如何写入读取 Scala Play 的功能

Question

我在读取时遇到问题。我有这样的功能：

  private val myFunc: Reads[Foo] =
    (__  "foo")
      .readNullable[Foo]
      .map {
        case Some(foo) => foo
        case None =>
          (__  "bar").readNullable[Bar].map {
            case Some(bar) => Foo(bar.value)
            case None => Foo("")
          }
      }

但是我遇到这样的编译器问题：

[error]  found   : play.api.libs.json.Reads[com.me.Foo]
[error]  required:com.me.Foo

我如何解决这个问题？

Answer 1

import play.api.libs.json._
case class Foo(lorem: String)
implicit val fooReads: Reads[Foo] = Json.reads[Foo]
case class Bar(value: String)
implicit val barReads: Reads[Bar] = Json.reads[Bar]
val reads: Reads[Foo] = (__  "foo").read[Foo].orElse {
  (__  "bar").readNullable[Bar].map {
    case Some(bar) => Foo(bar.value)
    case None => Foo("")
  }
}
// ---
Json.parse("""{"foo":{"lorem":"ipsum"}}""").validate(reads)
// JsSuccess(Foo(ipsum),/foo)
Json.parse("""{"bar":{"value":"ipsum"}}""").validate(reads)
// JsSuccess(Foo(ipsum),/bar)

由于在orElse中实例化Bar没有价值：

val reads: Reads[Foo] = (__  "foo").read[Foo].orElse {
  (__  "bar"  "value").readNullable[String].map {
    case Some(bar) => Foo(bar)
    case None => Foo("")
  }
}