Metaprog: dynamically add methods to a class

date_filterable.rb

module DateFilterable
  private
  def filterable_by(field)
    class_filter = %Q{def filter_by_date(min,max=nil)
  if max.nil?
    where("#{field} > :min_date", { :min_date => min } )
  else
    where("#{field} >= :min_date, #{field} < :max_date", { :min_date => min, :max_date => max } )
  end
end}
    
    field_date_accessor = %Q{def #{field}
  Date.new(Integer read_attribute(:#{field}))
end}

    instance_eval class_filter
    class_eval field_date_accessor

  end
end