json - Play Json 读取和字符串

Question

我在 Play 2.3 中有以下 JSON 阅读器:

import play.api.libs.json._
import play.api.libs.json.Reads._
val airportSearchReads: Reads[String] = (JsPath \ "search").read[String](minLength(3))

编译器给了我错误

diverging implicit expansion for type play.api.libs.json.Reads[M]
starting with method ArrayReads in trait DefaultReads

如果我使用 implicit val我得到

 ambiguous implicit values:
 both value uuidReads in trait DefaultReads of type => play.api.libs.json.Reads[java.util.UUID]
 and value airportSearchReads in object AirportSearch of type => play.api.libs.json.Reads[String]
 match expected type play.api.libs.json.Reads[M]

我如何让它工作？

Answer 1

我得到一个不同的错误，但如果我向 minLength 添加一个显式类型参数，它对我来说很好用:

scala> val airportSearchReads: Reads[String] = (JsPath \ "search").read[String](minLength[String](3))
airportSearchReads: play.api.libs.json.Reads[String] = play.api.libs.json.Reads$$anon$8@3fee86da

我认为将其留给编译器的问题在于，作用域中有不同的隐式组合可以满足 minLength 的隐式参数列表。 .