Question

I understand how to add simple form validations in Play 2 such as nonEmptyText, but how would I implement more complex validations such as “at least one of the fields must be defined”? Presently I throw an exception in my model object if it gets initialized with all Nones, but this generates a nasty error message. I would prefer to get a friendly error message on the form page.

Answer 1

You can nest the mappings/tuples in your form definition and add verifying rules on mapping, sub-mapping, tuple and sub-tuple.
Then in your templates you can retrieve the errors using form.errors("fieldname") for a specific field or a group a fields.

For example :

val signinForm: Form[Account] = Form(
    mapping(
        "name" -> text(minLength=6, maxLength=50),
        "email" -> email,
        "password" -> tuple(
            "main" -> text(minLength=8, maxLength=16),
            "confirm" -> text
        ).verifying(
            // Add an additional constraint: both passwords must match
            "Passwords don't match", password => password._1 == password._2
        )
    )(Account.apply)(Account.unapply)
)

If you have two different passwords, you can retrieve the error in your template using form.errors("password")

In this example, you will have to write your own Account.apply and Account.unapply to handle (String, String, (String, String))