CODEWITHSUNDEEP
scalaplayframeworkplayframework-2.0
Soumya Simanta
Soumya Simanta

Reputation: 11741

Implementing writes for a Play 2.1.1

I'm new to Play (and Scala). I'm trying to write a simple Play application that calls some Java code.

I want to convert a scala.collection.mutable.Map[String,Array[String]] to a JSON String. But this clearly doens't work.

Based on this I'm assuming I've to implement Writes. My current code (which is clearly incorrect) looks like the following: 

implicit val myWrites = new Writes[scala.collection.mutable.Map[String,Array[String]]] {

def writes(res: scala.collection.mutable.Map[String,Array[String]]) = {

  val x  = res.foreach { kv => Json.obj(
      kv._1 -> ( kv._2.reduceLeft(_ + "," + _).mkString)

    ) }

    Json.toJson(x)

  }


}

Any pointers that will help me make progress would be appreciated.

Upvotes: 2

Views: 592

Answers (1)

Ionuț G. Stan
Ionuț G. Stan

Reputation: 179119

You don't have to write any Writes implementation. All you need to do is transform the mutable map into an immutable one, simply by calling the toMap method:

scala> import play.api.libs.json._
import play.api.libs.json._

scala> import scala.collection.mutable
import scala.collection.mutable

scala> val im = Map("foo" -> Array("bar", "baz"))
im: scala.collection.immutable.Map[String,Array[String]] = Map(foo -> Array(bar, baz))

scala> Json.stringify(Json.toJson(im))
res8: String = {"foo":["bar","baz"]}

scala> val mm = mutable.Map("foo" -> Array("bar", "baz"))
mm: scala.collection.mutable.Map[String,Array[String]] = Map(foo -> Array(bar, baz))

scala> Json.stringify(Json.toJson(mm))
<console>:20: error: No Json deserializer found for type scala.collection.mutable.Map[String,Array[String]]. Try to implement an implicit Writes or Format for this type.
              Json.stringify(Json.toJson(mm))
                                        ^

scala> Json.stringify(Json.toJson(mm.toMap))
res10: String = {"foo":["bar","baz"]}

Upvotes: 5

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