Query and find the path of an JSON element value with Play JSON

Question

I'm using Play Framework with Scala. I have the following structure for JSON being returned by an upstream server. This is just a representation

{
  "key": "some-key",
  "suspendData": {
    "d": [
      [
        "arbitrary-objects/strings"
      ],
      [
        "random-value",
        [
          "arbitrary-objects/strings"
        ],
        [
          [
            "value1",
            "important-item",
            [
              "important-key-1"
            ],
            "arbitrary-values/objects"
          ],
          [
            "value2",
            "important-item-2",
            [
              "important-key-2"
            ]
          ]
        ]
      ]
    ]
  }
}

The only facts that I have is that the data will be located somewhere within $.suspendData.d[1]. I know the value that I am searching for which is important-key-1. The value can be nested deeper or it could be on a different index within `d[1]. How do I approach the problem of finding whether

1. The key exists in the JSON that has been obtained from the upstream server.
2. The path where the key was found, so I can find other keys based on the same path. This is a reverse lookup problem.

I can currently only think of getting $.suspendData.d[1] and then loop to find whether such properties exist. Again, I can't find a proper way of doing this via JsPath. I know the JsonPath equivalent, but can't find the right way through existing Play JSON support.

Answer 1

You can use \ method defined on JsValue and navigate to the place you want in the Json

To get what you want do ((json \ "suspendData") \ "d")(1)

Here is the REPL output for the same

scala> val json = Json.parse(str) 
json: JsValue = {"key":"some-key","suspendData":{"d":[["arbitrary-objects/strings"],["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]]}}

scala> ((json \ "suspendData") \ "d")(1) 
res32: JsLookupResult = JsDefined(
  ["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]
)

scala> val json = Json.parse(str) 
json: JsValue = {"key":"some-key","suspendData":{"d":[["arbitrary-objects/strings"],["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]]}}

scala> (json \ "suspendData") 
res34: JsLookupResult = JsDefined(
  {"d":[["arbitrary-objects/strings"],["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]]}
)

scala> (json \ "suspendData") \ "d" 
res35: JsLookupResult = JsDefined(
  [["arbitrary-objects/strings"],["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]]
)

scala> ((json \ "suspendData") \ "d")(0) 
res36: JsLookupResult = JsDefined(["arbitrary-objects/strings"])

scala> ((json \ "suspendData") \ "d")(1) 
res37: JsLookupResult = JsDefined(
  ["random-value",["arbitrary-objects/strings"],[["value1","important-item",["important-key-1"],"arbitrary-values/objects"],["value2","important-item-2",["important-key-2"]]]]
)

Answer 2

Simple recursion, may be not so effective, but worked:

def findPath(key: String, path: JsPath, xs: JsValue): Option[JsPath] = {
  xs match {
    case o:JsObject =>
      var res: Option[JsPath] = None
      val it = o.fields.iterator
      while (res.isEmpty && it.hasNext) {
        val e = it.next()
        res = findPath(key, path \ (e._1), e._2)
      }
      res
    case JsString(x) if x==key => 
      Some(path)
    case JsArray(x) =>
      var res: Option[JsPath] = None
      val it = x.zipWithIndex.iterator
      while (res.isEmpty && it.hasNext) {
        val e = it.next()
        res = findPath(key, path(e._2), e._1)
      }
      res
    case _ => None
  }
}

findPath("important-key-1", __, j)
findPath("important-key-2", __, j)
findPath("important-key-3", __, j)
findPath("some-key", __, j)

scala> res62: Option[play.api.libs.json.JsPath] = Some(/suspendData/d(1)(2)(0)(2)(0))

scala> res63: Option[play.api.libs.json.JsPath] = Some(/suspendData/d(1)(2)(1)(2)(0))

scala> res64: Option[play.api.libs.json.JsPath] = None

scala> res65: Option[play.api.libs.json.JsPath] = Some(/key)