Micronaut JDBC: using kotlin value classes as @Id

Question

Is it possible to use Kotlin value classes as @Id property?

Entity:

import io.micronaut.data.annotation.*

@JvmInline
value class UserId(val value: Int)

@MappedEntity("users")
data class User(
    @field:Id
    @field:GeneratedValue
    val id: Int = UserId(0),
    val name: String
)

Repo:

import io.micronaut.data.jdbc.annotation.JdbcRepository
import io.micronaut.data.model.query.builder.sql.Dialect
import io.micronaut.data.repository.CrudRepository

// Repo
@JdbcRepository(dialect = Dialect.POSTGRES)
interface UsersRepo : CrudRepository<User, UserId>

Currently, during compilation I am getting the following error:

error: Unable to implement Repository method: UsersRepo.update(Object entity). No identity is present

AFAIK, it is not possible with micronaut-data-jpa, but what about micronaut-data-jdbc?

Answer 1

You can achieve type checking without a value class by simply using a data class. The trick is that you need to write a mapper for each layer so that it 'remains hidden.' Naturally, the efficiency of this approach isn't as good due to the wrapping, but I assume the goal here is safety rather than micro-optimization; otherwise, the specific type would simply be written out.

package example.micronaut

import io.micronaut.core.convert.ConversionContext
import io.micronaut.core.convert.TypeConverter
import io.micronaut.core.type.Argument
import io.micronaut.data.annotation.Id
import io.micronaut.data.annotation.MappedEntity
import io.micronaut.data.annotation.TypeDef
import io.micronaut.data.model.DataType
import io.micronaut.data.model.runtime.convert.AttributeConverter
import io.micronaut.serde.*
import io.micronaut.serde.annotation.Serdeable
import jakarta.inject.Singleton
import java.util.*

@Serdeable
@MappedEntity
data class SaasSubscription(
    @Id val id: SaasSubscriptionId,
    val name: String,
    val cents: Int
)

@TypeDef(type = DataType.LONG, converter = SaasSubscriptionIdAttributeConverter::class)
class SaasSubscriptionId(
    val value: Long,
) {
    override fun toString(): String {
        return value.toString()
    }

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is SaasSubscriptionId) return false
        return value == other.value
    }

    override fun hashCode(): Int {
        return value.hashCode()
    }
}

/**
 * Data repository support.
 */
@Singleton
class SaasSubscriptionIdAttributeConverter : AttributeConverter<SaasSubscriptionId?, Long?> {

    override fun convertToPersistedValue(quantity: SaasSubscriptionId?, context: ConversionContext): Long? {
        return quantity?.value
    }

    override fun convertToEntityValue(value: Long?, context: ConversionContext): SaasSubscriptionId? {
        return if (value == null) null else SaasSubscriptionId(value)
    }

}

/**
 * Controller path variable support.
 */
@Singleton
class SaasSubscriptionIdConverter : TypeConverter<String, SaasSubscriptionId> {
    override fun convert(value: String, targetType: Class<SaasSubscriptionId>, context: ConversionContext): Optional<SaasSubscriptionId> {
        return Optional.of(SaasSubscriptionId(value.toLong()))
    }
}

/**
 * JSON request/response support.
 */
@Singleton
class SaasSubscriptionIdSerde : Serde<SaasSubscriptionId> {
    override fun deserialize(
        decoder: Decoder,
        context: Deserializer.DecoderContext,
        type: Argument<in SaasSubscriptionId>
    ): SaasSubscriptionId {
        return SaasSubscriptionId(decoder.decodeLong())
    }

    override fun serialize(
        encoder: Encoder,
        context: Serializer.EncoderContext,
        type: Argument<out SaasSubscriptionId>,
        value: SaasSubscriptionId
    ) {
        encoder.encodeLong(value.value)
    }
}