Add nested fields to a JSON using Circe

Question

Problem

How can I add fields to a Json object if the field is nested?

This is similar to this forum: Adding field to a JSON using Circe

but instead of:

{
  ExistingField: {},
  "Newfield" : {}
}

my end goal is something like:

{
  ExistingField: {},
  "A" : {
    "B" : {
      "C" : "myStringValue"
    }
  },
  "AA" : {
    "BB" : "myStringValue" 
  }
}

Tried

I have a list of nested fields of type String that I would like to iterate through and add.
Instead of them being nested, I just got:

{
  ExistingField: {},
  "A.B.C" : "myStringValue"
}

my list of fields look like:

val listOfFields: List[String] = List("A.B.C", "AA.BB")

EDIT: What if the added field is an array? for example:

{
  ExistingField: {},
  "A" : {
    "B" : {
      "C" : "myStringValue"
    }
  },
  "AA" : {
    "BB" : [
      {
        "CC": "myStringValue"
      },
      {
        "CC": "myStringValue"
      }
    ]
  }
}

Answer 1

The recursive function uses pattern matching to convert a list of subfields (from splitting fields by the delimiter) into a nested Json which can then be deepMerged into the original Json. The foldLeft does this repeatedly for each field originally listed.

import io.circe.generic.auto._
import io.circe.parser
import io.circe.syntax._
import io.circe.Json

val jsonStr = """{"Fieldalreadythere": {}}"""

val jsonParse = parser.parse(jsonStr)


val listOfFields: List[String] = List("A.B.C", "AA.BB")

val listOfSplitFields = listOfFields.map(_.split("\\.").toList)


def makeJson(list: List[String]): Json = {
  list match {
    case h :: Nil => Json.fromFields(List((h, Json.fromString("stringValue"))))
    case h :: t => Json.fromFields(List(h -> makeJson(t)))
    case Nil => Json.fromFields(Nil)
  }
}


val originalJson = jsonParse match {
       case Right(value) => value.asObject
       case Left(error) => throw error
    }


val updateJsons = listOfSplitFields.map(makeJson(_))
updateJsons.foldLeft(originalJson.asJson)(_.deepMerge(_))

Result (of type io.circe.Json):

{
  "AA" : {
    "BB" : "stringValue"
  },
  "A" : {
    "B" : {
      "C" : "stringValue"
    }
  },
  "Fieldalreadythere" : {

  }
}