active_record_remote_dbs.rb

class Remote < ActiveRecord::Base
  @abstract_class = true

  def self.db_context(db_name, &block)
    if block_given?
      block.call remote_class(db_name)
    else
      return remote_class(db_name)
    end
  end

  private

  def self.remote_classes
    @remote_classes ||= {}
  end

  # returns proper class from cache or creates new one
  def self.remote_class(db_name)
    remote_classes[db_name] ||= begin
      # creates dynamically descendant Class of self
      remote_class = Class.new(self)
      remote_class.class_eval { establish_connection db_hash(db_name) }
      remote_class
    end
  end

  def self.db_hash(db_name)
    # returns db hash for connection to db_name
  end

end

class RemoteSomething < Remote
  @abstract_class = true
  set_table_name "somethings"

  # actual model definition
  # validations, callbacks etc for Something
end

# usage
# finds all objects in DB db_name
RemoteSomething.db_context(db_name).all
# or with block
RemoteSomething.db_context(db_name) do |klass|
  klass.all
  klass.first
end