Question

我有两个案例类：

首先：

object Person {
  implicit val jsonFormat = Json.format[Person]
}

case class Person(name: String, coWorkers: List[CoWorker])

人可能有0或某些CoWorkers

第二

object CoWorker {
  implicit val jsonFormat: Format[CoWorker] = Json.format[CoWorker]
}

case class CoWorker(position: String, person: Person)

我做了测试：

import org.specs2.mutable.Specification
import play.api.libs.json.{JsError, JsArray, Json}

class NestedSpec extends Specification {

  "Nested" should {

    "jsonReads" in {

      val personJson = Json.obj(
        "name" -> "alex",
        "coWorkers" -> Json.arr(
          Json.obj(
            "person" -> Json.obj(
              "name" -> "jack",
              "coWorkers" -> List.empty[String]
            ),
            "position": "developer" 
          )
        )
      )

      val res = personJson.validate[Person].asEither

      res.left.map(err => println(Json.prettyPrint(JsError.toJson(err))))

      res.isRight must beTrue

    }

  }

}

但该测试失败并出现错误：

> testOnly  nested.NestedSpec
[info] NestedSpec
[info] 
[info] Nested should
[error]   ! jsonReads
[error]    java.lang.NullPointerException: null (JsConstraints.scala:32)
[error] play.api.libs.json.PathReads$$anonfun$at$1$$anonfun$apply$2.apply(JsConstraints.scala:32)
[error] play.api.libs.json.PathReads$$anonfun$at$1$$anonfun$apply$2.apply(JsConstraints.scala:32)
[error] play.api.libs.json.JsResult$class.flatMap(JsResult.scala:99)
[error] play.api.libs.json.JsSuccess.flatMap(JsResult.scala:9)
[error] play.api.libs.json.PathReads$$anonfun$at$1.apply(JsConstraints.scala:32)
[error] play.api.libs.json.PathReads$$anonfun$at$1.apply(JsConstraints.scala:32)
[error] play.api.libs.json.Reads$$anon$8.reads(Reads.scala:126)
[error] play.api.libs.json.OFormat$$anon$2.reads(Format.scala:46)
[error] play.api.libs.json.Reads$$anon$3$$anon$4.reads(Reads.scala:104)
[error] play.api.libs.json.OFormat$$anon$2.reads(Format.scala:46)
[error] play.api.libs.json.OFormat$$anon$5$$anonfun$inmap$1.apply(Format.scala:31)
[error] play.api.libs.json.OFormat$$anon$5$$anonfun$inmap$1.apply(Format.scala:31)
[error] play.api.libs.json.OFormat$$anon$1.reads(Format.scala:39)
[error] play.api.libs.json.Json$.fromJson(Json.scala:125)
[error] play.api.libs.json.LowPriorityDefaultReads$$anon$2$$anonfun$reads$1.apply(Reads.scala:168)
[error] play.api.libs.json.LowPriorityDefaultReads$$anon$2$$anonfun$reads$1.apply(Reads.scala:167)
[error] play.api.libs.json.LowPriorityDefaultReads$$anon$2.reads(Reads.scala:167)
[error] play.api.libs.json.DefaultFormat$$anon$4.reads(Format.scala:82)
[error] play.api.libs.json.PathReads$$anonfun$at$1$$anonfun$apply$2.apply(JsConstraints.scala:32)
[error] play.api.libs.json.PathReads$$anonfun$at$1$$anonfun$apply$2.apply(JsConstraints.scala:32)
[error] play.api.libs.json.JsResult$class.flatMap(JsResult.scala:99)
[error] play.api.libs.json.JsSuccess.flatMap(JsResult.scala:9)
[error] play.api.libs.json.PathReads$$anonfun$at$1.apply(JsConstraints.scala:32)
[error] play.api.libs.json.PathReads$$anonfun$at$1.apply(JsConstraints.scala:32)
[error] play.api.libs.json.Reads$$anon$8.reads(Reads.scala:126)
[error] play.api.libs.json.OFormat$$anon$2.reads(Format.scala:46)
[error] play.api.libs.json.Reads$$anon$3$$anon$4.reads(Reads.scala:104)
[error] play.api.libs.json.OFormat$$anon$2.reads(Format.scala:46)
[error] play.api.libs.json.OFormat$$anon$5$$anonfun$inmap$1.apply(Format.scala:31)
[error] play.api.libs.json.OFormat$$anon$5$$anonfun$inmap$1.apply(Format.scala:31)
[error] play.api.libs.json.OFormat$$anon$1.reads(Format.scala:39)
[error] play.api.libs.json.JsValue$class.validate(JsValue.scala:18)
[error] play.api.libs.json.JsObject.validate(JsValue.scala:76)
[error] nested.NestedSpec$$anonfun$1$$anonfun$apply$2.apply(NestedSpec.scala:24)
[error] nested.NestedSpec$$anonfun$1$$anonfun$apply$2.apply(NestedSpec.scala:10)
[info] 
[info] 
[info] 
[info] Total for specification NestedSpec
[info] Finished in 269 ms
[info] 1 example, 0 failure, 1 error
[info] 
[error] Error: Total 1, Failed 0, Errors 1, Passed 0
[error] Error during tests:
[error]         nested.NestedSpec
[error] (test:testOnly) sbt.TestsFailedException: Tests unsuccessful
[error] Total time: 1 s, completed May 18, 2016 12:25:16 PM

我认为这是一种课程依赖错误。 CoWorker使用Person的jsonReads，Person使用CoWorker jsonReads。有可能解决这个问题并让测试运行吗？

Answer 1

我需要使用lazyReads，可以在docs中找到：

递归类型我们的示例模型没有的一种特殊情况演示如何处理递归类型的读取和写入。 JsPath提供了call-by-name的lazyRead和lazyWrite方法处理这个的参数：
case class User(name: String, friends: Seq[User])

implicit lazy val userReads: Reads[User] = (
  (__ \ "name").read[String] and
  (__ \ "friends").lazyRead(Reads.seq[User](userReads))
)(User)

implicit lazy val userWrites: Writes[User] = (
  (__ \ "name").write[String] and
  (__ \ "friends").lazyWrite(Writes.seq[User](userWrites))
)(unlift(User.unapply))

https://www.playframework.com/documentation/2.5.x/ScalaJsonCombinators#recursive-types

玩json，递归读取，npe

1 个答案: