convert json to array of scala objects using spray json

Question

I am not much familier with spray json, but I have to convert the below json into Array[myTest]

Below is the code, but it doesnt work. It throws the following errors: How do I fix them?

Error:(19, 54) Cannot find JsonReader or JsonFormat type class for Array[A$A61.this.myTest]
lazy val converted= trainingDataRef.toJson.convertTo[Array[myTest]]
                                                    ^
Error:(19, 54) not enough arguments for method convertTo: (implicit evidence$1: spray.json.JsonReader[Array[A$A61.this.myTest]])Array[A$A61.this.myTest].
Unspecified value parameter evidence$1.
lazy val converted= trainingDataRef.toJson.convertTo[Array[myTest]]
                                                    ^
Error:(10, 61) could not find implicit value for evidence parameter of type spray.json.DefaultJsonProtocol.JF[Map[String,Any]]
  implicit val format: RootJsonFormat[myTest] = jsonFormat3(myTest.apply)


                                          ^


   Code:                           ^
import spray.json.DefaultJsonProtocol._
import spray.json._

case class myTest (
                        id: String,
                        classDetails: Map[String, Any],
                        school: Map[String, Any])
object myTest {
  implicit val format: RootJsonFormat[myTest] = jsonFormat3(myTest.apply)
}


val trainingDataRef = """[{"id":"my-id","classDetails":{"sec":"2","teacher":"John"},"school":{"name":"newschool"}}]"""

println(trainingDataRef.getClass)


val converted= trainingDataRef.toJson.convertTo[Array[myTest]]
println(converted)

ok, that can be changed , what would be the feasible way? Instead of Map[String, Any], should I use JsonNode? — Pratap D
– Pratap D, Commented Nov 28, 2017 at 16:05

Artavazd Balayan · Accepted Answer · 2017-11-28 17:28:18Z

1

spray-json has good documentation, try take a look there. Basically, you have to define your case classes and implement JsonFormat for them:

import spray.json.DefaultJsonProtocol._
import spray.json._

case class ClassDetails(sec: String, teacher: String)
object ClassDetails {
  implicit val format: RootJsonFormat[ClassDetails] = jsonFormat2(ClassDetails.apply)
}

case class School(name: String)
object School {
  implicit val format: RootJsonFormat[School] = jsonFormat1(School.apply)
}

case class ClassInfo
(
  id: String,
  classDetails: ClassDetails,
  school: School
)

object ClassInfo {
  implicit object ClassInfoFormat extends RootJsonFormat[ClassInfo] {
    def write(c: ClassInfo): JsValue = JsObject(
      "id" -> JsString(c.id),
      "classDetails" -> c.classDetails.toJson,
      "school" -> c.school.toJson
    )
    def read(value: JsValue): ClassInfo = {
      value.asJsObject.getFields("id", "classDetails", "school") match {
        case Seq(JsString(name), details, school) =>
          new ClassInfo(name, details.convertTo[ClassDetails], school.convertTo[School])
        case _ => throw new DeserializationException("ClassInfo expected")
      }
    }
  }
}

val json = """[{"id":"my-id","classDetails":{"sec":"2","teacher":"John"},"school":{"name":"newschool"}}]"""
// JSON string to case classes
val classInfos = json.parseJson.convertTo[Seq[ClassInfo]]
classInfos.zipWithIndex.foreach { case (c, idx) =>
  println(s"$idx => $c")
}
println
// Seq[ClassInfo] to JSON
println(s"$classInfos: ")
println(classInfos.toJson.prettyPrint)

answered Nov 28, 2017 at 17:28

Artavazd Balayan

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6 Comments

Pratap D Over a year ago

Thank you very much, its help ful . But why in my case I'm getting some additional fields and values appended to the json EX:

Pratap D Over a year ago

[ { "id": "my-id", "classDetails": { "fields": { "sec": { "value": "2" }, "teacher": { "value": "John" } } }, "school": { "fields": { "name": { "value": "newschool" } } } } ]

Artavazd Balayan Over a year ago

Have you changed something? Because I don't see any additional fields. Here is my output: pastebin.com/1NwK2Vak. I'm using spray-json 1.3.3

Pratap D Over a year ago

I have to send this to another caller, there the json is changed as above.In that application, they receive the json and copy it to another case class using as[] , but that case class is similar to the above. I don't have control on that, I should only send proper input

Pratap D Over a year ago

btw, I have changed the case class as shown below:case class ClassInfo ( id: String, classDetails: JsValue, school: JsValue )

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