Every backend eventually hits the same wall: a domain concept needs a different shape at every layer it touches. One model becomes three, and someone has to write — and maintain — the code that translates between them.
In a typical Kotlin backend, a single concept like User needs a parallel data structure to be persisted:
data class User(val id: UUID, val email: String)
data class UserEntity(val id: String, val email: String)
fun User.toUserEntity(): UserEntity = UserEntity(id.toString(), email)
