ruby on rails f.select options with custom attributes

I have a form select statement, like this:

= f.select :country_id, @countries.map{ |c| [c.name, c.id] }

Which results in this code:

...
<option value="1">Andorra</option>
<option value="2">Argentina</option>
...

But I want to add a custom HTML attribute to my options, like this:

...
<option value="1" currency_code="XXX">Andorra</option>
<option value="2" currency_code="YYY">Argentina</option>
...

Rails CAN add custom attributes to select options, using the existing options_for_select helper. You almost had it right in the code in your question. Using html5 data-attributes:

<%= f.select :country_id, options_for_select(
    @countries.map{ |c| [c.name, c.id, {'data-currency_code'=>c.currency_code}] }) %>

Adding an initial selection:

<%= f.select :country_id, options_for_select(
    @countries.map{ |c| [c.name, c.id, {'data-currency_code'=>c.currency_code}] }, 
    selected_key = f.object.country_id) %>

If you need grouped options, you can use the grouped_options_for_select helper, like this (if @continents is an array of continent objects, each having a countries method):

<%= f.select :country_id, grouped_options_for_select(
    @continents.map{ |group| [group.name, group.countries.    map{ |c| [c.name, c.id, {'data-currency_code'=>c.currency_code}] } ] }, 
    selected_key = f.object.country_id) %>

Credit should go to paul @ pogodan who posted about finding this not in the docs, but by reading the rails source. https://web.archive.org/web/20130128223827/http://www.pogodan.com/blog/2011/02/24/custom-html-attributes-in-options-for-select

You could do this as follows:

= f.select :country_id, @countries.map{ |c| [c.name, c.id, { 'data-currency-code' => c.currency_code} ] }

This is not possible directly with Rails, and you'll have to create your own helper to create the custom attributes. That said, there are probably two different ways to accomplish what you want:

(1) Using a custom attribute name in HTML5. In HTML5 you are allowed to have custom attribute names, but they have to be pre-pended with 'data-'. These custom attributes will not get submitted with your form, but they can be used to access your elements in Javascript. If you want to accomplish this, I would recommend creating a helper that generates options like this:

<option value="1" data-currecy-code="XXX">Andorra</option>

(2) Using values with custom splitting to submit additional data. If you actually want to submit the currency-code, I would recommend creating your select box like this:

= f.select :country_id, @countries.map{ |c| [c.name, "#{c.id}:#{c.currency_code}"] }

This should generate HTML that looks like this:

<option value="1:XXX">Andorra</option>
<option value="2:YYY">Argentina</option>

Which you can then parse in your controller:

@id, @currency_code = params[:country_id].split(':')

The extra attributes hash is only supported in Rails 3.

If you're on Rails 2.x, and want to override options_for_select

I basically just copied the Rails 3 code. You need to override these 3 methods:

def options_for_select(container, selected = nil)
    return container if String === container
    container = container.to_a if Hash === container
    selected, disabled = extract_selected_and_disabled(selected)

    options_for_select = container.inject([]) do |options, element|
      html_attributes = option_html_attributes(element)
      text, value = option_text_and_value(element)
      selected_attribute = ' selected="selected"' if option_value_selected?(value, selected)
      disabled_attribute = ' disabled="disabled"' if disabled && option_value_selected?(value, disabled)
      options << %(<option value="#{html_escape(value.to_s)}"#{selected_attribute}#{disabled_attribute}#{html_attributes}>#{html_escape(text.to_s)}</option>)
    end

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

def option_text_and_value(option)
  # Options are [text, value] pairs or strings used for both.
  case
  when Array === option
    option = option.reject { |e| Hash === e }
    [option.first, option.last]
  when !option.is_a?(String) && option.respond_to?(:first) && option.respond_to?(:last)
    [option.first, option.last]
  else
    [option, option]
  end
end
    
def option_html_attributes(element)
  return "" unless Array === element
  html_attributes = []
  element.select { |e| Hash === e }.reduce({}, :merge).each do |k, v|
    html_attributes << " #{k}=\"#{ERB::Util.html_escape(v.to_s)}\""
  end
  html_attributes.join
end

Kinda messy but it's an option. I place this code in a helper module called RailsOverrides which I then include in ApplicationHelper. You can also do a plugin/gem if you prefer.

One gotcha is that to take advantage of these methods you must always invoke options_for_select directly. Shortcuts like

select("post", "person_id", Person.all.collect {|p| [ p.name, p.id, {"data-stuff"=>"html5"} ] })

will yield the old results. Instead it should be:

select("post", "person_id", options_for_select(Person.all.collect {|p| [ p.name, p.id, {"data-stuff"=>"html5"} ] }))

Again not a great solution, but it might be worth it to get to the ever so useful data-attribute.

I ran into this issue as well and created the "enhanced_select" Ruby Gem to solve this problem. You can find it here:

https://github.com/bkuhlmann/enhanced_select