get all AR::Base descendants

class Class
  def extends?(klass)
    not superclass.nil? and ( superclass == klass or superclass.extends? klass )
  end
  
  def descendants(&block)
    Module.constants.select do |constant_name|
      constant = eval constant_name
      if not constant.nil? and constant.is_a? Class and constant.extends? self
        block_given? ? (constant if block.call(constant)) : constant
      end
    end    
  end
end

class ActiveRecord::Base
  
  def self.models
    descendants { |c| !c.abstract_class? }
  end
end