distributor.rb

class Distributor
  belongs_to :environment
  # ...
  validate name_uniq_in_org
  
  def name_uniq_in_org
    others = self.where(:name => self.name).join(:environment).
      where("enivronment.organization_id" => self.environment.organization_id)
    others.where("id != ?", self.id) if self.id
    errors.add(:base, "name already taken") if others.any?
  end
  
end