Rails: add field to all forms

Question

Is it possible to add hidden field to all form tags? I'm trying to do it in following way:

module ActionView::Helpers::FormTagHelper

  def form_tag(url_for_options = {}, options = {}, &block)
    html_options = html_options_for_form(url_for_options, options)
    if block_given?
      f = form_tag_in_block(html_options, &block)
    else
      f = form_tag_html(html_options)
    end
    hidden_f = ActiveSupport::SafeBuffer.new "<input name='n' type='hidden' value='v' /><\/form>"
    f.gsub!(/<\/form>/, hidden_f)
    f
  end

end

But server shows the error:

ActionView::Template::Error (Could not concatenate to the buffer because it is not html safe.):

How should i do it?

Answer 1

It might be simpler to redefine the extra_tags_for_form method, which is used to add the _method, utf8, and authenticity_token hidden fields. Something like this could work:

module ActionView::Helpers::FormTagHelper
  alias_method :orig_extra_tags_for_form, :extra_tags_for_form

  def extra_tags_for_form(html_options)
    orig_tags = orig_extra_tags_for_form(html_options)
    orig_tags << "<input name='n' type='hidden' value='v' /><\/form>".html_safe
  end
end

Since this advice involves redefining a private method, you will need to be sure to test it carefully any time you upgrade Rails.

Answer 2

Try with

module ActionView::Helpers::FormTagHelper
  def form_tag(url_for_options = {}, options = {}, &block)
    html_options = html_options_for_form(url_for_options, options)
    if block_given?
      f = form_tag_in_block(html_options, &block)
    else
      f = form_tag_html(html_options)
    end
    hidden_f = ActiveSupport::SafeBuffer.new "<input name='n' type='hidden' value='v' /><\/form>"
    f.gsub!(/<\/form>/, hidden_f)
    f.html_safe
  end
end

gsub! taints your string with HTML unsafeness.