Spring Data R2dbc UUID @Id Persistable

Question

I am not sure whether this is a bug or I am using Persistable incorrectly. Aim: make the UserId non-null to avoid having to assert non-null when using in the code

User.kt

@Table(value = "main.user")
data class User(
    @Id
    @Column("id")
    var userId: UUID = UUID(0,0),
    val username: Username,
    val isVerified: Boolean = false,
    val updated: LocalDateTime,
    val updatedBy: String
) : Persistable<UUID> {
    override fun isNew(): Boolean = userId.equals(UUID(0,0))

    override fun getId(): UUID = userId
}

UserRepository.kt

@Repository
interface UserModelRepository : CoroutineCrudRepository<User, UUID>

Test.kt

@DataR2dbcTest
internal class Test {

    @Autowired
    private lateinit var userModelRepository: UserModelRepository

    @Test
    fun `should save the user model`() = runBlocking {
        val userModel = createUserModel()

        val actual = UserModelRepository.save(userModel)

        actual.userId shouldNotBe UUID(0, 0)
    }

}

SQL

CREATE TABLE IF NOT EXISTS main.user
(
    id                      UUID                         NOT NULL PRIMARY KEY DEFAULT GEN_RANDOM_UUID(),
    username                CHARACTER VARYING(70)        NOT NULL UNIQUE,
    is_verified             BOOLEAN                      NOT NULL,
    updated                 TIMESTAMP WITHOUT TIME ZONE  NOT NULL,
    updated_by              CHARACTER VARYING(255)       NOT NULL
);

Expected: The test to pass as the Id should be generated by the database Actual: Id is "00000000-0000-0000-0000-000000000000"

Answer 1

Spring Data uses the same object reference to apply the update of the ID at. Since you set the ID to a final value Spring Data can't apply a new generated ID to it. The ID will also only be generated if the value is null otherwise the value which is already set will be used.

There is a workaround:

@Table("my_user")
data class MyUser(
    @Id
    @Column("id")
    private var _id: UUID? = null,
    val name: String = "blubb"
) {
    val id: UUID
        get() = _id ?: UUID(0, 0)
}

But it is basically bad practice as answered here.