Play JSON JsPath Conditional Types

Question

I receive JSON response from an upstream server that I do not have a control on, for modification.

The JSON could have the following format

{"data":[["Some_text","boolean",["key_string1","key_string2"]]]}

Or it could also show up as

{"data":[["Some_text","boolean","key_string2"]]}

Or it could show up as a combination of the two.

{"data":[["Some_text","boolean",["key_string1","key_string2"]],["Some_text","boolean","key_string2"]]}

Individually I can define the READS for each format if they don't mix. However, given that the data may be of mixed format, I am unable to wrap my head around how the Reads should be written so as to check if the underlying type is a string or array before transforming it?

Is it possible to say something like

  (
    (JsPath)(0).read[String] and
    (JsPath)(1).read[Boolean] and
    (JsPath)(2).read( **if type is simple, String OR if type is array, then seq** )
  )(SomeGloriousCaseClass)

How can I approach this problem of deserializing?

I have a pretty good idea of how to do it but could you link the underlying class you want it to be mapped to ? — Louis F.
Sure thing, I don't mind any format for the underlying class, if it solves the problem regarding deserializing. Currently I was using the following case class case class SomeGloriousCaseClass(initialPart: String, booleanPart: Boolean, theDifficultPart: Seq[String]). I don't even mind if everything gets converted into a sequence — Serendipity
as @cchantep replied, you should be able to read it as a JsValue and then it's up to you to write a function that given a JsValue, return a Seq[String]. I am thinking of a recursive method which match on the value, and if the value is a string concatenate it to the final seq if it is an array recurse over it. You might be able to do this with a foldLeft method — Louis F.
Better to read as JsArray, that's an easy first validation — cchantep

Louis F. Louis F. · Accepted Answer · 2016-12-01T13:19:01

For fun I implemented a solution. You might need to tweak it a bit :

private def toSeq(jsValue: JsValue): JsResult[Seq[String]] = {
    jsValue match {
      case JsArray(es:Seq[JsValue]) ⇒ sequence(es.map(e ⇒ toSeq(jsValue))).map(_.flatten)
      case JsString(s) ⇒ JsSuccess(s :: Nil)
      case _ ⇒ JsError("INVALID")
    }
  }

  private def sequence[A](seq:Seq[JsResult[A]]):JsResult[Seq[A]] = {
    seq.foldLeft(JsResult.applicativeJsResult.pure(Seq[A]()))((acc, next) ⇒ for(acc2 ← acc; next2 ← next) yield acc2 :+ next2)
  }

Hope it helps and would be glad to provide further explanations if needed.

Play JSON JsPath Conditional Types

1 Answers