Play 2.3 scala forms - how to customise constraint messages - forms

Question

I've created form in play framework with constraints:
val voucherForm = Form(
mapping(
"voucherName" -> nonEmptyText,
"voucherCode" -> optional(text(minLength = 6).verifying(pattern("""[a-zA-Z0-9]+""".r, error = "...")))
)(VoucherForm.apply)(VoucherForm.unapply)
)
when I display this form on a web page I have constraint messages (like Required, Minimum length: 6, constraint.pattern) shown near input boxes.
I want to customise this constraint messages per input field (i.e. two nonEmptyText constraints in same form will have different constraint message). How could I do it?

Answer 1

Instead of using nonEmptyText, could you not use text, and put your custom message in the verifying, along the lines of:
val voucherForm = Form(
mapping(
"voucherName" -> text.verifying(
"Please specify a voucher name", f => f.trim!=""),
...

Answer 2

These messages are taken from, well, messages. You can create your custom messages file and put there your custom text. Navigate through sources to check what is the valid string to put there.
For example nonEmptyText is declared as follows:
val nonEmptyText: Mapping[String] = text verifying Constraints.nonEmpty
and from there, Constraints.nonEmpty looks like this:
def nonEmpty: Constraint[String] = Constraint[String]("constraint.required") { o =>
if (o == null) Invalid(ValidationError("error.required")) else if (o.trim.isEmpty) Invalid(ValidationError("error.required")) else Valid
}
so the error string is "error.required"
now you can create a file messages in conf directory and put there a line
error.required=This field is required
ValidationError has apply method declared like this:
def apply(message: String, args: Any*)
which means you can also pass arguments there, in messages you can access them using {arg_num} syntax
If you for example created error like this
val format = ???
ValidationError("error.time", someFormat)
That will be returned with a bounded form, then play will use MessagesApi to find a message named "error.time" and format it accordingly, you could for example create a message like this:
error.time=Expected time format is {0}
My idea to have a custom message for each field is a custom method like this:
def nonEmptyTextWithError(error: String): Mapping[String] = {
Forms.text verifying Constraint[String]("constraint.required") { o =>
if (o == null) Invalid(ValidationError(error)) else if (o.trim.isEmpty) Invalid(ValidationError(error)) else Valid
}
}
probably not an ideal solution if you want to use many kids of constraints.