RequestBody StudentIdVo studentIdVo) {
        return service.delete(studentIdVo);
    }

    /**
     * 根据学生的学号更新学生信息
     *
     * @param studentVo 学号
     * @return update OK
     */
    @PostMapping("/update")
    public String update(@RequestBody StudentVo studentVo) {
        return service.update(studentVo);
    }

    /**
     * 根据学生姓名、性别、班级等查询
     *
     * @return query OK
     */
    @PostMapping("/query")
    public List<StudentEntity> query(@RequestBody StudentQueryVo studentQueryVo) {
        return service.query(studentQueryVo);
    }
}

6、数据连接层

这里只定义了原生sql的查询方法，其他基本的增删改查操作使用JPA内部提供的即可，只用继承 JpaRepository，不需要另外声明。

StudentRepository接口

package com.cavan.jpa.repository;

import com.cavan.jpa.entity.StudentEntity;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

@Repository
public interface StudentRepository extends JpaRepository<StudentEntity, String> {
    /**
     * query
     */
    @Query(value = "select * from student where IF(ifnull(?1,'')!='',student_id=?1,1=1) " +
            "and IF(ifnull(?2,'')!='',name like CONCAT('%',?2,'%'),1=1) " +
            "and IF(ifnull(?3,'')!='',sex like CONCAT('%',?3,'%'),1=1) " +
            "and IF(ifnull(?4,'')!='',classroom like CONCAT('%',?4,'%'),1=1)",
            countQuery = "select count(1) from student where IF(ifnull(?1,'')!='',student_id=?1,1=1) " +
                    "and IF(ifnull(?2,'')!='',name like CONCAT('%',?2,'%'),1=1) " +
                    "and IF(ifnull(?3,'')!='',sex like CONCAT('%',?3,'%'),1=1) " +
                    "and IF(ifnull(?4,'')!='',classroom like CONCAT('%',?4,'%'),1=1)", nativeQuery = true)
    Page<StudentEntity> queryStudent(String id, String name, String sex, String classroom, Pageable pageable);
}

问题记录：

（1）第一个问题
Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-12-03 22:42:34.389 ERROR 15628 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :

APPLICATION FAILED TO START

Description:

Field service in com.cavan.jpa.controller.StudentManageController required a bean of type 'com.cavan.jpa.service.StudentService' that could not be found.

The injection point has the following annotations:
- @org.springframework.beans.factory.annotation.Autowired(required=true)

Action:

Consider defining a bean of type 'com.cavan.jpa.service.StudentService' in your configuration.

问题分析：
此问题是由于我在使用注解时错误的将
@Service
@Transactional(rollbackFor = Exception.class)
这两个注解放在了StudentService接口类上，实际应该定义在实现类上。

（2）第二个问题
2021-12-03 23:10:39.864 ERROR 15240 --- [nio-8888-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper : Unknown column 'created_by' in 'field list'
2021-12-03 23:10:39.917 ERROR 15240 --- [nio-8888-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.InvalidDataAccessResourceUsageException: could not execute statement; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute statement] with root cause

java.sql.SQLSyntaxErrorException: Unknown column 'created_by' in 'field list'
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120) ~[mysql-connector-java-8.0.22.jar:8.0.22]

问题分析：
在使用建表语句时，我们创建的Entity实体类中的createdBy字段，映射到数据时会自动识别小驼峰，将其对应成created_by字段，所以建表时，我们要使用下划线方式，创建字段。
错误建表字段：

（3）第三个问题

2021-12-03 23:21:02.685 ERROR 14972 --- [nio-8888-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper : Column 'classroom' cannot be null
2021-12-03 23:21:02.744 ERROR 14972 --- [nio-8888-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement] with root cause

java.sql.SQLIntegrityConstraintViolationException: Column 'classroom' cannot be null
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:117) ~[mysql-connector-java-8.0.22.jar:8.0.22]

问题分析：
未在请求参数前加 @RequestBody 注解导致请求传过去的参数都为null值