gistfile1.rb

class Search < ActiveRecord::Base
  has_many :search_results
  has_many :cars, :through => :search_results, :source => :results, :source_type => "Car"
  has_many :dealers, :through => :search_results, :source => :results, :source_type => "Dealer"

  # search.results gives you the list of linked records
  has_many :results, :class_name => "SearchResult"
end

class SearchResult < ActiveRecord::Base
  belongs_to :search
  # can be polymorphically linked to anything that is a resultant
  belongs_to :results, :polymorphic => true
end

class Car < ActiveRecord::Base
  # cars can be results
  has_many :search_results, :as => :results
  # -> car.searches gets you the list of searches
  has_many :searches, :through => :search_results
end

class Dealer < ActiveRecord::Base
  # dealers can be results
  has_many :search_results, :as => :results
  # -> dealer.searches gets you the list of searches
  has_many :searches, :through => :search_results
end