class Hash

def as_json(options = nil) #:nodoc:
  # create a subset of the hash by applying :only or :except
  subset = if options
    if attrs = options[:only]
      slice(*Array(attrs))
    elsif attrs = options[:except]
      except(*Array(attrs))
    else
      self
    end
  else
    self
  end
  Hash[subset.map { |k, v| [k.to_s, options ? v.as_json(options.dup) : v.as_json] }]
end