Type initialization with jackson? - kotlin

Question

I'm working on data class extension with polymorphic property. Here's the dataclass:
import com.fasterxml.jackson.annotation.JsonSubTypes
import com.fasterxml.jackson.annotation.JsonTypeInfo
data class CarModelResponse(
val models: List<CarType> = listOf(),
)
#JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
#JsonSubTypes(
JsonSubTypes.Type(MercedesType::class, name = "mercedes"),
JsonSubTypes.Type(OpelType::class, name = "opel"),
)
abstract class CarType(open val type: String) {
abstract fun getCarFeature(): Any
}
data class MercedesType(
val comfortClass: Int
) : CarType("mercedes") {
override fun getCarFeature(): Int = comfortClass
}
data class OpelType(
val coupon: String
) : CarType("opel") {
override fun getCarFeature(): String = coupon
}
and also i have a test, where i'm trying to get a typed car variable:
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import org.junit.jupiter.api.Test
class CarResponseTest {
#Test
fun getCarFeatures() {
val json: String = """
{
"models": [
{
"type": "mercedes",
"comfortClass": 1
},
{
"type": "opel",
"coupon": "Buy Opel and win a Mercedes! Coupon #1."
}
]
}""".trimIndent()
val response = jacksonObjectMapper().readValue<CarModelResponse>(json)
val comfortClass: Int = (response.models.first() as MercedesType).getCarFeature()
val couppon: String = (response.models.last() as OpelType).getCarFeature()
}
}
Deserialization works fine, but I need to retrieve car's feature without casting with as at last two lines of code, but I'm a little stuck how to do that. Could anyone advice how can I get rid of it?

Answer 1

You can't do it with no casting, because compiler needs to know what type must be assigned, however in this case you can avoid casting to MercedesType or OpelType:
val comfortClass: Int = response.models.first().getCarFeature() as Int
val coupon: String = response.models.last().getCarFeature() as String