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| Nacos | ||
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| # SpringBoot系列JPA错误姿势之Entity映射 | ||
| # 102-jpa-errocase2 | ||
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| 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？ | ||
| mysql的field映射为POJO的正确使用姿势，对应的博文: | ||
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| <!-- more --> | ||
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| ## I. 映射问题 | ||
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| ### 1. 项目基本配置 | ||
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| 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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| ```xml | ||
| <dependency> | ||
| <groupId>org.springframework.boot</groupId> | ||
| <artifactId>spring-boot-starter-data-jpa</artifactId> | ||
| </dependency> | ||
| <dependency> | ||
| <groupId>mysql</groupId> | ||
| <artifactId>mysql-connector-java</artifactId> | ||
| </dependency> | ||
| ``` | ||
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| 项目配置文件`application.properties` | ||
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| ```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 | ||
| ``` | ||
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| 表结构 | ||
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| ```sql | ||
| 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'; | ||
| ``` | ||
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| ### 2. 错误case | ||
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| 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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| ```java | ||
| @Data | ||
| @Entity | ||
| @Table(name = "meta_group") | ||
| public class ErrorMetaGroupPo { | ||
| @Id | ||
| @GeneratedValue(strategy = GenerationType.IDENTITY) | ||
| private Integer id; | ||
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| @Column(name = "group") | ||
| private String group; | ||
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| @Column(name = "profile") | ||
| private String profile; | ||
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| @Column(name = "desc") | ||
| private String desc; | ||
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| @Column(name = "deleted") | ||
| private Integer deleted; | ||
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| @Column(name = "create_time") | ||
| private Timestamp createTime; | ||
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| @Column(name = "update_time") | ||
| private Timestamp updateTime; | ||
| } | ||
| ``` | ||
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| 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？ | ||
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| 先写一个对应的Repository来实测一下 | ||
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| ```java | ||
| public interface ErrorGroupJPARepository extends JpaRepository<ErrorMetaGroupPo, Integer> { | ||
| } | ||
| ``` | ||
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| 测试代码 | ||
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| ```java | ||
| @Component | ||
| public class GroupManager { | ||
| @Autowired | ||
| private ErrorGroupJPARepository errorGroupJPARepository; | ||
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| 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(); | ||
| } | ||
| } | ||
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| 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(); | ||
| } | ||
| } | ||
| ``` | ||
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|  | ||
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| 从输出结果来看，提示的是sql异常，why? | ||
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| - group,desc 为关键字，拼sql的时候需要用反引号包裹起来 | ||
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| ### 3. 正确姿势一 | ||
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| 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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| ```java | ||
| @Data | ||
| @Entity | ||
| @Table(name = "meta_group") | ||
| public class MetaGroupPO { | ||
| @Id | ||
| @GeneratedValue(strategy = GenerationType.IDENTITY) | ||
| private Integer id; | ||
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| @Column(name = "`group`") | ||
| private String group; | ||
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| @Column(name = "`profile`") | ||
| private String profile; | ||
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| @Column(name = "`desc`") | ||
| private String desc; | ||
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| @Column(name = "`deleted`") | ||
| private Integer deleted; | ||
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| @Column(name = "`create_time`") | ||
| private Timestamp createTime; | ||
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| @Column(name = "`update_time`") | ||
| private Timestamp updateTime; | ||
| } | ||
| ``` | ||
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| ### 4. 正确姿势二 | ||
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| 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 | ||
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| 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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| ```java | ||
| public class JpaNamingStrategyStandardImpl extends PhysicalNamingStrategyStandardImpl { | ||
| @Setter | ||
| private static int mode = 0; | ||
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| @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; | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| 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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| ```properties | ||
| spring.jpa.hibernate.naming.physical-strategy=com.git.hui.boot.jpacase.strategy.JpaNamingStrategyStandardImpl | ||
| ``` | ||
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| 测试case | ||
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| ```java | ||
| @SpringBootApplication | ||
| public class Application { | ||
| public Application(GroupManager groupManager) { | ||
| groupManager.test(); | ||
| } | ||
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| public static void main(String[] args) { | ||
| JpaNamingStrategyStandardImpl.setMode(1); | ||
| SpringApplication.run(Application.class, args); | ||
| } | ||
| } | ||
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| @Component | ||
| public class GroupManager { | ||
| @Autowired | ||
| private ErrorGroupJPARepository errorGroupJPARepository; | ||
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| @Autowired | ||
| private GroupJPARepository groupJPARepository; | ||
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| 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(); | ||
| } | ||
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| try { | ||
| int id2 = addGroup2(group, profile, desc); | ||
| System.out.println("add2: " + groupJPARepository.findById(id2)); | ||
| } catch (Exception e) { | ||
| e.printStackTrace(); | ||
| } | ||
| } | ||
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| 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(); | ||
| } | ||
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| 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(); | ||
| } | ||
| } | ||
| ``` | ||
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| 执行之后输出: | ||
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|  | ||
| - [200103-SpringBoot系列JPA错误姿势之Entity映射](http://spring.hhui.top/spring-blog/2020/01/03/200103-SpringBoot%E7%B3%BB%E5%88%97JPA%E9%94%99%E8%AF%AF%E5%A7%BF%E5%8A%BF%E4%B9%8BEntity%E6%98%A0%E5%B0%84/) |
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