Question

我正在使用implicit val reads映射Json，如：

{
   "id": 1
   "friends": [
    {
      "id": 1,
      "since": ...
    },
    {
      "id": 2,
      "since": ...
    },
    {
      "id": 3,
      "since": ...
    }
  ]
}

到案例类

case class Response(id: Long, friend_ids: Seq[Long])

我只能使用反映JSON friends结构的中间类。但我从来没有在我的应用程序中使用它。有没有办法编写Reads[Response]对象，以便我的Response类直接映射到给定的JSON？

Answer 1

您只需要对Reads.seq()使用明确的friend_ids进行简单的阅读[回复]，例如

val r: Reads[Response] = (
  (__ \ "id").read[Long] and
    (__ \ "friends").read[Seq[Long]](Reads.seq((__ \ "id").read[Long]))
  )(Response.apply _)

结果将是：

r.reads(json)

scala> res2: play.api.libs.json.JsResult[Response] = JsSuccess(Response(1,List(1, 2, 3)),)

Answer 2

您可以尝试以下

@annotation.tailrec
def go(json: Seq[JsValue], parsed: Seq[Long]): JsResult[Seq[Long]] =
  json.headOption match {
    case Some(o @ JsObject(_)) => (o \ "id").validate[Long] match {
      case JsError(cause) => JsError(cause)
      case JsSuccess(id)  => go(json.tail, parsed :+ id)
    }
    case Some(js) => JsError(s"invalid friend JSON (expected JsObject): $js")
    case _ => JsSuccess(parsed) // nothing more to read (success)
  }

implicit val friendIdReader = Reads[Seq[Long]] {
  case JsArray(values) => go(values, Nil)
  case json => JsError(s"unexpected JSON: $json")
}

implicit val responseReader = Json.reads[Response]
// responseReader will use friendIdReader as Reads[Seq[Long]],
// for the property friend_ids

Answer 3

简单的方法可能是：

import play.api.libs.functional.syntax._
import play.api.libs.json.{JsValue, Json, _}


case class Response(id: Long, friend_ids: Seq[Friends])

object Response {

  implicit val userReads: Reads[Response] = (
    (JsPath \ "id").read[Long] and
      (JsPath \ "friends").read[Seq[Friends]]
    ) (Response.apply _)
}

case class Friends(id: Long, since: String)
object Friends {
  implicit val fmt = Json.format[Friends]
}

没有case class Friends我发现难以找到解决方案，但如果我找到一个解决方案就会发布

编辑：添加了关于Scala reedit的答案链接

所以，我想更多地了解如何将json解析为模型，并决定询问Reedit。收到一些非常酷的链接，看看：

https://www.reddit.com/r/scala/comments/4bz89a/how_to_correctly_parse_json_to_scala_case_class/

scala play读取解析嵌套的json

3 个答案: