[json4s]:Extracting Array of different objects - scala

Question

I am using the facebook graph API and the responses look similar to this:
{
"data": [
{
"id": "311620272349920_311718615673419",
"from": {
"id": "1456046457993048",
"name": "Richard Ettinson"
},
"to": {
"data": [
{
"id": "311620272349920",
"name": "Barbara Fallerman"
}
]
},
"with_tags": {
"data": [
{
"id": "311620272349920",
"name": "Barbara Fallerman"
}
]
},
"message": "I was gong out with her",
"actions": [
{
"name": "Comment",
"link": "https://www.facebook.com/311620272349920/posts/311718615673419"
},
{
"name": "Like",
"link": "https://www.facebook.com/311620272349920/posts/311718615673419"
}
]
}
I managed to for example extract the from field through
val extracted = (json \ "data" \"from").extract[PostFrom]
But I worry that if I use this technique I will need to pass over the Json multiple times to extract all the values I need which could lead to a bad performance.
How exactly could I extract these fields into case classes from the array of non similar objects?
I tried with the following case classes:
abstract class BaseResponse()
case class Data(list:List[Post])
case class Post(id: String, post: PostFrom) extends BaseResponse
case class PostFrom(id: String, name:String)
Which always lead to an empty List, is there a way to get back a Data class which has a list of certain classes which I am interested in? (As example the top level id, from and with_tags)

Answer 1

A possibility I found was to use more case classes instead of inheritance:
case class Root[T](data:Option[T])
case class Post(id: String, from: From, message: String)
case class From(id: String, name:String)
Basically there has to be a root object which takes some kind of graphs response object, additionally it is optional so that it won't throw an exception if there was a problem with the parsing of the response.
I then used it in the following way:
val body = r.entity.asString
val json = parse(r.entity.asString)
val root = json.extract[Root[Post]]
root.data match {
case Some(post) =>
val tagger = Tagger(post.from.id, post.from.name, post.id, post.message)
log.info(s"We received $tagger")
originalSender ! RetrievedTagger(tagger)
case None => originalSender ! NoTaggerFound
}