我想将一些“数据”类对象转换/映射为类似的“数据”类对象。例如,Web 表单类到数据库记录类。
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} ${lastName}"
val age: Int, // copy of age
// maybe many fields exist here like address, card number, etc.
val tel: String // copy of tel
)
我在 Java 中将 ModelMapper 用于此类工作,但它不能使用,因为数据类是最终的(ModelMapper 创建 CGLib 代理来读取映射定义)。当我们打开这些类/字段时,我们可以使用 ModelMapper,但我们必须手动实现“数据”类的功能。 (参见 ModelMapper 示例:https://github.com/jhalterman/modelmapper/blob/master/examples/src/main/java/org/modelmapper/gettingstarted/GettingStartedExample.java)
如何在 Kotlin 中映射这样的“数据”对象?
更新: ModelMapper 自动映射具有相同名称的字段(如 tel -> tel),无需映射声明。我想用 Kotlin 的数据类来做。
更新: 每个类的用途取决于应用程序的类型,但它们可能被放置在应用程序的不同层中。
例如:
这些类相似,但又不相同。
出于以下原因,我想避免正常的函数调用:
当然,想要一个具有类似功能的库,但也欢迎 Kotlin 功能的信息(如在 ECMAScript 中传播)。
最佳答案
最简单(最好的?):
fun PersonForm.toPersonRecord() = PersonRecord(
name = "$firstName $lastName",
age = age,
tel = tel
)
反射(reflection)(表现不佳):
fun PersonForm.toPersonRecord() = with(PersonRecord::class.primaryConstructor!!) {
val propertiesByName = PersonForm::class.memberProperties.associateBy { it.name }
callBy(args = parameters.associate { parameter ->
parameter to when (parameter.name) {
"name" -> "$firstName $lastName"
else -> propertiesByName[parameter.name]?.get(this@toPersonRecord)
}
})
}
缓存反射(性能不错,但不如 #1 快):
open class Transformer<in T : Any, out R : Any>
protected constructor(inClass: KClass<T>, outClass: KClass<R>) {
private val outConstructor = outClass.primaryConstructor!!
private val inPropertiesByName by lazy {
inClass.memberProperties.associateBy { it.name }
}
fun transform(data: T): R = with(outConstructor) {
callBy(parameters.associate { parameter ->
parameter to argFor(parameter, data)
})
}
open fun argFor(parameter: KParameter, data: T): Any? {
return inPropertiesByName[parameter.name]?.get(data)
}
}
val personFormToPersonRecordTransformer = object
: Transformer<PersonForm, PersonRecord>(PersonForm::class, PersonRecord::class) {
override fun argFor(parameter: KParameter, data: PersonForm): Any? {
return when (parameter.name) {
"name" -> with(data) { "$firstName $lastName" }
else -> super.argFor(parameter, data)
}
}
}
fun PersonForm.toPersonRecord() = personFormToPersonRecordTransformer.transform(this)
Storing Properties in a Map
data class PersonForm(val map: Map<String, Any?>) {
val firstName: String by map
val lastName: String by map
val age: Int by map
// maybe many fields exist here like address, card number, etc.
val tel: String by map
}
// maps to ...
data class PersonRecord(val map: Map<String, Any?>) {
val name: String by map // "${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")}"
})
https://stackoverflow.com/questions/39199426/