我有一个值类,它接受一个 Either
。我想为它生成适用于 Play for Scala v2.5.6 的 JSON Format
:
import org.joda.time.{DateTime, Duration}
case class When(when: Either[DateTime, Duration]) extends AnyVal
我认为我已经掌握了writes
方法;我遇到的问题在于reads
方法。我尝试了两种不同的方法,但都失败了。
尝试 #1,展示了reads
和writes
两个方法:
import play.api.libs.json._
import play.api.libs.json.Json.obj
object When {
def apply(dateTime: DateTime): When = When(Left(dateTime))
def apply(duration: Duration): When = When(Right(duration))
implicit val whenFormat = new Format[When] {
def reads(json: JsValue): JsResult[When] = {
val reads = (__ \ "dateTime").read[Long] { (millis: Long) =>
When(Left(new DateTime(millis)))
} | (__ \ "duration").read[Long] { (millis: Long) =>
When(Right(new Duration(millis)))
}
reads.reads(json)
}
def writes(o: When): JsValue = obj(
o.when.fold(
duration => "duration" -> duration.getMillis,
dateTime => "dateTime" -> dateTime.getMillis
)
)
}
}
错误信息如下:
overloaded method value read with alternatives:
[error] (t: Long)play.api.libs.json.Reads[Long] <and>
[error] (implicit r: play.api.libs.json.Reads[Long])play.api.libs.json.Reads[Long]
[error] cannot be applied to (Long => When)
[error] val reads = (__ \ "dateTime").read[Long] { (millis: Long) =>
[error] overloaded method value read with alternatives:
[error] (t: Long)play.api.libs.json.Reads[Long] <and>
[error] (implicit r: play.api.libs.json.Reads[Long])play.api.libs.json.Reads[Long]
[error] cannot be applied to (Long => When)
[error] } | (__ \ "duration").read[Long] { (millis: Long) =>
尝试 #2,仅展示
reads
方法:def reads(json: JsValue): JsResult[When] =
JsSuccess(
When(Left(new DateTime((__ \ "dateTime").read[Long]))) ||
When(Right(new Duration((__ \ "duration").read[Long])))
)
错误信息如下:
value || is not a member of When
[error] Note: implicit value whenFormat is not applicable here because it comes after the application point and it lacks an explicit result type
[error] Error occurred in an application involving default arguments.
我只想要一个能够工作的方法,不在意使用哪种方法(即使是我没有展示的方法),只要它是可维护且高效的。如果能知道每种方法的问题所在也会很有帮助。
extends AnyVal
对于任何一种方法都没有产生影响。 - Mike Slinn