affiliate_subdomain.rb

#routes
constraints(AffiliateSubdomain) do
  match '/', to: 'affiliates/properties#index', via: :all
end


#libs/affiliate_subdomain.rb
class AffiliateSubdomain
  def self.matches? request
    matching_site?(request)
  end

  def self.matching_site?(request)
    self.get_affiliate(request).any?
  end

  def self.get_subdomain(request)
    if request.subdomain.include?('www')
      request.host[4..-1] # remove 'www.'
    else
      request.host
    end
  end

  def self.get_affiliate(request)
    req = self.get_subdomain(request)
    Affiliate.where(:slug => req)
  end
end