Question

I would like form validation in Play framework to produce a variable error message depending on collateral results of the validation. How can I do this cleanly?

Specific example — Say I have a form defined thus:

  val f = Form(
    "xml" -> text
      .verifying(
        "xml is incorrect",
        xml => validationError(xml) == None
      )
  )

  def validationError(xml: String): Option[String]

What can I do to show the string returned by validationError as the validation error message, instead of the fixed string “xml is incorrect”?

Answer 1

You can create Constraint instance which will handle it. For example:

val xmlConstraint = Constraint[String](Some("xml.constraint"), Nil)( xml =>
  validationError(xml).map(msg => Invalid(ValidationError(msg))).getOrElse(Valid)
)

val f = Form("xml" -> text.verifying(xmlConstraint))

Also, there is another apply method on Constraint object without specifying the name of constraint.