Convert a Map to a Data Class

Question

Is there an easy method in Kotlin to allow me to convert a Map to an arbitrary data class?

The Map I'm trying to convert has all of the keys of the required fields of the data class.

I've hunted around, but haven't been able to find anything that seems to talk about doing this in a very generic way.

I know that I can use ObjectMapper, but that requires an extra library. Looking for something that is available just with Kotlin.

Answer 1

Why not just use a map delegate?

class MyData(val map: Map<String, String>) {
    val foo by map
    val bar by map
}

Or you can wrap it using a companion object and call it using MyData.from(mymap)

data class MyData(val foo: String, val bar: String) {
    companion object {
        fun from(map: Map<String, String>) = object {
            val foo by map
            val bar by map

            val data = MyData(foo, bar)
        }.data
    }

Answer 2

using kotlin reflection to map constructor parameters to map values this generic function will work for any class that receives field data in the primary constructor

Works well with JSON dbs like firebase and was tested with Map objects from Firebase DocumentSnapshot.data

fun <T : Any> mapToObject(map: Map<String, Any>, clazz: KClass<T>) : T {
    //Get default constructor
    val constructor = clazz.constructors.first()
    
    //Map constructor parameters to map values
    val args = constructor
    .parameters
    .map { it to map.get(it.name) }
    .toMap()
   
    //return object from constructor call
    return constructor.callBy(args)
}

with some class

data class Person(val firs: String, val last: String)

use like this

mapToObject(map, Person::class)