SpringBoot 系列 JPA 错误姿势之 Entity 映射
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+
org.springframework.boot
spring-boot-starter-data-jpa
mysql
mysql-connector-java
项目配置文件application.properties
## 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
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
@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
public interface ErrorGroupJPARepository extends JpaRepository {
} 测试代码
@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
@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
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)
spring.jpa.hibernate.naming.physical-strategy=com.git.hui.boot.jpacase.strategy.JpaNamingStrategyStandardImpl测试 case
@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
推荐博文
- 190612-SpringBoot 系列教程 JPA 之基础环境搭建
- 190614-SpringBoot 系列教程 JPA 之新增记录使用姿势
- 190623-SpringBoot 系列教程 JPA 之 update 使用姿势
- 190702-SpringBoot 系列教程 JPA 之 delete 使用姿势详解
- 190717-SpringBoot 系列教程 JPA 之 query 使用姿势详解之基础篇
- 191218-SpringBoot 系列教程 JPA 错误姿势之环境配置问题
源码
- 工程：https://github.com/liuyueyi/spring-boot-demo
- 项目: https://github.com/liuyueyi/spring-boot-demo/blob/master/spring-boot/102-jpa-errorcase2
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