playframework - how to update json's indexed array item

Question

I am having a problem with adding an json object into an array item. This problem has been troubling me for quite some time but I still have no clue how to fix it.

I want to add a json object in an array item, below is the existing json object:

{
  "key1":[ 
          {"key11":"value11"},
          {"key12":"value12"}
         ]
}

I want it be transformed with a new json object added :

{
   "key1":[ 
           {"key11":"value11" , "key111":"value111"},
           {"key12":"value12"}
         ]
}

Here is my code :

val json = Json.obj( 
         "key1" ->Json.arr(
                        Json.obj("key11" -> "value11"),
                        Json.obj("key12" -> "value12")
         )
)

val transform= (__ \ 'key1 )(0).json.update(  __.read[JsObject].map{ o => o ++ Json.obj( "key111" -> "value111" ) } )

json.validate(transform)

But the last line gives below exceptions. Is there anyone can give me suggestions on how to achieve my goal of adding an json object into an array item ?

java.lang.RuntimeException: expected KeyPathNode
at play.api.libs.json.JsPath$.step$1(JsPath.scala:141)
at play.api.libs.json.JsPath$.step$1(JsPath.scala:144)
at play.api.libs.json.JsPath$.play$api$libs$json$JsPath$$buildSubPath$1(JsPath.scala:150)
at play.api.libs.json.JsPath$$anonfun$createObj$1.apply(JsPath.scala:155)
at play.api.libs.json.JsPath$$anonfun$createObj$1.apply(JsPath.scala:153)
at scala.collection.IndexedSeqOptimized$class.foldl(IndexedSeqOptimized.scala:51)
at scala.collection.IndexedSeqOptimized$class.foldLeft(IndexedSeqOptimized.scala:60)
at scala.collection.mutable.WrappedArray.foldLeft(WrappedArray.scala:34)
at play.api.libs.json.JsPath$.createObj(JsPath.scala:153)
at play.api.libs.json.PathReads$$anonfun$jsUpdate$1$$anonfun$apply$15.apply(JsConstraints.scala:81)
at play.api.libs.json.PathReads$$anonfun$jsUpdate$1$$anonfun$apply$15.apply(JsConstraints.scala:81)
at play.api.libs.json.JsResult$class.map(JsResult.scala:73)

Thanks for listening

Cyril

Answer 1

You need to select the whole array and transform that into a new array like this:

val transform= (__ \ "key1" ).json.update(
  __.read[JsArray].map { a => 
    JsArray(a.value.updated(0, a(0).as[JsObject] ++ Json.obj("key111" -> "value111")))
  }
)