Play: Bind a form field to a double?

Question

Perhaps I'm just overlooking something obvious but I can't figure out how to bind a form field to a double in a Play controller.

For instance, assume this is my model:

case class SavingsGoal(
timeframeInMonths: Option[Int],
amount: Double,
name: String
)

(Ignore that I'm using a double for money, I know that's a bad idea, this is just a simplified example)

And I wanted to bind it like so:

object SavingsGoals extends Controller {

    val savingsForm: Form[SavingsGoal] = Form(

        mapping(
            "timeframeInMonths" -> optional(number.verifying(min(0))),
            "amount" -> of[Double],
            "name" -> nonEmptyText
        )(SavingsGoal.apply)(SavingsGoal.unapply)

    )

}

I realized that the number helper only works for ints but I thought using of[] might allow me to bind a double. However, I get a compiler error on this:

Cannot find Formatter type class for Double. Perhaps you will need to import
play.api.data.format.Formats._  

Doing so doesn't help as there's no double formatter defined in the API.

This is all just a long way of asking what's the canonical way of binding a form field to a double in Play?

Thanks!

edit: 4e6 pointed me in the right direction. Here's what I did using his help:

Using the snippets in his link, I added the following to app.controllers.Global.scala:

object Global {

    /**
     * Default formatter for the `Double` type.
     */
    implicit def doubleFormat: Formatter[Double] = new Formatter[Double] {

      override val format = Some("format.real", Nil)

      def bind(key: String, data: Map[String, String]) =
        parsing(_.toDouble, "error.real", Nil)(key, data)

      def unbind(key: String, value: Double) = Map(key -> value.toString)
    }

    /**
     * Helper for formatters binders
     * @param parse Function parsing a String value into a T value, throwing an exception in case of failure
     * @param error Error to set in case of parsing failure
     * @param key Key name of the field to parse
     * @param data Field data
     */
    private def parsing[T](parse: String => T, errMsg: String, errArgs: Seq[Any])(key: String, data: Map[String, String]): Either[Seq[FormError], T] = {
      stringFormat.bind(key, data).right.flatMap { s =>
        util.control.Exception.allCatch[T]
          .either(parse(s))
          .left.map(e => Seq(FormError(key, errMsg, errArgs)))
      }
    }

}

Then, in my form mapping:

mapping(
    "amount" -> of(Global.doubleFormat)
)

Answer 1

You don't need to use the the format in the global if you have the version 2.1 up.

Just import:

import play.api.data.format.Formats._

and use as:

mapping(
    "amount" -> of(doubleFormat)
)

Answer 2

Actually, there is predefined formatter for Double on master branch. So you should either switch to 2.1-SNAPSHOT play version or just copy the implementation.