Question

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>
...

Answer 1

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