Store a hash in form hidden fields

form_hidden_fields_helper.rb

module FormHiddenFieldsHelper

  # Originally based on http://marklunds.com/articles/one/314
  def spread_param_hash(hash, key_prefix = '')
    format_key = key_prefix.blank? ? lambda { |k| k.to_s } :
                                     lambda { |k| "#{key_prefix}[#{k}]" }
    flat_hash = {}
    hash.each do |k, v|
      k = format_key.call(k)
      if v.is_a?(Hash)
        flat_hash.merge!(spread_param_hash(v, k))
      else
        flat_hash[k] = v
      end
    end
    flat_hash
  end

  def hidden_field_tags_from_hash(hash, options = {})
    hidden_field_tags = []
    spread_param_hash(hash).each do |name, value|
      if value.is_a?(Array)
        name << '[]'
        value.each do |v|
          hidden_field_tags << hidden_field_tag(name, v, options)
        end
      else
        hidden_field_tags << hidden_field_tag(name, value, options)
      end
    end

    hidden_field_tags.join("\n").html_safe
  end
end