将Kotlin数据对象映射到数据对象的更好方法

Question

data class PersonForm(
    val firstName: String,
    val lastName: String,
    val age: Int,
    // maybe many fields exist here like address, card number, etc.
    val tel: String
)
// maps to ...
data class PersonRecord(
    val name: String, // "${firstName} ${lastName}"
    val age: Int, // copy of age
    // maybe many fields exist here like address, card number, etc.
    val tel: String // copy of tel
)

更新：每个类的用途取决于哪种应用程序，但这些类可能被放置在应用程序的不同层中。

例如：

• 数据从数据库（数据库实体）到HTML表单（模型/视图模型）的数据
• REST API结果到数据库的数据

null

当然，一个具有类似特性的库是有意的，但是Kotlin特性的信息也是受欢迎的（比如在ECMAScript中传播）。

Answer 1

>

最简单（最好？）：

fun PersonForm.toPersonRecord() = PersonRecord(
        name = "$firstName $lastName",
        age = age,
        tel = tel
)

反思（不是很好的表现）：

fun PersonForm.toPersonRecord() = with(PersonRecord::class.primaryConstructor!!) {
    val propertiesByName = PersonForm::class.memberProperties.associateBy { it.name }
    callBy(args = parameters.associate { parameter ->
        parameter to when (parameter.name) {
            "name" -> "$firstName $lastName"
            else -> propertiesByName[parameter.name]?.get(this@toPersonRecord)
        }
    })
}

缓存反射（性能不错，但不如#1):

open class Transformer<in T : Any, out R : Any>
protected constructor(inClass: KClass<T>, outClass: KClass<R>) {
    private val outConstructor = outClass.primaryConstructor!!
    private val inPropertiesByName by lazy {
        inClass.memberProperties.associateBy { it.name }
    }

    fun transform(data: T): R = with(outConstructor) {
        callBy(parameters.associate { parameter ->
            parameter to argFor(parameter, data)
        })
    }

    open fun argFor(parameter: KParameter, data: T): Any? {
        return inPropertiesByName[parameter.name]?.get(data)
    }
}

val personFormToPersonRecordTransformer = object
: Transformer<PersonForm, PersonRecord>(PersonForm::class, PersonRecord::class) {
    override fun argFor(parameter: KParameter, data: PersonForm): Any? {
        return when (parameter.name) {
            "name" -> with(data) { "$firstName $lastName" }
            else -> super.argFor(parameter, data)
        }
    }
}

fun PersonForm.toPersonRecord() = personFormToPersonRecordTransformer.transform(this)

data class PersonForm(val map: Map<String, Any?>) {
    val firstName: String   by map
    val lastName: String    by map
    val age: Int            by map
    // maybe many fields exist here like address, card number, etc.
    val tel: String         by map
}

// maps to ...
data class PersonRecord(val map: Map<String, Any?>) {
    val name: String    by map // "${firstName} ${lastName}"
    val age: Int        by map // copy of age
    // maybe many fields exist here like address, card number, etc.
    val tel: String     by map // copy of tel
}

fun PersonForm.toPersonRecord() = PersonRecord(HashMap(map).apply {
    this["name"] = "${remove("firstName")} ${remove("lastName")}"
})