Route domains root to resources show

domain.rb

class Domain < ActiveRecord::Base
  validates :name, :presence => true, :uniqueness => true
  validates :routable, :presence => true

  belongs_to :routable, :polymorphic => true
end

post.rb

class Post < ActiveRecord::Base
  extend RouteByDomain

  has_one :domain, :as => :routable
end

route_by_domain.rb

module RouteByDomain
  def matches?(request)
    return unless request.get?
    domain = Domain.find_by_routable_type_and_name(self.to_s, request.host)
    return unless domain
    request.params[:id] = domain.routable_id 
  end
end

routes.rb

Rails3Routing::Application.routes.draw do |map|
  constraints(Post) do
    root :to => "events#show"
  end
  root :to => "welcome#index"

  resources :posts
end