Converting JSON field names in argonaut

Question

I'm writing a library to convert JSON responses from an API for backwards compatibility reasons. And what I need to do is take in arbitrary JSON, and change certain field names. I'm using scala and argonaut, but I don't see any way in the docs or examples of changing the FIELD names, only the values.

Answer 1

I ended up folding over the object I need to convert and adding to a map, and then creating a new json object.

val conversionMap = Map("a" -> "b")

Json(
  j.objectOrEmpty.toMap.foldLeft(Map.empty[JsonField, Json]) {
    case (acc, (key, value)) =>
      acc.updated(conversionMap.getOrElse(key, key), j.fieldOrNull(key))
  }.toSeq: _*
)

Answer 2

I don't know of a particularly nice way to do this, but it's not too awful to write a helper that will replace a field in an object and then use that in a cursor with withObject:

def renameField(before: JsonField, after: JsonField)(obj: JsonObject) =
  obj(before).map(v => (obj - before) + (after, v)).getOrElse(obj)

Parse.parseOption("""{ "a": { "b": { "c": 1 } } }""").flatMap { json =>
  (json.hcursor --\ "a").withFocus(_.withObject(renameField("b", "z"))).undo
}

This will return Some({"a":{"z":{"c":1}}}) as expected.