使用akka-http时的问题，circe

Question

Let's say I have this hierarchy:

sealed trait Animal {
  def eat = println("eating!")
}
final case class Dog(name :String) extends Animal {override def eat= println("dog eating")}
final case class Cat(name: String) extends Animal {override def eat= println("cat eating")}

As you see I'm using akka http and circe, then I have the following:

import io.circe.syntax._
import io.circe.Json
...
pathPrefix("path" / "something") { 
post {
   entityAs[Map[String,Json]] { data => 

      // depending on the key of the map I will create an object Dog or Animal
      val transformed = data.map { d => 
         d._1 match {
            case "dog" => d._2.as[Dog]
            case "cat" => d._2.as[Cat]
         }
      }

      // then I will do something like
      transformed.foreach(_.eat)

      complete(Status.OK)
   }
}

But for some reason I can't use the method eat . And I see that the type of transformed is immutable.Iterable[Result[_ >: Dog with Cat <: Animal]] I guess that's the problem that prevent me to call eat method.

Is there anyway to fix that to be able to call the eat event?

Answer 1

As you noticed, the value you are getting is:

Iterable[Result[_ >: Dog with Cat <: Animal with Product]]

while:

final type Result[A] = Either[DecodingFailure, A]

In order to access the eat method, you have to do:

transformed.foreach(_.map(_.eat))

Answer 2

From you point of view, every time when map key is dog, its value is Dog class, but from compiler doesn't know about that.

That is why transformed is Iterable[Result[X]] , and when traversing iterable you are trying to call eat method on Result type.

You have to extract value from Result object, only if it was deserialized correctly