gistfile1.rb

class ExternalDbModel < ActiveRecord::Base
  self.abstract_class = true
  
  establish_connection "external_#{RAILS_ENV}"

# only need this if you want the other db to be readonly
#private
#  def after_initialize
#    readonly!
#  end
end

class InternalModel < ActiveRecord::Base
  self.abstract_class = true
end


# this class points to the external DB
class SomeOutsideModel < ExternalDbModel
  has_many :foos
end

# this class points to the internal DB
class SomeInsideModel < InternalModel
  has_many :bars
end