Kovaを使ってParse don't Validateの実現

ReserveTourInput.kt

package example

import org.komapper.extension.validator.Kova
import org.komapper.extension.validator.ObjectSchema
import org.komapper.extension.validator.ValidationResult
import org.komapper.extension.validator.factory.generateFactory
import org.komapper.extension.validator.factory.tryCreate
import org.komapper.extension.validator.isInt
import org.komapper.extension.validator.isNullOr
import org.komapper.extension.validator.isSuccess
import org.komapper.extension.validator.max
import org.komapper.extension.validator.min
import org.komapper.extension.validator.notNull
import org.komapper.extension.validator.then
import org.komapper.extension.validator.toInt
import org.komapper.extension.validator.toNonNullable

// このサンプルコードは以下のページにあるJava版のコードをKotlinのライブラリ（https://github.com/komapper/kova）を使って書き換えたものです
// https://scrapbox.io/kawasima/バリデーション解体新書

data class ReserveTourInput(
    val tourCode: String,
    val adultCount: Int,
    val childCount: Int,
    val remarks: String?,
) {
    companion object : ObjectSchema<ReserveTourInput>() {
        private val intStringValidator = Kova.nullable<String>().notNull().toNonNullable().then { it.isInt().toInt() }
        private val countValidator = Kova.int().min(0).max(5)

        fun parse(tourCode: String, adultCount: String?, childCount: String?, remarks: String?): ValidationResult<ReserveTourInput> {
            val factory = generateFactory("ReserveTourInput") {
                val tourCode = check("tourCode", tourCode) { it.min(1).max(10) }
                val adultCount = check("adultCount", adultCount) { intStringValidator.then(countValidator) }
                val childCount = check("childCount", childCount) { intStringValidator.then(countValidator) }
                val remarks = check("remarks", remarks) { it.isNullOr({ it.min(0).max(80)}) }
                create { ReserveTourInput(tourCode(), adultCount(), childCount(), remarks()) }
            }
            return factory.tryCreate()
        }
    }
}

fun main() {
    println("検証成功の例")
    val result1 = ReserveTourInput.parse("123", "2", "3", "remarks")
    if (result1.isSuccess()) {
        println(result1.value)
        // ReserveTourInput(tourCode=123, adultCount=2, childCount=3, remarks=remarks)
    } else {
        error("never happens")
    }

    println("検証失敗の例")
    val result2 = ReserveTourInput.parse("", "10", "-1", "remarks")
    if (result2.isSuccess()) {
        error("never happens")
    } else {
        println(result2.messages.joinToString("\n"))
        // Message(constraintId=kova.charSequence.min, text='must be at least 1 characters', root=ReserveTourInput, path=tourCode, input=)
        // Message(constraintId=kova.comparable.max, text='must be less than or equal to 5', root=ReserveTourInput, path=adultCount, input=10)
        // Message(constraintId=kova.comparable.min, text='must be greater than or equal to 0', root=ReserveTourInput, path=childCount, input=-1)
    }
}