How to represent optional fields in spray-json?

Question

I have an optional field on my requests:

case class SearchRequest(url: String, nextAt: Option[Date])

My protocol is:

object SearchRequestJsonProtocol extends DefaultJsonProtocol {
    implicit val searchRequestFormat = jsonFormat(SearchRequest, "url", "nextAt")
}

How do I mark the nextAt field optional, such that the following JSON objects will be correctly read and accepted:

{"url":"..."}
{"url":"...", "nextAt":null}
{"url":"...", "nextAt":"2012-05-30T15:23Z"}

I actually don't really care about the null case, but if you have details, it would be nice. I'm using spray-json, and was under the impression that using an Option would skip the field if it was absent on the original JSON object.

score 28 · Answer 1 · answered May 30 '12 at 18:06

Works for me (spray-json 1.1.1 scala 2.9.1 build)

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

// string instead of date for simplicity
case class SearchRequest(url: String, nextAt: Option[String])

// btw, you could use jsonFormat2 method here
implicit val searchRequestFormat = jsonFormat(SearchRequest, "url", "nextAt")

assert {
  List(
    """{"url":"..."}""",
    """{"url":"...", "nextAt":null}""",
    """{"url":"...", "nextAt":"2012-05-30T15:23Z"}""")
  .map(_.asJson.convertTo[SearchRequest]) == List(
    SearchRequest("...", None),
    SearchRequest("...", None),
    SearchRequest("...", Some("2012-05-30T15:23Z")))
}

Ah, I'm using spray-json 1.0.0, Scala 2.9.0.1. I want to upgrade soonish, but I'm not there. yet. Thanks for your answer! — François Beausoleil, May 31 '12 at 18:40

score 11 · Accepted Answer · edited May 30 '12 at 16:41

You might have to create an explicit format (warning: psuedocodish):

object SearchRequestJsonProtocol extends DefaultJsonProtocol {
    implicit object SearchRequestJsonFormat extends JsonFormat[SearchRequest] {
        def read(value: JsValue) = value match {
            case JsObject(List(
                    JsField("url", JsString(url)),
                    JsField("nextAt", JsString(nextAt)))) =>
                SearchRequest(url, Some(new Instant(nextAt)))

            case JsObject(List(JsField("url", JsString(url)))) =>
                SearchRequest(url, None)

            case _ =>
                throw new DeserializationException("SearchRequest expected")
        }

        def write(obj: SearchRequest) = obj.nextAt match {
            case Some(nextAt) => 
                JsObject(JsField("url", JsString(obj.url)),
                         JsField("nextAt", JsString(nextAt.toString)))
            case None => JsObject(JsField("url", JsString(obj.url)))
        }
    }
}

score 6 · Answer 3 · answered Apr 22 '14 at 15:44

6

Use NullOptions trait to disable skipping nulls: https://github.com/spray/spray-json#nulloptions Example: https://github.com/spray/spray-json/blob/master/src/test/scala/spray/json/ProductFormatsSpec.scala

answered Apr 22 '14 at 15:44

Alex Abdugafarov

6,112
7
35
59

score 0 · Answer 4 · answered Apr 23 '14 at 11:30

0

Don't know if this will help you but you can give that field a default value in the case class definition, so if the field is not in the json, it will assign the default value to it.

answered Apr 23 '14 at 11:30

Mohammad Qandeel

585
4
11

1

That didn't work for me ... do you need to configure anything? – samthebest Nov 30 '14 at 16:59

score 0 · Answer 5 · answered Jun 08 '18 at 08:07

Easy.

import cc.spray.json._
trait MyJsonProtocol extends DefaultJsonProtocol {
  implicit val searchFormat = new JsonWriter[SearchRequest] {
    def write(r: SearchRequest): JsValue = {
      JsObject(
        "url" -> JsString(r.url),
        "next_at" -> r.nextAt.toJson,
      )
    }
  }
}

class JsonTest extends FunSuite with MyJsonProtocol {
test("JSON") {
    val search = new SearchRequest("www.site.ru", None)
    val marshalled = search.toJson
    println(marshalled)
  }
}

smohan123 · Answer 6 · 2019-02-22T22:46:46.707

0

For anyone who is chancing upon this post and wants an update to François Beausoleil's answer for newer versions of Spray (circa 2015+?), JsField is deprecated as a public member of JsValue; you should simply supply a list of tuples instead of JsFields. Their answer is spot-on, though.

edited Feb 22 '19 at 22:46

answered Feb 22 '19 at 22:39

smohan123

1
3

How to represent optional fields in spray-json?

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