Using the Carmen gem: https://github.com/jim/carmen.
I did the following some times ago (AJAX).
HTML:
<p>
<label>Country <span>*</span></label>
<%= profile_form.select(:country,Carmen.countries, {:include_blank => 'Select a Country'}, :id => "profile_country") %>
</p>
<p>
<label>State <span>*</span></label>
<%= profile_form.select(:state, "" , {:include_blank => 'Select a Country first'}, :id => "profile_state") %>
</p>
Controller:
def states
begin
render :json => Carmen::states(CGI::unescape(params[:country]))
rescue
render :json => {"content" => "None"}.to_json
end
end
Javascript with jQuery:
$('#profile_country').change(function() {
if ($(this).val() == '')
{
$('#profile_state').empty();
$('#profile_state').append( $('<option>No state provided for your country</option>'));
}
else {
$.ajax({
type: "GET",
url: "/remote/get_states/" + encodeURIComponent($(this).attr('value')),
success: function(data){
if (data.content == 'None')
{
$('#profile_state').empty();
$('#profile_state').append( $('<option>No state provided for your country</option>'));
}
//handle the case where no state related to country selected
else
{
$('#profile_state').empty();
$('#profile_state').append( $('<option>Select your State</option>'));
jQuery.each(data,function(i, v) {
$('#profile_state').append( $('<option value="'+ data[i][1] +'">'+data[i][0] +'</option>'));
});
}
}
});
}
});