In the view

navigations_controller.rb

class NavigationsController < ApplicationController
  def cities
    @cities = City.find(:all,  :order => 'name')
    @cities.map!{|c|
      {
        :id => c.id,
        :name => c.name
      }
    }
    respond_to do |format|
      format.json { render :json => @cities }
    end
  end
end

search.html.erb

    <%= sell_search_form.input :city_id,
      :label => t("Град", :scope => [:admin, :buy_search]),
      :as => :select,
      :collection => []
  %>

 <% content_for :head do %>
      <script type="text/javascript">
        
        function fill_from_storage(target_select, storage_name, data_url, value) {
          // localStorage.removeItem("cities_storage" + "_options")
          // localStorage.removeItem("cities_storage")
 
          var json_stored_data = localStorage.getItem(storage_name);
          if (json_stored_data == null) {
            $.getJSON(data_url, function(data) {
              var select_options = '';
              // use http://code.google.com/p/jquery-json/
              var encoded = $.toJSON(data);
              localStorage.setItem(storage_name, encoded); // store the raw data

              // Store parsed options tags
              $(data).each(function(index, object) {
                select_options += '<option value="' + object.id + '">' + object.name + '</option>';
              });

              localStorage.setItem(storage_name + "_options", select_options); // store the raw data
              $(target_select).html(localStorage.getItem(storage_name + "_options"));
              $(target_select).val(value);
            });
          } else {
            // we don't need the raw data'
            // data = localStorage.getItem(storage_name);
            // items = jQuery.parseJSON(data);

            $(target_select).html(localStorage.getItem(storage_name + "_options"));
            $(target_select).val(value);
          }
        }

        $(document).ready(function(){
          fill_from_storage("#sell_search_city_id", "cities_storage", "<%= cities_navigations_path %>", <%= sell_search_form.object.city_id %>);
        });
      </script>
    <% end%>