class ScopeValidator

def validate_each(record, attribute, value)
  id_method = :"#{attribute}_id"
  valid_collection = :"valid_#{attribute.to_s.pluralize}"
  if record.send(id_method).present?
    # Don't allow users to assign the IDs of other teams' or users' resources to this attribute.
    unless record.send(valid_collection).exists?(id: record.send(id_method))
      record.errors.add(id_method, :invalid)
    end
  end
end