Proposal: support Kotlin value classes (and other form of wrapped IDs)

[vladimirfx]

Kotlin value classes are perfect typed wrappers for typical singular entity IDs:

@Entity
class Order (
  @Id
  val id: OrderId

// more fields
)

@JvmInline
value class OrderId(val id: UUID)

Currently, enhancers see it as a wrapped type (UUID in the example) and persist works perfectly.

Problems arise when we try to query such entities:

1. Nor find not Quey can't convert values passed as is and see value class itself (OrderId)
2. AttributeConverters not used by Ebean for ID conversion.
3. There is no way to customize IdBinder.convertId - it is always delegated to ScalarType. But ScalarType for such properties is a wrapped type (UUID).

Simple reflection based value class unwrap function:

fun unwrapValueClass(id: Any): Any {
    val idClass = id::class
    return if (idClass.isValue) {
        @Suppress("UNCHECKED_CAST")
        (idClass.memberProperties.first() as KProperty1<Any, Any>).get(id)
    } else {
        id
    }
}

Current code thows:

java.lang.IllegalArgumentException: UUID string too large
	at java.util.UUID.fromString(UUID.java:199) ~[?:?]
	at io.ebeaninternal.server.core.BasicTypeConverter.toUUID(BasicTypeConverter.java:196) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.type.ScalarTypeUUIDBase.toBeanType(ScalarTypeUUIDBase.java:60) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.type.ScalarTypeUUIDBase.toBeanType(ScalarTypeUUIDBase.java:17) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.deploy.id.IdBinderSimple.convertId(IdBinderSimple.java:243) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.deploy.BeanDescriptor.convertId(BeanDescriptor.java:2231) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.core.DefaultServer.findIdCheckPersistenceContextAndCache(DefaultServer.java:1104) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.core.DefaultServer.findId(DefaultServer.java:1150) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.core.DefaultServer.find(DefaultServer.java:1056) ~[ebean-core-12.9.2.jar:?]
	at io.ebeaninternal.server.core.DefaultServer.find(DefaultServer.java:1044) ~[ebean-core-12.9.2.jar:?]
	at ru.citc.hcm.api.app.contact.EbeanPhoneRepository.findByIds_aroundBody6(EbeanPhoneRepository.kt:170) ~[main/:?]
	at ru.citc.hcm.api.app.contact.EbeanPhoneRepository$AjcClosure7.run(EbeanPhoneRepository.kt:1) ~[main/:?]
	at org.springframework.transaction.aspectj.AbstractTransactionAspect.ajc$around$org_springframework_transaction_aspectj_AbstractTransactionAspect$1$2a73e96cproceed(AbstractTransactionAspect.aj:67) ~[spring-aspects-5.3.10.jar:5.3.10]
	at org.springframework.transaction.aspectj.AbstractTransactionAspect$AbstractTransactionAspect$1.proceedWithInvocation(AbstractTransactionAspect.aj:73) ~[spring-aspects-5.3.10.jar:5.3.10]
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:388) ~[spring-tx-5.3.10.jar:5.3.10]
	at org.springframework.transaction.aspectj.AbstractTransactionAspect.ajc$around$org_springframework_transaction_aspectj_AbstractTransactionAspect$1$2a73e96c(AbstractTransactionAspect.aj:71) ~[spring-aspects-5.3.10.jar:5.3.10]
	at ru.citc.hcm.api.app.contact.EbeanPhoneRepository.findByIds(EbeanPhoneRepository.kt:1) ~[main/:?]
	at ru.citc.hcm.api.app.contact.PhoneMobileAppPublisher.onPhoneUserAssignmentChanged(PhoneMobileAppPublisher.kt:51) ~[main/:?]
	at ru.citc.hcm.api.app.contact.PhoneMobileAppPublisher.access$onPhoneUserAssignmentChanged(PhoneMobileAppPublisher.kt:21) ~[main/:?]
	at ru.citc.hcm.api.app.contact.PhoneMobileAppPublisher$3.invoke(PhoneMobileAppPublisher.kt:30) ~[main/:?]
	at ru.citc.hcm.api.app.contact.PhoneMobileAppPublisher$3.invoke(PhoneMobileAppPublisher.kt:30) ~[main/:?]
	at ru.citc.hcm.api.app.common.TypedEventBus.publish(TypedEventBus.kt:59) ~[main/:?]
...

Suggested solution:

1. Introduce a simple strategic interface to hook in id conversion. Implementation should convert value if it can or return null if it is not. In the latter case, current mechanics are used.
2. The Kotlin query generator should be enhanced to emit value classes instead of wrapped types in query beans.

[vladimirfx]

I can provide a PR.

[rbygrave]

I don't yet fully understand in that the expected approach is to have an AttributeConverter

AttributeConverters not used by Ebean for ID conversion.

If there was defined and registered (querybean-generator / kotlin-querybean-generator should automatically detect AttributeConverter's and include them in the generated code so that they are registered with ebean (without classpath scanning or need for developers to write code to register them).

So the expectation is to write an AttributeConverter and annotate it with @Converter so that it is detected via the querybean generator. Why are we not doing that for this case?

See example: https://github.com/ebean-orm/ebean/blob/master/kotlin-querybean-generator/src/test/kotlin/org/example/otherpackage/ValidEmailAttributeConverter.kt