Question

我正在阅读https://www.playframework.com/documentation/2.0.4/ScalaJsonGenerics

SearchResult[T]示例正是我想要的，但是我在编译时遇到了错误：

导入play.api.libs.json ._

case class SearchResults[T](
                             elements: List[T],
                             page: Int,
                             pageSize: Int,
                             total :Int
                           )
object SearchResults
{
  implicit def searchResultsReads[T](implicit fmt: Reads[T]): Reads[SearchResults[T]] = new Reads[SearchResults[T]] {
    def reads(json: JsValue): SearchResults[T] = new SearchResults[T] (

      (json \ "elements") match {
        case JsArray(ts) => ts.map(t => Json.fromJson(t)(fmt))
        case _ => throw new RuntimeException("Elements MUST be a list")
      },
      (json \ "page").as[Int],
      (json \ "pageSize").as[Int],
      (json \ "total").as[Int]
    )
  }

  implicit def searchResultsWrites[T](implicit fmt: Writes[T]): Writes[SearchResults[T]] = new Writes[SearchResults[T]] {
    def writes(ts: SearchResults[T]) = JsObject(Seq(
      "page" -> JsNumber(ts.page),
      "pageSize" -> JsNumber(ts.pageSize),
      "total" -> JsNumber(ts.total),
      "elements" -> JsArray(ts.elements.map(Json.toJson(_)))
    ))
  }
}

我有以下编译错误：

Error:(17, 14) constructor cannot be instantiated to expected type;
 found   : play.api.libs.json.JsArray
 required: play.api.libs.json.JsLookupResult
        case JsArray(ts) => ts.map(t => Json.fromJson(t)(fmt))

Answer 1

方法fromJson和toJson是在类中定义的方法：

play.api.libs.json.Json

带有play json的case类泛型

1 个答案: