Spray-json deserializing nested object - json

Question

How to deserialize nested objects correctly in spray-json?
import spray.json._
case class Person(name: String)
case class Color(n: String, r: Int, g: Int, b: Int, p: Person)
object MyJsonProtocol extends DefaultJsonProtocol {
implicit object ColorJsonFormat extends RootJsonFormat[Color] {
def write(c: Color) = JsObject(
"color-name" -> JsString(c.n),
"Green" -> JsNumber(c.g),
"Red" -> JsNumber(c.r),
"Blue" -> JsNumber(c.b),
"person-field" -> JsObject("p-name" -> JsString(c.p.name))
)
def read(value: JsValue) = {
value.asJsObject.getFields("color-name", "Red", "Green", "Blue", "person-field") match {
case Seq(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue), JsObject(person)) =>
Color(name, red.toInt, green.toInt, blue.toInt, null) //gotta replace null with correct deserializer
case _ => throw new DeserializationException("Color expected")
}
}
}
}
import MyJsonProtocol._
val jsValue = Color("CadetBlue", 95, 158, 160, Person("guest")).toJson
jsValue.prettyPrint
val color = jsValue.convertTo[Color] //person is missing of course
On a side-note, how to spray-json help serializing to a map of fields (with nested map for nested objects)?

Answer 1

The example below demonstrates JSON -> Abstract Syntax Tree -> Scala Case Classes and back with custom field names and support for optional case class members. The example is derived from the spray-json documentation at https://github.com/spray/spray-json for version 1.2.5.
package rando
import spray.json._
case class Color(name: String, red: Int, green: Int, blue: Int)
case class Team(name: String, color: Option[Color])
object MyJsonProtocol extends DefaultJsonProtocol {
implicit val colorFormat = jsonFormat(Color, "name", "r", "g", "b")
implicit val teamFormat = jsonFormat(Team, "name", "jersey")
}
import MyJsonProtocol._
object GoSox extends App {
val obj = Team("Red Sox", Some(Color("Red", 255, 0, 0)))
val ast = obj.toJson
println(obj)
println(ast.prettyPrint)
println(ast.convertTo[Team])
println("""{ "name": "Red Sox", "jersey": null }""".asJson.convertTo[Team])
println("""{ "name": "Red Sox" }""".asJson.convertTo[Team])
}
The example outputs the following when executed:
Team(Red Sox,Some(Color(Red,255,0,0)))
{
"name": "Red Sox",
"jersey": {
"name": "Red",
"r": 255,
"g": 0,
"b": 0
}
}
Team(Red Sox,Some(Color(Red,255,0,0)))
Team(Red Sox,None)
Team(Red Sox,None)

Answer 2

To your remaining question - how to reuse JSON conversions within a wrapping type:
"person-field" -> JsObject("p-name" -> JsString(c.p.name))
I would change this to:
"person-field" -> p.toJson
This way, you are letting the Person case class JSONify itself, instead of introducing another way in the wrapping object. DRY and simpler.
And:
case Seq(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue), JsObject(person)) =>
Color(name, red.toInt, green.toInt, blue.toInt, null)
Use the .convertTo[Person] here:
case Seq(JsString(name), JsNumber(red), JsNumber(green), JsNumber(blue), jsv) =>
Color(name, red.toInt, green.toInt, blue.toInt, jsv.convertTo[Person])
If there are problems, please ask for more help. I have similar structure in my own project but didn't try to run them in this context.

Answer 3

import models.{Address, Patient}
import spray.json._
object Hospital {
object MyJsonProtocol extends DefaultJsonProtocol {
implicit val address = jsonFormat(Address, "country", "state", "zip")
implicit val patient = jsonFormat(Patient, "name", "regNumber", "address")
}
import MyJsonProtocol._
def main(args: Array[String]): Unit = {
val p1 = Patient(name = "Amar", regNumber = 234, address = Address("IN", "KA", 49))
println(p1.toJson.sortedPrint)
}
}
Output
{
"address": {
"country": "IN",
"state": "KA",
"zip": 49
},
"name": "Amar",
"regNumber": 234
}