Scala play JSON, lookup and match defined field holding null value - json

Question

I have the following Json block that I have returned as a JsObject
{
"first_block": [
{
"name": "demo",
"description": "first demo description"
}
],
"second_block": [
{
"name": "second_demo",
"description": "second demo description",
"nested_second": [
{
"name": "bob",
"value": null
},
{
"name": "john",
"value": null
}
]
}
]
}
From this, I want to return a list of all the possible values I could have in the second block, nested array for name and value. so with the example above
List([bob,null],[john,null]) or something along those lines.
The issue I am having is with the value section understanding null values. I've tried to match against it and return a string "null" but I can't get it to match on Null values.
What would be the best way for me to return back the name and values in the nested_second array.
I've tried using case classes and readAsNullable with no luck, and my latest attempt has gone along these lines:
val secondBlock = (jsObj \ "second_block").as[List[JsValue]]
secondBlock.foreach(nested_block => {
val nestedBlock = (nested_block \ "nested_second").as[List[JsValue]]
nestedBlock.foreach(value => {
val name = (value \ "name").as[String] //always a string
var convertedValue = ""
val replacement_value = value \ "value"
replacement_value match {
case JsDefined(null) => convertedValue = "null"
case _ => convertedValue = replacement_value.as[String]
}
println(name)
println(convertedValue)
})
}
)
It seems convertedValue returns as 'JsDefined(null)' regardless and I'm sure the way I'm doing it is horrifically bad.

Answer 1

Replace JsDefined(null) with JsDefined(JsNull).
You probably got confused, because println(JsDefined(JsNull)) prints as JsDefined(null). But that is not, how null value of a JSON field is represented. null is represented as case object JsNull. This is just a good API design, where possible cases are represented with a hierarchy of classes:

Answer 2

With play-json I use always case-classes!
I simplified your problem to the essence:
import play.api.libs.json._
val jsonStr = """[
{
"name": "bob",
"value": null
},
{
"name": "john",
"value": "aValue"
},
{
"name": "john",
"value": null
}
]"""
Define a case class
case class Element(name: String, value: Option[String])
Add a formatter in the companion object:
object Element {
implicit val jsonFormat: Format[Element] = Json.format[Element]
}
An use validate:
Json.parse(jsonStr).validate[Seq[Element]] match {
case JsSuccess(elems, _) => println(elems)
case other => println(s"Handle exception $other")
}
This returns: List(Element(bob,None), Element(john,Some(aValue)), Element(john,None))
Now you can do whatever you want with the values.