SpringBoot 中JPA集成PostgreSql(详细步骤)

什么是JPA？（Java Persistence API）

Spring Data JPA, part of the larger Spring Data family, makes it easy to easily implement JPA based repositories. This module deals with enhanced support for JPA based data access layers. It makes it easier to build Spring-powered applications that use data access technologies.

Implementing a data access layer of an application has been cumbersome for quite a while. Too much boilerplate code has to be written to execute simple queries as well as perform pagination, and auditing. Spring Data JPA aims to significantly improve the implementation of data access layers by reducing the effort to the amount that’s actually needed. As a developer you write your repository interfaces, including custom finder methods, and Spring will provide the implementation automatically.

Features

Sophisticated support to build repositories based on Spring and JPA
Support for Querydsl predicates and thus type-safe JPA queries
Transparent auditing of domain class
Pagination support, dynamic query execution, ability to integrate custom data access code
Validation of @Query annotated queries at bootstrap time- Support for XML based entity mapping- JavaConfig based repository configuration by introducing @EnableJpaRepositories.

国内说法

JPA 是指 Java Persistence API，即 Java 的持久化规范，一开始是作为 JSR-220 的一部分。 JPA 的提出，主要是为了简化 Java EE 和 Java SE 应用开发工作，统一当时的一些不同的 ORM 技术。一般来说，规范只是定义了一套运作的规则，也就是接口，而像我们所熟知的Hibernate 则是 JPA 的一个实现(Provider)。

JPA 定义了什么，大致有：

ORM 映射元数据，用来将对象与表、字段关联起来- 操作API，即完成增删改查的一套接口- JPQL 查询语言，实现一套可移植的面向对象查询表达式

PostgreSQL简介

PostGreSQL是一个功能强大的开源对象关系数据库管理系统(ORDBMS)，号称世界上最先进的开源关系型数据库 经过长达15年以上的积极开发和不断改进，PostGreSQL已在可靠性、稳定性、数据一致性等获得了很大的提升。对比时下最流行的 MySQL 来说，PostGreSQL 拥有更灵活，更高度兼容标准的一些特性。此外，PostGreSQL基于MIT开源协议，其开放性极高，这也是其成为各个云计算大T 主要的RDS数据库的根本原因。

JPA中使用PostgreSQL

一、添加依赖包

Spring Boot Mavn项目 Pom.xml文件中添加依赖包

<!--jpa与postgresql-->
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency><groupId>org.postgresql</groupId><artifactId>postgresql</artifactId><scope>runtime</scope>
</dependency>

二、配置PostgreSQL和jpa

在application-dev.yml（开发环境）中添加如下：

server:port: 8088
spring:datasource:type: com.zaxxer.hikari.HikariDataSourcedriver-class-name: org.postgresql.Driverurl: jdbc:postgresql://192.168.0.30:5432/thingsboardusername: rootpassword: 123456hikari:minimum-idle: 5maximum-pool-size: 15auto-commit: trueidle-timeout: 30000connection-timeout: 60000validation-timeout: 10000jpa:show-sql: trueredis:host: 127.0.0.1database: 0port: 6379password:lettuce:pool:max-active: 10max-idle: 10max-wait: 5ms
tb:url: https://nybx-ljyz.cpic.com.cn/aimslogging:level: debuglevel.top: debug

注意：

yourdatabase,yourusername,yourpassword等信息是否配置正确。
spring.jpa.hibernate.ddl-auto 指定为 update，这样框架会自动帮我们创建或更新表结构

三、定义Entity

package com.zlzk.video.server.entity;import lombok.Data;import javax.persistence.*;@Data
@Entity
//@Table(name = "attribute_kv")
public class Attribute {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Integer rownum;private String entity_type;private String entity_id;private String attribute_type;private String attribute_key;private Boolean bool_v;private String str_v;private Long long_v;private Float dbl_v;/*** Type=json*/private String json_v;private Long last_update_ts;
}

注意：

避坑！ 若使用自定义sql，且用自定义实体类（即查出什么字段，实体类就有什么变量）来接收，如果查出来的字段没有一个字段是唯一的（jpa要求有一个唯一的字段），查询出的数据会抽风，参考链接

解决思路：提供一个唯一字段即可，这里是用的rownum，不同数据库可用row_num、row_id等，比如我用的PostgreSQL，则是需要加row_number() OVER () AS row_num ,并在实体类加上row_num变量来接收查询结果，实际执行sql如下：
```
select  row_number() OVER (ORDER BY entity_id) as rownum, * from attribute_kv where entity_id = '1eaaee56e9abd40933ce332a36104a6'
```
避坑！简单类型的数据不能被设置为null，比如数据库中float8，需设置为Float，否则可能报错错误org.hibernate.PropertyAccessException: Null value was assigned to a property of…
如果你的数据库中有自己创建的嵌套schema,要在Table属性中进行写明，如@Table(name = “bookshelf”,schema = “yourschema”)
bookName这样的写法会导致如果数据库没有这个数据元，则会创建成book_name

四、定义dao

package com.zlzk.video.server.dao;import com.zlzk.video.server.entity.Attribute;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
/*** Param注解*/
import java.util.List;public interface AttributeDao extends JpaRepository<Attribute,String> {//Attribute findAttriById(String entity_id);@Query(name = "findById",nativeQuery = true,value ="select  row_number() OVER (ORDER BY entity_id) as rownum, * from attribute_kv where entity_id = :entity_id")List<Attribute> findByEntity_id(@Param("entity_id")String entity_id);
}

注意：

如果**@Query中有*号**，要在尾部加上nativeQuery = true
更规范的写法应该是写repository包下

五、定义service

package com.zlzk.video.server.service.attribute;import com.zlzk.video.server.dao.AttributeDao;
import com.zlzk.video.server.entity.Attribute;
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.stereotype.Service;import java.util.List;@Service
public class AttributeServiceIml implements AttributeService {@Autowiredprivate AttributeDao attributeDao;/*@Overridepublic Attribute findById(String entity_id) {return attributeDao.findAttriById(entity_id);}*/@Overridepublic void delete(String entity_id) {attributeDao.deleteById(entity_id);}@Overridepublic Attribute save(Attribute attribute) {return  attributeDao.save(attribute);}@Overridepublic Page<Attribute> findAll(int page, int pagesize) {Pageable pageable = PageRequest.of(page,pagesize);return attributeDao.findAll(pageable);}@Overridepublic Attribute update(Attribute attribute) {return attributeDao.save(attribute);}@Overridepublic List<Attribute> findByEntity_id(String entity_id) {return attributeDao.findByEntity_id(entity_id);}
}

六、定义controller

package com.zlzk.video.server.controller.attribute;import com.zlzk.video.server.entity.Attribute;
import com.zlzk.video.server.service.attribute.AttributeService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.web.bind.annotation.*;import javax.servlet.http.HttpServletResponse;
import java.util.List;@RestController
@RequestMapping("/attr")
public class AttributeController {@Autowiredprivate AttributeService attributeService;@PostMapping("/reg")public Attribute reg(Attribute Attribute){return  attributeService.save(Attribute);}@GetMapping("/findAll")public Page<Attribute> findAll(Integer page, HttpServletResponse response){response.setHeader("Access-Control-Allow-Origin","*");if(page==null||page<=0){page = 0;}else {page -= 1;}return  attributeService.findAll(page,5);}@GetMapping("/delete/{entity_id}")public String delete(@PathVariable String entity_id){attributeService.delete(entity_id);return "sucesss";}/**** @param Attribute* @return*/@PostMapping("/update")public Attribute update(Attribute Attribute){return attributeService.save(Attribute);}/*@GetMapping("/select/{id}")public  Attribute select(@PathVariable String entity_id)throws Exception{return attributeService.findById(entity_id);}*/@GetMapping("/findByEntity_id/{entity_id}")public List<Attribute> findByName(@PathVariable String entity_id){return attributeService.findByEntity_id(entity_id);}}

注意：

JWT鉴权中放开

.pathMatchers("/attr/findByEntity_id/**").permitAll()

本人测试结果如下(通过entity_id找数据):

[{"rownum": 1,"entity_type": "DEVICE","entity_id": "1eaaee56e9abd40933ce332a36104a6","attribute_type": "CLIENT_SCOPE","attribute_key": "battery","bool_v": null,"str_v": null,"long_v": 1,"dbl_v": null,"json_v": null,"last_update_ts": 1592377103023
}, {"rownum": 2,"entity_type": "DEVICE","entity_id": "1eaaee56e9abd40933ce332a36104a6","attribute_type": "CLIENT_SCOPE","attribute_key": "latestMoveTime","bool_v": null,"str_v": null,"long_v": 1592211412899,"dbl_v": null,"json_v": null,"last_update_ts": 1592211502537
}, {"rownum": 3,"entity_type": "DEVICE","entity_id": "1eaaee56e9abd40933ce332a36104a6","attribute_type": "CLIENT_SCOPE","attribute_key": "latitude","bool_v": null,"str_v": null,"long_v": 1,"dbl_v": null,"json_v": null,"last_update_ts": 1592377103023
}, {"rownum": 4,"entity_type": "DEVICE","entity_id": "1eaaee56e9abd40933ce332a36104a6","attribute_type": "CLIENT_SCOPE","attribute_key": "limitAlarmPeriod","bool_v": null,"str_v": null,"long_v": 10,"dbl_v": null,"json_v": null,"last_update_ts": 1592211502537
}, {"rownum": 5,"entity_type": "DEVICE","entity_id": "1eaaee56e9abd40933ce332a36104a6","attribute_type": "CLIENT_SCOPE","attribute_key": "longitude","bool_v": null,"str_v": null,"long_v": 1,"dbl_v": null,"json_v": null,"last_update_ts": 1592377103023
}