How to filter JSON array results based on condition?

Question

I'm using Scala Play 2.7.2 and have read ScalaJsonTransformers and ScalaJson. After calling a JSON API I get back (simplified MCVE) results like this:

{
  "type": "searchset",
  "total": 5,
  "entry": [
    {
        "start": "2019-06-07T09:00:00",
        "end": "2019-06-07T11:00:00",
        "id": "55"
    },
    {
        "start": "2019-06-07T13:00:00",
        "end": "2019-06-07T15:00:00",
        "id": "56"
    },
    {
        "start": "2019-06-07T16:00:00",
        "end": "2019-06-07T17:00:00",
        "id": "60"
    },
    {
        "start": "2019-06-10T11:00:00",
        "end": "2019-06-10T12:00:00",
        "id": "58"
    },
    {
        "start": "2019-06-11T14:00:00",
        "end": "2019-06-11T15:00:00",
        "id": "61"
    }
  ]
}

and I'd like to filter the results and choose only the ones that satisfy a condition, for example, filter out the ones whose end date is greater than certain date val to = new DateTime("2019-06-10T00:00:00") and doing something alla:

(json \\ "end").filter(new DateTime(_).isBefore(to.toDate.getTime))...

but this doesn't work because the result is the selection and not the entire json node and besides it leaves the outer part too.

The solution should output the result:

{
  "type": "searchset",
  "total": 3,
  "entry": [
    {
        "start": "2019-06-07T09:00:00",
        "end": "2019-06-07T11:00:00",
        "id": "55"
    },
    {
        "start": "2019-06-07T13:00:00",
        "end": "2019-06-07T15:00:00",
        "id": "56"
    },
    {
        "start": "2019-06-07T16:00:00",
        "end": "2019-06-07T17:00:00",
        "id": "60"
    }
}

How can this be done using Play JSON?

Answer 1

For coast-to-coast design try defining update transformer like so

val to = new DateTime("2019-06-10T00:00:00")

val endDateFilterTransformer = (__ \ 'entry).json.update(__.read[JsArray].map {
  case JsArray(values) => JsArray(values.filter(v => (v \ "end").as[DateTime].isBefore(to)))
})

val outJson = json.transform(endDateFilterTransformer)
println(outJson.get)

which outputs

{
  "entry": [
    {
      "start": "2019-06-07T09:00:00",
      "end": "2019-06-07T11:00:00",
      "id": "55"
    },
    {
      "start": "2019-06-07T13:00:00",
      "end": "2019-06-07T15:00:00",
      "id": "56"
    },
    {
      "start": "2019-06-07T16:00:00",
      "end": "2019-06-07T17:00:00",
      "id": "60"
    }
  ],
  "total": 5,
  "type": "searchset"
}

Alternatively for JSON to OO design try deserialising to a model

case class Entry(start: DateTime, end: DateTime, id: String)
object Entry {
  implicit val format = Json.format[Entry]
}
case class Record(`type`: String, total: Int, entry: List[Entry])

object Record {
  implicit val format = Json.format[Record]
}

then filter using regular Scala methods

val to = new DateTime("2019-06-10T00:00:00")
val record = Json.parse(raw).as[Record]
val filteredRecord = record.copy(entry = record.entry.filter(_.end.isBefore(to)))

then deserialise back to json like so:

Json.toJson(filteredRecord)

which outputs

{
  "type": "searchset",
  "total": 5,
  "entry": [
    {
      "start": "2019-06-07T09:00:00.000+01:00",
      "end": "2019-06-07T11:00:00.000+01:00",
      "id": "55"
    },
    {
      "start": "2019-06-07T13:00:00.000+01:00",
      "end": "2019-06-07T15:00:00.000+01:00",
      "id": "56"
    },
    {
      "start": "2019-06-07T16:00:00.000+01:00",
      "end": "2019-06-07T17:00:00.000+01:00",
      "id": "60"
    }
  ]
}

where we use play-json-joda for DateTime serialisation

libraryDependencies += "com.typesafe.play" %% "play-json-joda" % "2.7.3"
import play.api.libs.json.JodaWrites._
import play.api.libs.json.JodaReads._