gistfile1.txt

class BarcodeForm
  include Virtus.model
  include ActiveModel::Validations

  attribute :barcode, String
  attribute :job_number, Integer
  attribute :sample_number, Integer
  
  validates :other, :presence=>true

  validate do
    if barcode.present? && sample_details_present?
      errors.add :base, "Can only enter data into barcode OR job/sample fields, not both"
    elsif barcode.blank? && job_number.blank? && sample_number.blank?
      errors.add :base, "You didn't enter anything!"
    end

  end

  def sample_details_present?
    job_number.present? || sample_number.present?
  end

end

... controller ..

form = BarcodeForm.new params[:barcode]
if form.valid?

end

...