Parsing complex JSON with JSON Combinators in Play

Question

I'm trying to parse the data from GovTrack, for example, https://www.govtrack.us/api/v2/bill/74369 . But titles is in a peculiar format:

"titles": [
 [
  "short", 
  "introduced", 
  "Public Online Information Act of 2011"
 ], 
 [
  "official", 
  "introduced", 
  "To establish an advisory committee to issue nonbinding governmentwide guidelines..."
]

]

titles is an array of each title type, with fields in a particular order. I want to read this into a more standard JSON format:

{
  'short_title': "Public Online Information Act of 2011",
  'official_title': "To establish an advisory committee to issue nonbinding governmentwide guidelines..."
}

The short title or official title may or may not be there, and there could actually be several short titles.

How do I make a Reads for this? Right now I've got:

implicit val billReads: Reads[Bill] = (
  (JsPath \ "id").read[Int] and
  (JsPath \ "display_number").read[String] and
  (JsPath \ "current_status").read[String] and
  (JsPath \ "titles")(0)(2).read[String]
  )(Bill.apply _)

How do I specify "The member of the array that has a first element equal to 'official'"?

Can you be more specific about the format? Your example isn't clear. — Ryan
– Ryan, Commented Dec 3, 2014 at 2:41

mavarazy · Accepted Answer · 2014-12-03 07:41:45Z

1

As far as I know, there is no out of the box way to do it, but I would do it with additional custom reader, like this:

val officialReads = new Reads[String] {
  override def reads(json: JsValue): JsResult[String] = (json \ "titles") match {
    case JsArray(titles) => titles.collectFirst({
      case JsArray(values) if (values.headOption.map(v => "official".equals(v.as[String])).getOrElse(false)) =>
        JsSuccess(values.tail.tail.head.as[String])
    }).getOrElse(JsError("No official title"))
    case _ => JsError("Can't read official title")
  }
}

And your Bill reader would look like this:

  val implicitReads: Reads[Bill] = (
    (__ \ "id").read[Int] and
    (__ \ "display_number").read[String] and
    (__ \ "current_status").read[String] and
    officialReads
    )(Bill.apply _)

I've tested, this works :)

answered Dec 3, 2014 at 7:41

mavarazy

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