如何在spray-json中表示可选字段？

Question

我的请求中有一个可选字段:

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

我的协议是:

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

如何将nextAt字段标记为可选,以便正确读取和接受以下JSON对象:

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

我实际上并不关心null的情况,但如果你有细节,那就太好了.我正在使用spray-json,并且认为如果原始JSON对象上没有该选项,则使用Option会跳过该字段.

Answer 1

适合我(喷-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")))
}

Answer 2

您可能必须创建显式格式(警告: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)))
        }
    }
}

Answer 3

使用NullOptionstrait禁用跳过nulls:https: //github.com/spray/spray-json#nulloptions 示例:https: //github.com/spray/spray-json/blob/master/src/test/scala/spray/ JSON/ProductFormatsSpec.scala