Play! framework 2.0: Validate field in forms using other fields

Question

In the play! framework, using scala,say that i have a form such as follows:

import play.api.data._
import play.api.data.Forms._
import play.api.data.validation.Constraints._

case class User(someStringField: String, someIntField: Int)

val userForm = Form(
  mapping(
    "someStringField" -> text,
    "someIntField" -> number verifying(x => SomeMethodThatReceivesAnIntAndReturnsABoolean(x))
  )(User.apply)(User.unapply)

)

where SomeMethodThatReceivesAnIntAndReturnsABoolean is a method that performs some logic on the int to validate it.

However, i would like to be able to consider the value of the someStringField when validating the someIntField, is there a way to achieve this in play framework's forms? I know that i can do something like:

val userForm = Form(
  mapping(
    "someStringField" -> text,
    "someIntField" -> number 
  )(User.apply)(User.unapply)
.verifying(x => SomeFunctionThatReceivesAnUserAndReturnsABoolean(x))

and then i would have the entire user instance available passed to the validation function. The problem with that approach is that the resulting error would be associated with the entire form instead of being associated with the someIntField field.

Is there a way to get both things, validate a field using another field and maintain the error associated to the specific field i wish to validate, instead of the entire form?

Answer 1

I have the same requirements with adding validation to fields depending on the value of other fields. I´m not sure how this is done in idiomatic PLAY 2.2.1 but I came up with the following solution. In this usage I´m degrading the builtin "mapping" into a simple type converter and apply my "advanced inter field" validation in the "validateForm" method. The mapping:

val userForm = Form(
mapping(
  "id" -> optional(longNumber),
  "surename" -> text,
  "forename" -> text,
  "username" -> text,
  "age" -> number
)(User.apply)(User.unapply)
)

private def validateForm(form:Form[User]) = {
  if(form("username").value.get == "tom" || form("age").value.get == "38") {
    form
      .withError("forename", "tom - forename error")
      .withError("surename", "tom - surename error")
  }
  else
    form
}

def update = Action { implicit request =>
  userForm.bindFromRequest.fold({
    formWithErrors => BadRequest(users.edit(validateForm(formWithErrors)))
  }, { user => 
    val theForm = validateForm(userForm.fill(user))
    if(theForm.hasErrors) {
      BadRequest(users.edit(theForm))
    } else {
      Users.update(user)
      Redirect(routes.UsersController.index).flashing("notice" -> s"${user.forename} updated!")
    }
  }) 
} 

Even though it works I´m urgently searching for a more idiomatic version...

EDIT: Use a custom play.api.data.format.Formatter in idiomatic play, more on http://workwithplay.com/blog/2013/07/10/advanced-forms-techniques/ - this lets you programmatically add errors to a form. My Formatter looks like this:

val usernameFormatter = new Formatter[String] {

override def bind(key: String, data: Map[String, String]): Either[Seq[FormError], String] = {
  // "data" lets you access all form data values
  val age = data.get("age").get
  val username = data.get("username").get
  if(age == "66") {
    Left(List(FormError("username", "invalid"), FormError("forename", "invalid")))
  } else {
    Right(username)
  }
}

override def unbind(key: String, value: String): Map[String, String] = {
  Map(key -> value)
}
}
}

Registered in the form mapping like this:

mapping(
[...]
  "username" -> of(usernameFormatter),
[....]