Adding little stars to the labels of required attributes

form_builder_ext.rb

# Partially stolen from: http://davidsulc.com/blog/2011/05/01/self-marking-required-fields-in-rails-3/

class ActionView::Helpers::FormBuilder
  alias :orig_label :label

  # add a 'required' class to the field label if the field is required
  def label(method, content_or_options = nil, options={}, &block)
    if content_or_options && content_or_options.class == Hash
      options = content_or_options
    else
      content = content_or_options
    end

    validations = object.class.validators_on(method).map(&:class)
    if (validations & [ActiveModel::Validations::PresenceValidator, ActiveModel::Validations::NumericalityValidator]).any?
      options[:class] = "#{options[:class]} required" 
    end

    self.orig_label(method, content, options, &block)
  end
end

labels.css

label.required:after {
  color: red;
  content: " *";
}