Spring Data REST Custom Resource URI works for String but not Long - spring

Question

I have a model:
public class MyModel {
#Id private Long id;
private Long externalId;
// Getters, setters
}
I'd like to use externalId as my resource identifier:
#Configuration
static class RepositoryEntityLookupConfig extends RepositoryRestConfigurerAdapter {
#Override
public void configureRepositoryRestConfiguration(RepositoryRestConfiguration configuration) {
configuration
.withEntityLookup()
.forRepository(MyRepository.class, MyModel::getExternalId, MyRepository::findByExternalId);
}
}
If externalId is a String, this works fine. But since it's a number (Long)
public interface MyRepository extends JpaRepository<MyModel, Long> {
Optional<MyModel> findByExternalId(#Param("externalId") Long externalId);
}
when invoking: /myModels/1 I get:
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long
at org.springframework.data.rest.core.config.EntityLookupConfiguration$RepositoriesEntityLookup.lookupEntity(EntityLookupConfiguration.java:213) ~[spring-data-rest-core-2.6.4.RELEASE.jar:na]
at org.springframework.data.rest.core.support.UnwrappingRepositoryInvokerFactory$UnwrappingRepositoryInvoker.invokeFindOne(UnwrappingRepositoryInvokerFactory.java:130) ~[spring-data-rest-core-2.6.4.RELEASE.jar:na]
at org.springframework.data.rest.webmvc.RepositoryEntityController.getItemResource(RepositoryEntityController.java:524) ~[spring-data-rest-webmvc-2.6.4.RELEASE.jar:na]
at org.springframework.data.rest.webmvc.RepositoryEntityController.getItemResource(RepositoryEntityController.java:335) ~[spring-data-rest-webmvc-2.6.4.RELEASE.jar:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_111]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_111]
...
A separate custom EntityLookupSupport<MyModel> component class works.
Am I missing something to get it working for Long using method references in my RepositoryRestConfigurerAdapter?

Answer 1

Try to add this to your RepositoryEntityLookupConfig class:
#Override
public void configureConversionService(ConfigurableConversionService conversionService) {
conversionService.addConverter(String.class, Long.class, Long::parseLong);
super.configureConversionService(conversionService);
}

Answer 2

Do you really need to set configuration by yourself ? You could try to use spring-boot auto-configuration by adding #RepositoryRestResource annotation
#RepositoryRestResource(collectionResourceRel = "myModels", path = "myModels")
public interface MyRepository extends JpaRepository<MyModel, Long> {
Optional<MyModel> findByExternalId(#Param("externalId") Long externalId);
}
Also add #Entity on your model class
#Entity
public class MyModel {
#Id
private Long id;
#Column(name = "EXTERNAL_ID")
// Column annotation is not required if you respect case-sensitive
private Long externalId;
// Getters, setters
}

Answer 3

Apparently, the default BackendIdConverter (see DefaultIdConverter) does nothing with ID conversion and on the other hand Spring Data Rest cannot use the repository ID type. So, you have to either convert it yourself or configure your custom ID converter bean, for example:
#Bean
public BackendIdConverter myModelBackendIdConverter() {
return new BackendIdConverter() {
#Override
public Serializable fromRequestId(final String id, final Class<?> entityType) {
return Optional.ofNullable(id).map(Long::parseLong).orElse(null);
}
#Override
public boolean supports(final Class<?> delimiter) {
return MyModel.class.isAssignableFrom(delimiter);
}
#Override
public String toRequestId(final Serializable id, final Class<?> entityType) {
return Optional.ofNullable(id).map(Object::toString).orElse(null);
}
};
}
See also:
BackendIdHandlerMethodArgumentResolver
#BackendId

Answer 4

The signature of the method you are trying to call seems to be:
forRepository(Class<R> type, Converter<T,ID> identifierMapping,
EntityLookupRegistrar.LookupRegistrar.Lookup<R,ID> lookup)
I don't see how MyModel::getExternalId can be doing the necessary conversion.
I would try something like the following:
#Configuration
static class RepositoryEntityLookupConfig extends RepositoryRestConfigurerAdapter {
#Override
public void configureRepositoryRestConfiguration(RepositoryRestConfiguration configuration) {
configuration
.withEntityLookup()
.forRepository(MyRepository.class, Long::parseLong, MyRepository::findByExternalId);
}
}