Allow to use Kotlin value classes directly as JpaRepository Id type

[igorwojda]

Consider this entity

@Entity
@Table(name = "project")
class ProjectJpa(

    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    val id: ProjectId,

    @Column(name = "name", nullable = false)
    val name: String,
)

The id is defined as Kotlin value class that is just a wrapper for the UUID:

value class ProjectId(val id: UUID)

Define repo with ProjectId as id

@Repository
interface ProjectJpaRepository : JpaRepository<ProjectJpa, ProjectId>

With the above code project can be saved to database:

projectJpaRepository.save(project.toJpa())

Problem
Retrieving project using findById...

projectJpaRepository.findById(ProjectId(UUID.fromString("1ec87062-89dd-4f75-a7a2-be7631332bbb")))

... results in 'org.springframework.dao.InvalidDataAccessApiUsageException' exception.:

Provided id of the wrong type for class com.mango.persistence.entity.ProjectJpa. Expected: 
class java.util.UUID, got class com.mango.business.model.value.ProjectId

[mp911de]

Do you have minimal sample that reproduces the problem for us?

Generally, we do not yet support inline classes because Kotlin compiles bytecode that isn't aligning well with bean property names and constructor resolution requires as well some workarounds.

[igorwojda]

Here it is
sample-2840.zip

[mp911de]

Kotlin compiles ProjectJpa to:

class ProjectJpa {

UUID id; // Kotlin: ProjectId
}

while the repository declaration remains at ProjectJpaRepository extends JpaRepository<ProjectJpa, ProjectId>. This difference between the declarations causes the identifier mismatch. You could switch the repository declaration to JpaRepository<ProjectJpa, UUID>.

There's not much we can do here. Kotlin aims to provide a lot of value at the code frontend at the price of compatibility between components.