select option to a select_tag after submitting form

rubyonrails-talk
1

How can I keep the selected option in the select_tag after submitting a form to the same page?

Form <%= select_tag :city_id, options_from_collection_for_select(City.find(:all), :id, :name) %>

After submit the page renders and then I want the selected city to be displayed in the select_tag, how can I do this?

<select name="advertisement_country_id" id="advertisement_country_id"> <option value="">All cities</option> <option value="1">Stockholm</option> <option value="2" selected="selected">Göteborg</option> <---- for example if this was the choice ...and so on </select>

THANKS!