Q & A at xu_ch see ask a question about the drop-down list. Think of, made a before about using AJAX, dynamic update cascade similar pull-down menu function. To take this opportunity to organize them a bit useless.

It is said that a classic original, I want to look Translate:

http://www.roryhansen.ca/2005/06/21/related-drop-down-lists-with-ruby-and-ajax/

Some complained

However, this code actually creates HTML in the controller component: 

@albums = Album.find_all_by_artist_id(@params["artist_id"])
@html = ""
@html += "No Album"
@albums.each do |@album|
   @html += "#{@album.album_name}"
end
@html += ""


I would think this is considered 'bad practice', because this is the job of
the view.

How could one rewrite this and get a cleaner controller code? 

<select name="yes_or_no" >
  <option value="1">Yes</option>
  <option value="0">No</option>
</select>

<%= observe_field 'yes_or_no',
        :frequency => 1, 
        :update => 'div_to_be_updated',
        :url => {:controller => 'controller', :action=> 'action' }, 
        :with => "'is_delivery_address=' + escape(value)" %>


#in your controller
def action
  if params[:is_delivery_address] == "1"
    render :partial => 'nothing'  
  else 
    render :partial => 'address_partial'  
  end
end



 # _form.rhtml
 <%=  options_from_collection_for_select(Coordinator.find_all, "id",
 "coordinator_name") %>
 #get_projects
 def get_projects
    @results = Project.find_all
    render :partial => 'options'
 end

 # _options.rhtml
 <% for project in @results do -%>
 <%=project.project_number%>
 <% end -%>


controller inside: 
def test
  @provinces = Province.find(:all)
end

def select_with_ajax
  @cities = City.find(params[:province_id])
  render :partial => "select_city"
end 


test.rhtml code: 

<%= javascript_include_tag :defaults %>
<%= select(:province, :id, @provinces.map {|u| [u.name, u.id]},options = {},
  html_options = {"onchange" => remote_function(
    :with=> "'province_id='+value",                                       :update => 'city_select',
    :url => { :action => :select_with_ajax })})
%>


_select_city.rhtml code: 

<%= select(:city, :id, @cities.map{|u| [u.name,u.id]}) %>