Question

我使用json-lenses并尝试递归搜索Json对象的分支，类似于：

import spray.json._
import spray.json.lenses.JsonLenses._
import DefaultJsonProtocol._
import scala.annotation.tailrec

@tailrec
def getLens(json: JsValue, lensAcc: Lens = Nil, depth: Int = 0): Lens = {
  if (depth > 10) {
    throw new IllegalStateException("Recursive search for lens exhausted.")
  }
  val thisLens = lensAcc / 'rec / element(0)
  json.extract[JsObject](thisLens / 'properties.?) match {
    case None => getLens(json, thisLens, depth + 1)
    case _ => thisLens
  }
}

val json = """{"rec": [{"rec": [{"properties": {}}]}]}""".parseJson.asJsObject

val myLens = getLens(json)

这是不对的。我对Scala比较陌生，无法弄清楚如何解决这个问题。

Answer 1

这应该有效：

  def nextLens = 'rec / element(0)

  @scala.annotation.tailrec
  final def getLens(json: JsObject, lensAcc: Lens[Id] = nextLens, depth: Int = 0): Lens[Id] = {
    if (depth > 10) {
      throw new IllegalStateException("Recursive search for lens exhausted.")
    }
    json.extract[JsObject](lensAcc / 'properties.?) match {
      case None => getLens(json, lensAcc / nextLens, depth + 1)
      case _ => lensAcc
    }
  }

测试：

scala> val json = JsonParser("""{"rec": [{"rec": [{"properties": {}}]}]}""").asJsObject
json: spray.json.JsObject = {"rec":[{"rec":[{"properties":{}}]}]}
scala> getLens(json)
res6: spray.json.lenses.Lens[spray.json.lenses.Id] = spray.json.lenses.JsonLenses$$anon$1@448cd79c
scala> json.extract[JsObject](res6)
res9: spray.json.JsObject = {"properties":{}}

我不知道是否有空镜头......

如何递归建立一个json镜头

1 个答案: