Validating Multiple Fields in Rails

gistfile1.rb

  validate :unique_organisation_entry

  def unique_organisation_entry
    matched_entry = Organisation.where(['LOWER(name) = LOWER(?) AND LOWER(company_no) = LOWER(?) AND LOWER(postcode) = LOWER(?)', self.name, self.company_no, self.postcode]).first
    errors.add(:base, 'I know you think you\'re clever, but someone already submitted that one.') if matched_entry && (matched_entry.id != self.id)
  end