Custom validation of Play 2.0 form (scala) - validation

Question

I'm writing a little hobby app. Now, in my application I want people to have a userId (just like mine is niklassaers here on stack overflow), and if it is already taken, I want the user to get an error so he can select another.
Here follows my Signup object, it gives me an error at the line "mapping(": "missing arguments for method mapping in object Forms; follow this method with `_' if you want to treat it as a partially applied function"
object Signup extends Controller {
val userForm: Form[UserProfile] = Form(
mapping(
"userId" -> nonEmptyText,
"passwordHash" -> nonEmptyText,
"email" -> email
) verifying (
"ThisIsATest", { case(userId, passwordHash, email) => true }
// "UserID already taken", { DBService.exists(UserProfile.getClass().getName(), userId) }
)(UserProfile.apply)(UserProfile.unapply))
def index = Action {
Ok(views.html.signup(userForm))
}
def register = Action { implicit request =>
userForm.bindFromRequest.fold(
errors => BadRequest(views.html.signup(errors)),
user => Redirect(routes.Profile.index))
}
}
As you can see, I've replaced my lookup service with a test verification that simply returns true, to make the example less complex. For completeness, this is my UserDetail case class:
case class UserProfile(
userId : String,
email: String,
passwordHash: String)
I'm a Scala newbie and Play newbie, so I'm sorry if this is a very trivial question. But:
What am I doing wrong since I get this error?
Is this the right way of adding my own validation?
Follow-up question: I redirect if it goes well, but how should I redirect to a page referencing the just verified form?
Cheers
Nik

Answer 1

Finally got around this: verifying isn't something that comes after mapping, it is something that comes at the constraint. So it should be
"userId" -> nonEmptyText.verifying( "UserID already taken", userId => DBService.exists(UserProfile.getClass().getName().replace("$", ""), userId) == false ),
I hope this helps others that have the same problem :-)

Answer 2

A little late, but anyway..
You can do validation on the whole "form-backing object" instead of just a single field as you ended up with. This is similar to the first code you posted in your problem description. The problem is that your verifying block needs to be after the apply/unapply statements.
case class UserRegistration(username: String, password1: String, password2: String)
val loginForm = Form(
mapping(
"username" -> email,
"password1" -> text,
"password2" -> text
)
(UserRegistration.apply)(UserRegistration.unapply)
verifying ("Passwords must match", f => f.password1 == f.password2)
)

Answer 3

Even later, but anyway... :)
Using verifying on the entire "form backing object" doesn´t let you add errors to individual fields in the form. If you want to do that see Play! framework 2.0: Validate field in forms using other fields