SpringBoot 系列 JPA 錯誤姿式之 Entity 映射

時間 2020-01-13

標籤 springboot 系列 jpa 錯誤 entity 映射欄目 Spring 简体版

原文原文鏈接

SpringBoot 系列 JPA 錯誤姿式之 Entity 映射java

本篇爲 JPA 錯誤使用姿式第二篇，java 的 POJO 類與數據庫表結構的映射關係，除了駝峯命名映射爲下劃線以外，還會有什麼別的坑麼？mysql

git

I. 映射問題

1. 項目基本配置

首先搭建基本的 springboot + jpa 項目，咱們使用的 springboot 版本爲2.2.1.RELEASE，mysql 版本 5+github

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

項目配置文件application.propertiesspring

## 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

表結構sql

CREATE TABLE `meta_group` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `group` varchar(32) NOT NULL DEFAULT '' COMMENT '分組',
  `profile` varchar(32) NOT NULL DEFAULT '' COMMENT 'profile 目前用在應用環境 取值 dev/test/pro',
  `desc` varchar(64) NOT NULL DEFAULT '' COMMENT '解釋說明',
  `deleted` int(4) NOT NULL DEFAULT '0' COMMENT '0表示有效 1表示無效',
  `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '建立時間',
  `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改時間',
  PRIMARY KEY (`id`),
  KEY `group_profile` (`group`,`profile`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COMMENT='業務配置分組表';

2. 錯誤 case

java 變量命名推薦的是駝峯命名方式，所以與數據庫中字段的下劃線方式須要關聯映射，經過 jpa 的相關知識學習，咱們知道可使用@Column註解來處理，因此有下面這種寫法數據庫

@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;
}

從命名上就能夠看出上面這種 case 是錯誤的，那麼究竟是什麼問題呢？springboot

先寫一個對應的 Repository 來實測一下app

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

測試代碼dom

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

    public void test() {
        String group = UUID.randomUUID().toString().substring(0, 4);
        String profile = "dev";
        String desc = "測試jpa異常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();
    }
}

從輸出結果來看，提示的是 sql 異常，why?

group,desc 爲關鍵字，拼 sql 的時候須要用反引號包裹起來

3. 正確姿式一

第一種正確使用姿式，直接在@column的 name 中，添加反引號包裹起來

@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. 正確姿式二

除了上面的 case 以外，還有另一種通用的方式，實現自定義的PhysicalNamingStrategy，實現字段映射

好比咱們自定義JpaNamingStrategyStandardImpl繼承自默認的PhysicalNamingStrategyStandardImpl策略，而後在字段名中，對於沒有引號的包裹的字段名主動添加一個反引號

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，須要修改配置文件(application.properties)

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

測試 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 = "測試jpa異常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();
    }
}

執行以後輸出: