serialize Map with key and value as case class using circe - json

Question

Below is the simplified code that has a Map with key and value as case class.
Key and value object are successfully serialized with circe.
But facing challenge to serialize Map[CaseClassKey, CaseClassValue] with circe.
//////case classes and common vals starts here//////
case class Person(personId : Int, phoneNumber : Int)
case class Item(name : String)
case class Basket(items : List[Item], bills : Map[Int, Int])
def createBasketInstance() : Basket = {
val milk = Item("milk")
val coffee = Item("coffee")
val bills = Map(1 -> 20, 2 -> 75)
Basket( List(milk, coffee), bills )
}
val basket = createBasketInstance()
val person = Person(1, 987654)
//////case classes and common vals ends here//////
import io.circe._
import io.circe.generic.semiauto._
import io.circe.syntax._
import io.circe.parser._
//Serializing Person instance that is used as Key in Map
{
implicit val personCodec :Codec[Person] = deriveCodec[Person]
val jsonString = person.asJson.spaces2
println(jsonString)
}
println("-" * 50)
//Serializing Basket instance that is used as Value in Map
{
implicit val itemCodec :Codec[Item] = deriveCodec[Item]
implicit val basketCodec :Codec[Basket] = deriveCodec[Basket]
val jsonString = basket.asJson.spaces2
println(jsonString)
}
println("-" * 50)
//Serializing Map[Person, Basket]
//TODO : not able to make it work
{
implicit val itemCodec :Codec[Item] = deriveCodec[Item]
implicit val basketCodec :Codec[Basket] = deriveCodec[Basket]
val map = Map(person -> basket)
//TODO : How to make below lines work
//val jsonString = map.asJson.spaces2
//println(jsonString)
}
scalafiddle link : https://scalafiddle.io/sf/SkZNa1L/2
Note : Looking to just serialize and deserialize data (Map[Person, Basket]) correctly. How json looks is not really important in this particular case.

Answer 1

Strictly speaking, you are trying to create an invalid json.
Json map structure isn't an arbitrary map, it's an object structure where keys are property names.
https://www.json.org/json-en.html
See also Can we make object as key in map when using JSON?
Update:
I suggest a slight change to your model to get the job done.
Instead of Map use array of objects, each having two properties: key and value
Something like this:
case class Entry(key: Person, value: Basket)
So you can replace Map[Person, Basket] with Seq[Entry], and convert it back to Map if needed.