如何使用任意模式解析json，更新/创建一个字段并将其写回json(Scala)

Question

如何使用任意模式在JSON对象中更新/创建字段，并将其写入Scala中的JSON？

我试过用类似于spray-json的方法：

import spray.json._
import DefaultJsonProtocol._
val jsonAst = """{"anyfield":"1234", "sought_optional_field":5.0}""".parse
val newValue = jsonAst.asJsObject.fields.getOrElse("sought_optional_field", 1)
val newMap = jsonAst.asJsObject.fields + ("sought_optional_field" -> newValue)
JSONObject(newMap).toJson

但是它给出了奇怪的结果："{"anyfield"[ : "1234", "sought_optional_field" : ]1}

Answer 1

你差点就到了：

import spray.json._
import DefaultJsonProtocol._

def changeField(json: String) = {
  val jsonAst = JsonParser(json)
  val map = jsonAst.asJsObject.fields
  val sought = map.getOrElse("sought_optional_field", 1.toJson)
  map.updated("sought_optional_field", sought).toJson
}

val jsonA = """{"anyfield":"1234", "sought_optional_field":5.0}"""
val jsonB = """{"anyfield":"1234"}"""

changeField(jsonA)
// spray.json.JsValue = {"anyfield":"1234","sought_optional_field":5.0}
changeField(jsonB)
// spray.json.JsValue = {"anyfield":"1234","sought_optional_field":1}

使用Argonaut：

import argonaut._, Argonaut._

def changeField2(json: String) =
  json.parseOption.map( parsed =>
    parsed.withObject(o => 
      o + ("sought_optional_field", o("sought_optional_field").getOrElse(jNumber(1)))
    )
  )

changeField2(jsonA).map(_.nospaces)
// Option[String] = Some({"anyfield":"1234","sought_optional_field":5})
changeField2(jsonB).map(_.nospaces)
// Option[String] = Some({"anyfield":"1234","sought_optional_field":1})