Java Spring中ReactiveCosmosRepository如何返回数值型查询结果？

问题描述 #

使用ReactiveCosmosRepository自定义查询返回数值（如MAX、COUNT计算结果）时抛出异常，返回实体类的查询可正常运行，但返回数值的查询始终失败，尝试过Mono<Integer>、Mono<Long>、Mono<Object>等多种返回类型均无效。

仓库代码 #

@Repository
public interface RepoCosmos extends ReactiveCosmosRepository<MyClass, String> {

    @Query("SELECT * FROM c WHERE c.Foo = @Foo")
    Mono<MyClass> get(@Param("Foo") String Foo);

    @Query("SELECT VALUE MAX(c.intID) FROM c WHERE NOT c.condition")
    Mono<?> getMaxIntID();

    @Query("SELECT VALUE COUNT(1) FROM c")
    Mono<?> test();
}

执行代码与异常 #

执行代码：

Mono<?> b = RepoCosmos.getMaxIntID();
b.block();

抛出异常：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2023-09-13 07:37:45.672 ERROR 19908 --- [           main] o.s.boot.SpringApplication               : Application run failed

java.lang.IllegalStateException: Failed to execute ApplicationRunner
        at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:785) ~[spring-boot-2.5.6.jar:2.5.6]
        at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:772) ~[spring-boot-2.5.6.jar:2.5.6]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:345) ~[spring-boot-2.5.6.jar:2.5.6]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.6.jar:2.5.6]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.6.jar:2.5.6]
        at com.careerswales.urlservice.UrlApplication.main(UrlApplication.java:13) ~[main/:na]
Caused by: java.lang.IllegalArgumentException: domain should contain @Id field or field named id
        at com.azure.spring.data.cosmos.repository.support.CosmosEntityInformation.getIdField(CosmosEntityInformation.java:317) ~[azure-spring-data-cosmos-3.17.0.jar:3.17.0]
        Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Assembly trace from producer [reactor.core.publisher.FluxMapFuseable] :
        reactor.core.publisher.Flux.map(Flux.java:6273)
        com.azure.spring.data.cosmos.core.ReactiveCosmosTemplate.runQuery(ReactiveCosmosTemplate.java:660)
Error has been observed at the following site(s):
        *________Flux.map ⇢ at com.azure.spring.data.cosmos.core.ReactiveCosmosTemplate.runQuery(ReactiveCosmosTemplate.java:660)
        *__Flux.usingWhen ⇢ at org.springframework.data.repository.core.support.RepositoryMethodInvoker$ReactiveInvocationListenerDecorator.decorate(RepositoryMethodInvoker.java:242)
        |_      Mono.from ⇢ at org.springframework.data.repository.util.ReactiveWrapperConverters$PublisherToMonoConverter.convert(ReactiveWrapperConverters.java:564)

解决方案 #

方法1：使用ReactiveCosmosTemplate直接执行查询 #

绕开Repository对实体类型的校验，直接注入ReactiveCosmosTemplate手动执行查询并转换结果：

@Autowired
private ReactiveCosmosTemplate cosmosTemplate;

public Mono<Integer> getMaxIntID() {
    String query = "SELECT VALUE MAX(c.intID) FROM c WHERE NOT c.condition";
    return cosmosTemplate.query(query, new CosmosQueryRequestOptions(), Integer.class)
                       .single();
}

public Mono<Long> testCount() {
    String query = "SELECT VALUE COUNT(1) FROM c";
    return cosmosTemplate.query(query, new CosmosQueryRequestOptions(), Long.class)
                       .single();
}

方法2：创建带@Id的包装类接收结果 #

如果坚持使用Repository接口，需要定义一个包含@Id字段的包装类来适配查询结果：

public class NumericResult {
    @Id
    private String id; // 可设固定值，仅用于框架校验
    private Number value;

    // 构造器、Getter、Setter
}

修改Repository方法，将查询结果映射到包装类：

@Query("SELECT {\"id\": \"max-id\", \"value\": MAX(c.intID)} FROM c WHERE NOT c.condition")
Mono<NumericResult> getMaxIntID();

@Query("SELECT {\"id\": \"count-id\", \"value\": COUNT(1)} FROM c")
Mono<NumericResult> test();

后续从NumericResult实例中取出value即可获得目标数值。

问题核心原因 #

Azure Spring Data Cosmos的Repository默认期望查询返回带@Id字段的实体类，当返回原始数值类型时，框架会尝试将结果映射为实体类，因找不到@Id字段触发异常。通过Template直接执行或用包装类适配，即可规避该校验逻辑。

内容的提问来源于stack exchange，提问作者Vhagar