How to add a css class to start_form_tag in Ruby on Rails

Posted on 07 April 2006

To add a class to a form in Ruby on Rails using start_form_tag isn't immediately obvious. I achieved it like this:

<%= start_form_tag( {}, {:class => 'classnamehere'}) %>

The empty curly brackets are where you might enter the controller or action.

The key part to the start_form_tag helper though, are the brackets ( ) which aren't necessary for many other helpers, this is an odd inconsistency in Rails that I have found.

Incidently start_form_tag is an alias for form_tag so it does exactly the same thing.

The following is taken from the Rails API that helped me figure this out.

def form_tag(url_for_options = {}, options = {}, *parameters_for_url, &proc)
  html_options = { "method" => "post" }.merge(options.stringify_keys)
  html_options["enctype"] = "multipart/form-data" if      html_options.delete("multipart")
  html_options["action"] = url_for(url_for_options, *parameters_for_url)
  tag :form, html_options, true
end

Update 24/05/07

Note that start_form_tag is now deprecated and that in Rails 2.0 you will need to switch to the following:

<% form_tag({:action => "foo"},{:class => "bar"}) do %>
  insert code
<% end %>

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