How to use different names when mapping JSON array to Scala object using combinators

Question

Given a JSON array like this one:

{
    "success": true,
    "data": [
        {
            "id": 600,
            "title": "test deal",
            "e54cbe3a434d8e6": 54
        },
        {
            "id": 600,
            "title": "test deal",
            "e54cbe3a434d8e6": 54
        },
    ],
    "additional_data": {
        "pagination": {
            "start": 0,
            "limit": 100,
            "more_items_in_collection": false
        }
    }
}

In my Play 2.2.2 application, using the Scala JSON Reads Combinator, everything works going this way:

implicit val entityReader = Json.reads[Entity]

  val futureJson: Future[List[Entity]] = futureResponse.map(
    response => (response.json \ "data").validate[List[Entity]].get

The problem now is the key named 'e54cbe3a434d8e6' which I would like to name 'value' in my object:

// This doesn't work, as one might expect
case class Entity(id: Long, title: String, e54cbe3a434d8e6: Long)

// I would like to use 'value' instead of 'e54cbe3a434d8e6'
case class Entity(id: Long, title: String, value: Long)

There is vast information about the combinators here and here but I only want to use a fieldname which is different from the key name in the JSON array. Can some one help me to find a simple way? I suppose it has got something to do with JSON.writes?!

Andrey Neverov · Accepted Answer · 2014-04-10 16:52:52Z

One simple way without trying to apply transformations on json itself is to define a custom Reads in such a way to handle this:

val json = obj(
  "data" -> obj(
    "id" -> 600, 
    "title" -> "test deal", 
    "e54cbe3a434d8e6" -> 54))

case class Data(id: Long, title: String, value: Int)

val reads = (
  (__ \ "id").read[Long] ~
  (__ \ "title").read[String] ~
  (__ \ "e54cbe3a434d8e6").read[Int] // here you get mapping from your json to Scala case class
)(Data) 

def index = Action {
  val res = (json \ "data").validate(reads)
  println(res) // prints "JsSuccess(Data(600,test deal,54),)"
  Ok(json)
}

Another way is to use combinators like this:

... the same json and case class

implicit val generatedReads = reads[Data]

def index = Action {

  val res = (json \ "data").validate(
    // here we pick value at 'e54cbe3a434d8e6' and put into brand new 'value' branch
    __.json.update((__ \ "value").json.copyFrom((__ \ "e54cbe3a434d8e6").json.pick)) andThen 

    // here we remove 'e54cbe3a434d8e6' branch
    (__ \ "e54cbe3a434d8e6").json.prune andThen 

    // here we validate result with generated reads for our case class
    generatedReads) 

  println(res) // prints "JsSuccess(Data(600,test deal,54),/e54cbe3a434d8e6/e54cbe3a434d8e6)"
  Ok(prettyPrint(json))
}

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