Playframework - JSON parsing object with single field - definition issue - json

Question

I cannot find a way how to make it work when deserialized object has single field - I cannot compile the code. Seems that and operator does some transformation and I cannot find a method to call to do the same.
I have following json:
{"total": 53, "max_score": 3.2948244, "hits": [
{
"_index": "h",
"_type": "B",
"_id": "3413569628",
"_score": 3.2948244,
"_source": {
"fotky": [
{
"popisek":" ",
"localFileSystemLocation":" ",
"isMain": true,
"originalLocation": ""
}
]
}
}
]
}
I try the following data model to de serialize to:
case class SearchLikeThisResult(total: Int, max_score: Double, hits: Seq[Hits])
case class Hits(_index: String, _type: String, _id: String, _score: Double, _source: Source)
case class Source(fotky: Seq[Photo])
case class Photo(isMain: Boolean, originalLocation: Option[String], localFileSystemLocation: Option[String], popisek: Option[String])
Implicit reads as follows:
object SearchLikeThisHits {
import play.api.libs.functional.syntax._
implicit val photoReads: Reads[Photo] = (
(JsPath \ "isMain").read[Boolean] and
(JsPath \ "originalLocation").readNullable[String] and
(JsPath \ "localFileSystemLocation").readNullable[String] and
(JsPath \ "popisek").readNullable[String]
)(Photo.apply _)
implicit val sourceReads: Reads[Source] = (
(JsPath \ "fotky").read[Seq[Photo]]
)(Source.apply _)
implicit val hitsReads: Reads[Hits] = (
(JsPath \ "_index").read[String] and
(JsPath \ "_type").read[String] and
(JsPath \ "_id").read[String] and
(JsPath \ "_score").read[Double] and
(JsPath \ "_source").read[Source]
)(Hits.apply _)
implicit val searchLikeThisResult: Reads[SearchLikeThisResult] = (
(JsPath \ "total").read[Int] and
(JsPath \ "max_score").read[Double] and
(JsPath \ "hits").read[Seq[Hits]]
)(SearchLikeThisResult.apply _)
}
What I am really struggling with is under the _source:
implicit val sourceReads: Reads[Source] = (
(JsPath \ "fotky").read[Seq[Photo]]
)(Source.apply _)
where read is reported as unkown symbol - in other cases and performs some transformation.
Inline definition doesn't help either.
Does anybody faced this before?

Answer 1

The fancy applicative builder syntax (and, etc.) is nice, but it can obscure the fact that Reads is monadic and also works perfectly well with map, flatMap, for-comprehensions, etc.
So while the applicative builder syntax doesn't work with single values, plain old map does:
implicit val sourceReads: Reads[Source] =
(JsPath \ "fotky").read[Seq[Photo]].map(Source(_))
The key here is that (JsPath \ "fotky").read[Seq[Photo]] is a Reads[Seq[Photo]], and you want a Reads[Source]. map gives you a way to get from one to the other, just as you could use it to transform an Option[Seq[Photo]] into an Option[Source, for example.

Answer 2

You could save yourself some trouble by making use of the Json.reads to automatically generate your Reads (provided the case class is defined exactly like the Json objects - which is your case).
implicit val photoReads = Json.reads[Photo]
implicit val sourceReads = Json.reads[Source]
implicit val hitsReads = Json.reads[Hits]
implicit val searchResultReads = Json.reads[SearchLikeThisResult]
For more information, see https://www.playframework.com/documentation/2.1.1/ScalaJsonInception