How to parse generic key with kotlin serialization from JSON

Question

I am struggling with come up with idea how to properly parse JSON like this:

{
  "generic_key": { "version":1, "ttl":42 }
}

where expected kotlin class should look like this:

@Serializable
data class Config(val version: Int, val ttl: Long) {
  @Transient
  var key: String? = null // <== here comes generic_key
}

UPDATE

What I want to achieve is to get a kotlin class from string JSON and I don't know what key will be used as "generic_key".

UPDATE 2

Even something like this is okey for me:

@Serializable
data class ConfigWrapper(val map: Map<String, Config>)

Where there would be map with single item with key from jsonObject (e.g. generic_key) and with rest parsed with standard/generated Config.serializer.

Answer 1

Use the following data classes

   data class Config(
    
      @SerializedName("generic_key" ) var genericKey : GenericKey? = GenericKey()
    
    )
    
    data class GenericKey (
    
      @SerializedName("version" ) var version : Int? = null,
      @SerializedName("ttl"     ) var ttl     : Int? = null
    
    )

Answer 2

If the key is dynamic and different, the map structure should be fine

@Serializable
data class Config(val version: Int, val ttl: Long)

val result = JsonObject(mapOf("generic_key" to Config(1, 42)))

Answer 3

At the end this works for me, but if there is more straight forward solution let me know.

private val jsonDecoder = Json { ignoreUnknownKeys = true }
private val jsonConfig = "...."

val result = jsonDecoder.parseToJsonElement(jsonConfig)
result.jsonObject.firstNonNullOf { (key, value) ->
 config = jsonDecoder.decodeFromJsonElement<Config>(value).also {
   it.key = key // this is generic_key (whatever string)
 }
}