java - 保存新对象时， react 性存储库引发异常

Question

我正在使用r2dbc，r2dbc-h2和实验性spring-boot-starter-data-r2dbc

implementation 'org.springframework.boot.experimental:spring-boot-starter-data-r2dbc:0.1.0.M1'
implementation 'org.springframework.data:spring-data-r2dbc:1.0.0.RELEASE' // starter-data provides old version
implementation 'io.r2dbc:r2dbc-h2:0.8.0.RELEASE'
implementation 'io.r2dbc:r2dbc-pool:0.8.0.RELEASE'

我已经创建了 react 库

public interface IJsonComparisonRepository extends ReactiveCrudRepository<JsonComparisonResult, String> {}

还添加了一个自定义脚本，该脚本可在启动时在H2中创建表

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

    @Bean
    public CommandLineRunner startup(DatabaseClient client) {
        return (args) -> client
            .execute(() -> {
                var resource = new ClassPathResource("ddl/script.sql");
                try (var is = new InputStreamReader(resource.getInputStream())) {
                    return FileCopyUtils.copyToString(is);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } })
            .then()
            .block();
    }
}

我的 r2dbc配置看起来像这样

@Configuration
@EnableR2dbcRepositories
public class R2dbcConfiguration extends AbstractR2dbcConfiguration {
    @Override
    public ConnectionFactory connectionFactory() {
        return new H2ConnectionFactory(
            H2ConnectionConfiguration.builder()
                .url("mem:testdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE")
                .username("sa")
                .build());
    }
}

我执行逻辑的服务如下所示

@Override
public Mono<JsonComparisonResult> updateOrCreateRightSide(String comparisonId, String json) {
    return updateComparisonSide(comparisonId, storedComparisonResult -> {
        storedComparisonResult.setRightSide(json);
        return storedComparisonResult;
    });
}

private Mono<JsonComparisonResult> updateComparisonSide(String comparisonId,
                                                        Function<JsonComparisonResult, JsonComparisonResult> updateSide) {
    return repository.findById(comparisonId)
        .defaultIfEmpty(createResult(comparisonId))
        .filter(result -> ComparisonDecision.NONE == result.getDecision()) // if not NONE - it means it was found and completed
        .switchIfEmpty(Mono.error(new NotUpdatableCompleteComparisonException(comparisonId)))
        .map(updateSide)
        .flatMap(repository::save);

}

private JsonComparisonResult createResult(String comparisonId) {
    LOGGER.info("Creating new comparison result: {}.", comparisonId);
    var newResult = new JsonComparisonResult();
    newResult.setDecision(ComparisonDecision.NONE);
    newResult.setComparisonId(comparisonId);
    return newResult;
}

域看起来像这样

@Table("json_comparison")
public class JsonComparisonResult {
    @Column("comparison_id")
    @Id
    private String comparisonId;
    @Column("left")
    private String leftSide;
    @Column("right")
    private String rightSide;
    // @Enumerated(EnumType.STRING) - no support for now
    @Column("decision")
    private ComparisonDecision decision;
    private String differences;

问题是，当我尝试将任何对象添加到数据库时，它会失败并出现异常

org.springframework.dao.TransientDataAccessResourceException: Failed to update table [json_comparison]. Row with Id [4] does not exist.
    at org.springframework.data.r2dbc.repository.support.SimpleR2dbcRepository.lambda$save$0(SimpleR2dbcRepository.java:91) ~[spring-data-r2dbc-1.0.0.RELEASE.jar:1.0.0.RELEASE]
    at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:96) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:73) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.MonoUsingWhen$MonoUsingWhenSubscriber.deferredComplete(MonoUsingWhen.java:276) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.FluxUsingWhen$CommitInner.onComplete(FluxUsingWhen.java:536) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:1858) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.Operators.complete(Operators.java:132) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:45) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]
    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.3.1.RELEASE.jar:3.3.1.RELEASE]

由于某种原因，在 save库类中的 SimpleR2dbcRepository期间，它并不认为 objectToSave是新的，但是由于它实际上不存在，因此无法更新。

// SimpleR2dbcRepository#save
@Override
@Transactional
public <S extends T> Mono<S> save(S objectToSave) {

    Assert.notNull(objectToSave, "Object to save must not be null!");

    if (this.entity.isNew(objectToSave)) { // not new
        ....
    }
}

为什么会发生，这是什么问题？

Answer 1

TL; DR:，Spring Data如何知道您的对象是新对象还是应该存在？

关系Spring数据存储库(JDBC和R2DBC两者)必须在[Reactive]CrudRepository.save(…)上区分给定对象是新对象还是数据库中是否存在该对象。执行save(…)操作会导致INSERT或UPDATE语句。发出错误的语句可能会导致主键冲突或无操作，因为标准SQL无法表达更新内容。

Spring Data JDBC | R2DBC默认使用@Id值的存在/不存在。生成的主键是一种广泛使用的机制。如果提供了主键，则该实体被认为是现有的。如果id值为null，则该实体被视为新实体。

在引用文档中了解有关Entity State Detection Strategies的更多信息。