Play Framework Json Transform recursivly

Question

since a while I am fooling around with the following problem.

I try to recursivly transform through a tree-like json structure.

{
    "id": 21,
    "title": "Title1",
    "children": [
        {
            "id": 22,
            "title": "Title1.1",
            "children": [
                {
                    "id": 33,
                    "title": "Title1.1.1",
                    "children": [
                        {
                            "id": 41,
                            "title": "Title1.1.1.1",
                            "children": [
                                {
                                    "id": 42,
                                    "title": "Title1.1.1.1.1",
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

So far I have :

  val idChanger:Reads[JsObject] = (__ \ 'id).json.update(of[JsNumber].map{case JsNumber(nb) => JsNumber(nb * 100)})

  val childPicker:Reads[JsValue] = (__ \ 'children).json.pick[JsArray].map{
    case JsArray(arr) => JsArray(arr.map(o => {
      o.transform(idChanger) match {
        case JsSuccess(value, jsPath) =>
          println(s"Success:$value")
          value
        case JsError(errors) =>
          println(s"Error:$errors"); JsNull
      }
    }))
  }

val jsvalue: JsValue = ...
jsvalue.transform(childPicker)
...

This works only on the first level and changes the id '21' accordingly, but not the rest so far.

I tried many different ways to do the rest of the children recursivly too, but no success so far.

Any help on this one would be appreciated.

Cheers, Rob.

Hi, it does not fail, but I just do not get the recursion working (In the code above there is no recursion, but this is the base I used to get the recursion somehow in). The solution might be completely different and the approach above is completely wrong, but I have no other idea. So far. — Rob

Ben Ben · Accepted Answer · 2015-04-19T19:32:18

Just add the recursive call inside your Reads and make sure to handle JsArray as well as JsObject. Here is a simple example which fits this basic idea.

val idChanger: Reads[JsObject] =
  (__ \ 'id).json.update(of[JsNumber].map{case JsNumber(nb) => JsNumber(nb * 100)})


val picker: Reads[JsValue] = __.json.pick.map{
  case JsArray(arr) => JsArray(arr.map(_.transform(picker).get))
  case v: JsValue =>
    v.transform(
      idChanger andThen (__ \ "children").json.update(picker) orElse
      idChanger
  ).get
}

Play Framework Json Transform recursivly

1 Answers