JSON使用Play框架（Scala）中的硬編碼值讀取

Question

我想在JSON隱式讀取中使用硬編碼值，例如：

implicit val locationReads: Reads[Location] = (
  "I am a hardcoded value" and // something like that
  (JsPath \ "lat").read[Double] and
  (JsPath \ "long").read[Double]
)(Location.apply _)

有誰知道如何做到這一點？

Answer 1

使用Reads.pure產生Reads能產生一個恆定值。

implicit val locationReads: Reads[Location] = (
  Reads.pure("I am a hardcoded value") and
  (JsPath \ "lat").read[Double] and
  (JsPath \ "long").read[Double]
)(Location.apply _)

Answer 2

您可以使用自定義函數而不是Location.apply ：

case class Location(s: String, lat: Double, lon: Double)
object Location {
  implicit val locationReads: Reads[Location] = (
      (JsPath \ "lat").read[Double] and
      (JsPath \ "long").read[Double]
    )((lat, lon) => Location("I am a hardcoded value", lat, lon))
}