Scala - How to implement implicit JSON reader - json

Question

I've implemented implicit Json Reads in order to read two fields from JSON, saleId and saleType. I wanted to make getSales method return a tuple (Int, String) representing saleId and saleType accordingly. But when I call the getSales method I'm getting the following errors:
Error:(46, 79) No JSON deserializer found for type (Int, String). Try to implement an implicit Reader or JsonFormat for this type.
val salesData = (salesJson \ "sales").as[(Int, String)]
Error:(46, 79) not enough arguments for method as: (implicit reader: org.json4s.Reader[(Int, String)], implicit mf: Manifest[(Int, String)])(Int, String).
Unspecified value parameters reader, mf.
val salesData = (salesJson \ "sales").as[(Int, String)]
I have implemented implicit Json Reads so really confused with the first error. Here is my implementation:
def getsales(context: SparkContext, saleId: Int): (Int, String)= {
val url= buildUrl(context, saleId)
implicit val salesReader: Reads[(Int, String)] = (
(__ \ "id_from_API").read[Int] and
(__ \ "sale_type").read[String]
).tupled
val salesJson: JValue = parse(httpStringResponse(url, context))
val salesData = (salesJson \ "sales_stats").as[(Int, String)]
salesData
}

Answer 1

Two notes concerning you code:
val salesData = (salesJson \ "sales").as[(Int, String)]
val salesData = (salesJson \ "sales_stats").as[(Int, String)]
might have to be the same.
Instead of JValue you might have wanted to put JsValue in the line
val salesJson: JValue = parse(httpStringResponse(url, context))
Other than that testing your JSON reader code separately from the rest of your code might be helpful.
The following worked for me:
import org.scalatest.WordSpec
import play.api.libs.functional.syntax._
import play.api.libs.json._
class ReadsExample extends WordSpec {
"read" in {
val sales =
"""
{
"sales_stats": {
"id_from_API": 42,
"sale_type": "cheap"
}
}
""".stripMargin
implicit val salesReader: Reads[(Int, String)] = (
(JsPath \ "id_from_API").read[Int] and
(JsPath \ "sale_type").read[String]
).tupled
val salesJson: JsValue = Json.parse(sales)
val salesData = (salesJson \ "sales_stats").as[(Int, String)]
}
}
Please note that the version of play-json used here is 2.3.10.
EDIT
code example to the question in the comment
import org.scalatest.WordSpec
import play.api.libs.json.Json.reads
import play.api.libs.json.{Json, _}
class ReadsExample extends WordSpec {
"read" in {
val sales =
"""
{
"id_from_API": 9,
"sale_type": {
"main" : "a",
"sub" : "b"
}
}
""".stripMargin
val salesJson: JsValue = Json.parse(sales)
val salesData = salesJson.as[Sales]
}
}
case class Sales(id_from_API: Int, sale_type: SaleType)
case class SaleType(main: String, sub: String)
object Sales {
implicit val st: Reads[SaleType] = reads[SaleType]
implicit val of: Reads[Sales] = reads[Sales]
}