200103-SpringBoot系列JPA错误姿势之Entity映射

文章目录
  1. I. 映射问题
    1. 1. 项目基本配置
    2. 2. 错误case
    3. 3. 正确姿势一
    4. 4. 正确姿势二
  2. II. 其他
    1. 0. 项目&关联博文
    2. 1. 一灰灰Blog

本篇为JPA错误使用姿势第二篇,java的POJO类与数据库表结构的映射关系,除了驼峰命名映射为下划线之外,还会有什么别的坑么?

I. 映射问题

1. 项目基本配置

首先搭建基本的springboot + jpa项目, 我们使用的springboot版本为2.2.1.RELEASE,mysql版本5+

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<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>

项目配置文件application.properties

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## DataSource
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/story?useUnicode=true&characterEncoding=UTF-8&useSSL=false
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=
spring.jpa.database=MYSQL
spring.jpa.hibernate.ddl-auto=none
spring.jpa.show-sql=true
spring.jackson.serialization.indent_output=true
spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl

表结构

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CREATE TABLE `meta_group` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`group` varchar(32) NOT NULL DEFAULT '' COMMENT '分组',
`profile` varchar(32) NOT NULL DEFAULT '' COMMENT 'profile 目前用在应用环境 取值 dev/test/pro',
`desc` varchar(64) NOT NULL DEFAULT '' COMMENT '解释说明',
`deleted` int(4) NOT NULL DEFAULT '0' COMMENT '0表示有效 1表示无效',
`create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
`update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间',
PRIMARY KEY (`id`),
KEY `group_profile` (`group`,`profile`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COMMENT='业务配置分组表';

2. 错误case

java变量命名推荐的是驼峰命名方式,因此与数据库中字段的下划线方式需要关联映射,通过jpa的相关知识学习,我们知道可以使用@Column注解来处理,所以有下面这种写法

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@Data
@Entity
@Table(name = "meta_group")
public class ErrorMetaGroupPo {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;

@Column(name = "group")
private String group;

@Column(name = "profile")
private String profile;

@Column(name = "desc")
private String desc;

@Column(name = "deleted")
private Integer deleted;

@Column(name = "create_time")
private Timestamp createTime;

@Column(name = "update_time")
private Timestamp updateTime;
}

从命名上就可以看出上面这种case是错误的,那么到底是什么问题呢?

先写一个对应的Repository来实测一下

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public interface ErrorGroupJPARepository extends JpaRepository<ErrorMetaGroupPo, Integer> {
}

测试代码

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@Component
public class GroupManager {
@Autowired
private ErrorGroupJPARepository errorGroupJPARepository;

public void test() {
String group = UUID.randomUUID().toString().substring(0, 4);
String profile = "dev";
String desc = "测试jpa异常case!";
try {
int id = addGroup1(group, profile, desc);
System.out.println("add1: " + id);
} catch (Exception e) {
e.printStackTrace();
}
}

public Integer addGroup1(String group, String profile, String desc) {
ErrorMetaGroupPo jpa = new ErrorMetaGroupPo();
jpa.setGroup("add1: " + group);
jpa.setDesc(desc);
jpa.setProfile(profile);
jpa.setDeleted(0);
Timestamp timestamp = Timestamp.from(Instant.now());
jpa.setCreateTime(timestamp);
jpa.setUpdateTime(timestamp);
ErrorMetaGroupPo res = errorGroupJPARepository.save(jpa);
return res.getId();
}
}

从输出结果来看,提示的是sql异常,why?

  • group,desc 为关键字,拼sql的时候需要用反引号包裹起来

3. 正确姿势一

第一种正确使用姿势,直接在@column的name中,添加反引号包裹起来

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@Data
@Entity
@Table(name = "meta_group")
public class MetaGroupPO {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;

@Column(name = "`group`")
private String group;

@Column(name = "`profile`")
private String profile;

@Column(name = "`desc`")
private String desc;

@Column(name = "`deleted`")
private Integer deleted;

@Column(name = "`create_time`")
private Timestamp createTime;

@Column(name = "`update_time`")
private Timestamp updateTime;
}

4. 正确姿势二

除了上面的case之外,还有另外一种通用的方式,实现自定义的PhysicalNamingStrategy,实现字段映射

比如我们自定义JpaNamingStrategyStandardImpl继承自默认的PhysicalNamingStrategyStandardImpl策略,然后在字段名中,对于没有引号的包裹的字段名主动添加一个反引号

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public class JpaNamingStrategyStandardImpl extends PhysicalNamingStrategyStandardImpl {
@Setter
private static int mode = 0;

@Override
public Identifier toPhysicalColumnName(Identifier name, JdbcEnvironment context) {
if (mode == 1) {
if (name.isQuoted()) {
return name;
} else {
return Identifier.toIdentifier("`" + name.getText() + "`", true);
}
} else {
return name;
}
}
}

注意使用上面的映射策略,需要修改配置文件(application.properties)

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spring.jpa.hibernate.naming.physical-strategy=com.git.hui.boot.jpacase.strategy.JpaNamingStrategyStandardImpl

测试case

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@SpringBootApplication
public class Application {
public Application(GroupManager groupManager) {
groupManager.test();
}

public static void main(String[] args) {
JpaNamingStrategyStandardImpl.setMode(1);
SpringApplication.run(Application.class, args);
}
}

@Component
public class GroupManager {
@Autowired
private ErrorGroupJPARepository errorGroupJPARepository;

@Autowired
private GroupJPARepository groupJPARepository;


public void test() {
String group = UUID.randomUUID().toString().substring(0, 4);
String profile = "dev";
String desc = "测试jpa异常case!";
try {
int id = addGroup1(group, profile, desc);
System.out.println("add1: " + errorGroupJPARepository.findById(id));
} catch (Exception e) {
e.printStackTrace();
}

try {
int id2 = addGroup2(group, profile, desc);
System.out.println("add2: " + groupJPARepository.findById(id2));
} catch (Exception e) {
e.printStackTrace();
}
}

public Integer addGroup1(String group, String profile, String desc) {
ErrorMetaGroupPo jpa = new ErrorMetaGroupPo();
jpa.setGroup("add1: " + group);
jpa.setDesc(desc);
jpa.setProfile(profile);
jpa.setDeleted(0);
Timestamp timestamp = Timestamp.from(Instant.now());
jpa.setCreateTime(timestamp);
jpa.setUpdateTime(timestamp);
ErrorMetaGroupPo res = errorGroupJPARepository.save(jpa);
return res.getId();
}

public Integer addGroup2(String group, String profile, String desc) {
MetaGroupPO jpa = new MetaGroupPO();
jpa.setGroup("add2: " + group);
jpa.setDesc(desc);
jpa.setProfile(profile);
jpa.setDeleted(0);
Timestamp timestamp = Timestamp.from(Instant.now());
jpa.setCreateTime(timestamp);
jpa.setUpdateTime(timestamp);
MetaGroupPO res = groupJPARepository.save(jpa);
return res.getId();
}
}

执行之后输出:

II. 其他

0. 项目&关联博文

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