定制转换器，用于具有数据存储实体的嵌套密封类

Question

我们有一个主要的对象模型，其中包含其他值的集合。这些事件是一组已知类型的类型，例如创建，错误，完成等...每个事件都有几个覆盖字段，但对于该事件的一些特定字段。对我们来说，将它们作为密封类型的数据类作为数据类是有意义的。我们正在使用GCP的数据存储和com.google.cloud:spring-cloud-gcp-starter-data-dataStore库>用于读写的库。

我们遇到的错误发生在datastoretemplate.findbyid（...）上，我们相信这与当供应实体的事件的密封类有关。 StackTrace：

Failed to instantiate com.PhoneExample.PhoneEntity$EventEntity using constructor fun <init>(): com.PhoneExample.PhoneEntity.EventEntity with arguments
org.springframework.data.mapping.model.MappingInstantiationException: Failed to instantiate com.PhoneExample.PhoneEntity$EventEntity using constructor fun <init>(): com.PhoneExample.PhoneEntity.EventEntity with arguments 
    at org.springframework.data.mapping.model.ReflectionEntityInstantiator.createInstance(ReflectionEntityInstantiator.java:79)
    at org.springframework.data.mapping.model.ClassGeneratingEntityInstantiator.createInstance(ClassGeneratingEntityInstantiator.java:89)
    at com.google.cloud.spring.data.datastore.core.convert.DefaultDatastoreEntityConverter.read(DefaultDatastoreEntityConverter.java:169)
    at com.google.cloud.spring.data.datastore.core.convert.DefaultDatastoreEntityConverter.read(DefaultDatastoreEntityConverter.java:54)
    at com.google.cloud.spring.data.datastore.core.convert.TwoStepsConversions.convertOnReadSingleEmbedded(TwoStepsConversions.java:205)
    at com.google.cloud.spring.data.datastore.core.convert.TwoStepsConversions.convertOnRead(TwoStepsConversions.java:183)
    at com.google.cloud.spring.data.datastore.core.convert.TwoStepsConversions.convertOnRead(TwoStepsConversions.java:130)
    at com.google.cloud.spring.data.datastore.core.convert.EntityPropertyValueProvider.getPropertyValue(EntityPropertyValueProvider.java:68)
    at com.google.cloud.spring.data.datastore.core.convert.EntityPropertyValueProvider.getPropertyValue(EntityPropertyValueProvider.java:54)
    at com.google.cloud.spring.data.datastore.core.convert.EntityPropertyValueProvider.getPropertyValue(EntityPropertyValueProvider.java:32)
    at org.springframework.data.mapping.model.PersistentEntityParameterValueProvider.getParameterValue(PersistentEntityParameterValueProvider.java:74)
    at org.springframework.data.mapping.model.ClassGeneratingEntityInstantiator.extractInvocationArguments(ClassGeneratingEntityInstantiator.java:276)
    at org.springframework.data.mapping.model.ClassGeneratingEntityInstantiator$EntityInstantiatorAdapter.createInstance(ClassGeneratingEntityInstantiator.java:248)
    at org.springframework.data.mapping.model.ClassGeneratingEntityInstantiator.createInstance(ClassGeneratingEntityInstantiator.java:89)
    at com.google.cloud.spring.data.datastore.core.convert.DefaultDatastoreEntityConverter.read(DefaultDatastoreEntityConverter.java:169)
    at com.google.cloud.spring.data.datastore.core.convert.DefaultDatastoreEntityConverter.read(DefaultDatastoreEntityConverter.java:54)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.convertEntityResolveDescendantsAndReferences(DatastoreTemplate.java:669)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.lambda$convertEntitiesForRead$15(DatastoreTemplate.java:657)
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
    at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1603)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.convertEntitiesForRead(DatastoreTemplate.java:659)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.findAllById(DatastoreTemplate.java:264)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.performFindByKey(DatastoreTemplate.java:246)
    at com.google.cloud.spring.data.datastore.core.DatastoreTemplate.findById(DatastoreTemplate.java:140)
    at com.PhoneExample.ExampleTest.processTest(ExampleTest.kt:17)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.PhoneExample.PhoneEntity$EventEntity]: Is it an abstract class?; nested exception is java.lang.InstantiationException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:215)
    at org.springframework.data.mapping.model.ReflectionEntityInstantiator.createInstance(ReflectionEntityInstantiator.java:77)
Caused by: java.lang.InstantiationException
    at java.base/jdk.internal.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at kotlin.reflect.jvm.internal.calls.CallerImpl$Constructor.call(CallerImpl.kt:41)
    at kotlin.reflect.jvm.internal.KCallableImpl.call(KCallableImpl.kt:108)
    at kotlin.reflect.jvm.internal.KCallableImpl.callDefaultMethod$kotlin_reflection(KCallableImpl.kt:159)
    at kotlin.reflect.jvm.internal.KCallableImpl.callBy(KCallableImpl.kt:112)
    at org.springframework.beans.BeanUtils$KotlinDelegate.instantiateClass(BeanUtils.java:854)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:196)

我试图使以下示例在维护我们使用的结构时尽可能最小。

class ExampleTest(private val datastoreTemplate: DatastoreTemplate) {
    fun processTest() {
        val phone = Phone(
            "123456789",
            ErrorEvent("Error-01", RuntimeException("some exception"), Instant.now())
        )

        val phoneEntity = datastoreTemplate.save(PhoneEntity(phone))
        datastoreTemplate.findById(phoneEntity.id, PhoneEntity::class.java)
    }
}

data class Phone(
    val id: String,
    val events: Event
)

abstract class BaseEvent {
    abstract val name: String
    abstract val time: Instant
}
sealed class Event : BaseEvent()

data class ErrorEvent(
    override val name: String,
    val error: Throwable,
    override val time: Instant
) : Event()


@Entity(name = "phone")
data class PhoneEntity(
    @Id
    val id: String,
    val events: EventEntity
) {
    companion object {
        operator fun invoke(phone: Phone) =
            with(phone) {
                PhoneEntity(
                    id,
                    EventEntity(events)
                )
            }
    }

    fun to(): Phone =
        Phone(
            id,
            events.to()
        )

    @Entity
    sealed class EventEntity {
        companion object {
            operator fun invoke(event: Event) =
                when (event) {
                    is ErrorEvent -> with(event) {
                        ErrorEventEntity(
                            name,
                            error,
                            time
                        )
                    }
                }
        }

        fun to(): Event =
            when (this) {
                is ErrorEventEntity ->
                    with(this) {
                        ErrorEvent(name, error, time)
                    }
            }

        data class ErrorEventEntity(
            val name: String,
            val error: Throwable,
            val time: Instant
        ) : EventEntity()
    }
}

我们尝试通过使用DataStoreCustomConversions来解决此问题，以为我们可以指定如何从保存的实体转到事件，但最终仍会出现相同的错误。在调试时，看起来自定义转换器正在DataStoreTemplate中注册，因此除非我们缺少其他内容，否则我认为这是正确的。

val EVENT_ENTITY_CONVERTER: Converter<PhoneEntity.EventEntity, Event> = object : Converter<PhoneEntity.EventEntity, Event> {
    override fun convert(eventEntity: PhoneEntity.EventEntity): Event {
        return eventEntity.to()
    }
}

@Configuration
class ConverterConfiguration {
    @Bean
    fun datastoreCustomConversions(): DatastoreCustomConversions {
        return DatastoreCustomConversions(
            listOf(
                EVENT_ENTITY_CONVERTER
            )
        )
    }
}

我已经尝试更改转换器实现，但没有任何区别。

因此，主要问题：

1. 在自定义转换器中，我们是否在不允许其帮助该过程的情况下做错了什么，或者转换器无法解决此问题？
2. 如果转换器无济于事，在我们的事件上使用密封类可以维护其他操作，这将使我们能够从数据存储中对其进行认可？
3. 我们应该这样做的另一种方法是我们的​​结构中会更好或任何明显的设计缺陷吗？

目前，我们有一些工作的工作，但它涉及将我们的现场性更改为数据类，然后将所有可能的领域用于所有儿童事件，并使它们无效。然后，每次施工最终都以一堆无关的磁场为零（事件 - ＆gt; Evententity and Evententity -gt; event）。感觉就像是一种灵活的解决方案，只是丑陋的。

任何建议或帮助将不胜感激，谢谢

Answer 1

异常迹线抱怨缺乏事件类别类别的无参数构造函数。

根据 https://kotlinlang.orgg/ docs/data-classes.html＃属性 - 列表中的class-body kotlin不会为数据类生成无参数构造函数，除非您为类中的值指定默认值。

我怀疑，如果您为Evententity Feild添加默认值，您将超越该例外，甚至可能会遇到新的例外。