HOW DO I populate options from previous option click

I have a form with three drop down option lists. Currently each of these
contain full listings as instantiated in the controller on entering
the edit action. What I would like to do is filter the second list based
on what the user selected on the first and the third filtered to reflect
the second.
For example I have major_role, role and person_in_role = role is a
subset of major_role and person_in_role is one qualified to act in role
Kind Regards,


I figure that even if my answer is semi useless, it is still better
than no answer. I hope you agree. And with that out the way, here
is the help I can offer.

It seems to me that there are three ways to achieve the effect you want.

  1. A round trip to the server. That would be easy, so I doubt that
    is what you want.

  2. Some hideously complex javascript stuff that I still have
    nightmares about since I last had to do something like this. (I
    believe debugging javascript has improved since then, firefox is your

  3. Some wonderful ajax stuff. Sadly, this is where I become
    completely useless to you since I have been focusing on other aspects
    of rails thus far. From what I have read and seen, ajax is going to
    be nicer to you than doing javascript and nicer to the customers than


Change this according to your own needs:

  1. View:

<%= select_tag(‘search[category]’, SELECT OPTIONS HERE) %>

<%= observe_field ‘search[category]’, :url => {:action =>
‘search_sub_category_xhr’}, :update => ‘sub_category_wrapper’, :with
=> “‘category_id=’ + escape(value)”, :complete => visual_effect
(:highlight, ‘sub_category_wrapper’) %>

  1. Now create a new action “search_sub_category_xhr”

    def search_sub_category_xhr
    if params[:category_id] =~ /^[0-9]+$/
    @sub_categories = Category.find(params[:category_id]).children
    render :action => ‘search_sub_category_xhr’, :layout => false

    if @sub_categories.empty?
    render :nothing => true

  2. View for “search_sub_category_xhr”

<%= select_tag ‘search[sub_category]’,
options_from_collection_for_select(@sub_categories, ‘id’, ‘name’) %>

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