Play Framework 2.1 / form mapping with complex objects

Question

Play Framework documentation for Scala shows a sample mapping a form to a case class implicitly:

case class User(name: String, age: Int)

val userForm = Form(
  mapping(
    "name" -> text,
    "age" -> number
  )(User.apply)(User.unapply)
)

We notice that only primitive values are used in this unique sample.

How about if we make this alteration:

case class Car(brandName: String)

case class User(name: String, car: Car)

Moreover, let's assume that the form returns the User's name (String) and a carId(String)

val userForm = Form(
  mapping(
    "name" -> text,
    "car" -> carRepository.findById(nonEmptyText)  // concept I wish
  )(User.apply)(User.unapply)
)

Is there any way to instantiate a car at this wished line with some carId provided for example by the form and ensuring also that the carId is not an empty String?

Answer 1

For first part of your question, documentation also shows Nested values:

case class Car(brandName: String)
case class User(name: String, car: Car)

val userForm = Form(
  mapping(
    "name" -> text,
    "car" -> mapping(
        "brandName" -> text
    )(Car.apply)(Car.unapply)
  )(User.apply, User.unapply)
)

Answer 2

You could supply a Formatter and use the of[Car] method.

implicit val carFormat = new Formatter[Car] {
  def bind(key: String, data: Map[String, String]):Either[Seq[FormError], Car] = 
    data.get(key)
      // make sure the method returns an option of Car
      .flatMap(carRepository.findByBrandName _)
      .toRight(Seq(FormError(key, "error.carNotFound", Nil)))

  def unbind(key: String, value: Car) = Map(key -> value.brandName)
}

This answer provides another Formatter: Play 2 - Scala - Forms Validators and radio buttons

You can then use it like this:

val userForm = Form(
  mapping(
    "name" -> text,
    "car" -> of[Car]
  )(User.apply)(User.unapply)
)