constraints.scala

val fieldConstraints = form.mapping.mappings.map(m => m.key -> m.constraints)

mapping.scala

  val tokenListMapping = list(
    mapping(
      "id" -> text,
      "name" -> text,
      "tokenType" -> optional (text),
      "data" -> optional(of[Map[String, String]])
      )(Token.apply)(Token.unapply)
    )

  val groupForm: Form[GroupViewModel] = Form(
    mapping(
      "id" -> optional(of[ObjectId]),
      "name" -> nonEmptyText,
      "grantType" -> nonEmptyText,
      "canChangeGrantType" -> boolean,
      "users" -> tokenListMapping.withPrefix ("users"),
      "dataSets" -> tokenListMapping.withPrefix ("dataSets"),
      "errors" -> of[Map[String, String]]
    )(GroupViewModel.apply)(GroupViewModel.unapply)
  )