RepositoryRestResource GET request issues

[dmitry-s]

RepositoryRestResource GET requests are failing if the id type is not Key. For example this would fail:

@RepositoryRestResource(collectionResourceRel = "traders", path = "traders")
public interface TraderRepository extends SpannerRepository<Trader, String> {
}

Error:

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [com.google.cloud.spanner.Key] to type [java.lang.String]
	at org.springframework.core.convert.support.GenericConversionService.handleConverterNotFound(GenericConversionService.java:321) ~[spring-core-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:194) ~[spring-core-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:174) ~[spring-core-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.data.repository.support.ReflectionRepositoryInvoker.convertId(ReflectionRepositoryInvoker.java:289) ~[spring-data-commons-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.data.repository.support.CrudRepositoryInvoker.invokeFindById(CrudRepositoryInvoker.java:92) ~[spring-data-commons-2.2.0.RELEASE.jar:2.2.0.RELEASE]
	at org.springframework.data.rest.core.support.UnwrappingRepositoryInvokerFactory$UnwrappingRepositoryInvoker.invokeFindById(UnwrappingRepositoryInvokerFactory.java:94) ~[spring-data-rest-core-3.2.0.RELEASE.jar:3.2.0.RELEASE]
	at org.springframework.data.rest.webmvc.RepositoryEntityController.getItemResource(RepositoryEntityController.java:518) ~[spring-data-rest-webmvc-3.2.0.RELEASE.jar:3.2.0.RELEASE]
	at org.springframework.data.rest.webmvc.RepositoryEntityController.getItemResource(RepositoryEntityController.java:331) ~[spring-data-rest-webmvc-3.2.0.RELEASE.jar:3.2.0.RELEASE]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
	at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.2.0.RELEASE.jar:5.2.0.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.0.RELEASE.jar:5.2.0.RELEASE]

To make it work, use Key for id type.

@RepositoryRestResource(collectionResourceRel = "traders", path = "traders")
public interface TraderRepository extends SpannerRepository<Trader, Key> {
}

[dmitry-s]

The problem is we use a custom BackendIdConverter to enable String to Key conversion. But the rest repository could have different ID type. We support 'virtual' keys in order to allow composite keys.
Because of that we allow users to create repositories with the following id types: Key, Object[],Iterable

Also we support regular id types, such as String.

BackendIdConverter doesn't know what was the ID type on the repository, it only has access to the entity.
After Spring gets id of type Key from BackendIdConverter it tries to convert it to the actual ID type of the repository (ReflectionRepositoryInvoker.java, Object convertId(Object id)). But it doesn't use the global conversion service so we can't provide a converter that can be used there.

@mp911de do you have any recommendations?