Spring Data KeyValue中@KeySpace实体为何需要@Entity注解？

在Spring 3.1 + Java 17环境下实践Spring Data KeyValue时发现：若不给标注@KeySpace的实体添加@Entity注解，就无法创建对应的Repository，报错信息如下：

2023-10-21T10:17:06.706-05:00  INFO 3536 --- [           main] .RepositoryConfigurationExtensionSupport : Spring Data Map - Could not safely identify store assignment for repository candidate interface com.example.demo.sql.Repo; If you want this repository to be a Map repository, consider extending one of the following types with your repository: org.springframework.data.keyvalue.repository.KeyValueRepository

相关配置代码如下：

pom.xml配置 #

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>demo</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-keyvalue</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

application.properties配置 #

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=sa
spring.h2.console.enabled=true

spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.H2Dialect

实体与Repository代码 #

实体类 #

package com.example.demo.sql;

import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import org.springframework.data.keyvalue.annotation.KeySpace;

@KeySpace
// 移除@Entity注解就会触发报错
public class KeyValue {
    @Id
    public String key;
    public String value;
}

Repository接口 #

package com.example.demo.sql;

import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
@Repository
public interface Repo extends CrudRepository<KeyValue, String> {
}

启动类 #

package com.example.demo;

import com.example.demo.sql.Repo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.data.map.repository.config.EnableMapRepositories;

@SpringBootApplication
@EnableMapRepositories
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Bean
    public String bean(Repo repo) {
        return repo.toString();
    }
}

这不是教程的错误，而是项目同时引入Spring Data JPA和Spring Data KeyValue两个模块后，Spring Data的仓库自动识别机制出现冲突：

• 实体无@Entity注解时，JPA模块无法识别该实体，不会为其创建JPA仓库；
• 但你的Repository继承的是通用CrudRepository，而非Spring Data KeyValue专属的KeyValueRepository，导致Map Repository扩展无法确定该仓库应绑定到KeyValue存储；
• 添加@Entity注解后，JPA模块会接管该仓库并创建JPA实现类，因此不再报错，但此时实际使用的是JPA仓库而非KeyValue的Map仓库，与教程预期不符。

有两种可行的解决方式：

1. 让Repository继承KeyValue专属接口
   修改Repository接口，直接继承KeyValueRepository而非通用的CrudRepository，让Spring Data明确识别这是一个KeyValue仓库，无需依赖@Entity注解：

   package com.example.demo.sql;
   
   import org.springframework.data.keyvalue.repository.KeyValueRepository;
   import org.springframework.stereotype.Repository;
   
   @Repository
   public interface Repo extends KeyValueRepository<KeyValue, String> {
   }
   

2. 明确指定Map仓库的扫描范围
   若不想修改Repository的继承关系，可在@EnableMapRepositories中指定扫描包路径，同时排除JPA对该包的扫描以避免冲突：

   • 修改启动类注解：

     @SpringBootApplication
     @EnableMapRepositories(basePackages = "com.example.demo.sql")
     @EnableJpaRepositories(excludeFilters = @Filter(type = FilterType.REGEX, pattern = "com.example.demo.sql.*"))
     public class DemoApplication {
         // 启动类原有内容不变
     }
     

   • 同时移除实体类上的@Entity注解。

内容的提问来源于stack exchange，提问作者JustinKSU