How to convert a Kotlin data class object to map?

Question

Is there any easy way or any standard library method to convert a Kotlin data class object to a map/dictionary of its properties by property names? Can reflection be avoided?

Answer 1

I was using the jackson method, but turns out the performance of this is terrible on Android for first serialization (github issue here). And its dramatically worse for older android versions, (see benchmarks here)

But you can do this much faster with Gson. Conversion in both directions shown here:

import com.google.gson.Gson
import com.google.gson.reflect.TypeToken

val gson = Gson()

//convert a data class to a map
fun <T> T.serializeToMap(): Map<String, Any> {
    return convert()
}

//convert a map to a data class
inline fun <reified T> Map<String, Any>.toDataClass(): T {
    return convert()
}

//convert an object of type I to type O
inline fun <I, reified O> I.convert(): O {
    val json = gson.toJson(this)
    return gson.fromJson(json, object : TypeToken<O>() {}.type)
}

//example usage
data class Person(val name: String, val age: Int)

fun main() {

    val person = Person("Tom Hanley", 99)

    val map = mapOf(
        "name" to "Tom Hanley", 
        "age" to 99
    )

    val personAsMap: Map<String, Any> = person.serializeToMap()

    val mapAsPerson: Person = map.toDataClass()
}

Answer 2

This extension function uses reflection, but maybe it'll help someone like me coming across this in the future:

inline fun <reified T : Any> T.asMap() : Map<String, Any?> {
    val props = T::class.memberProperties.associateBy { it.name }
    return props.keys.associateWith { props[it]?.get(this) }
}