Rails 3, prototype and multi-select dependencies base on BBTangCMS

_categories.html.erb

<%= collection_select('question', "category_list", categories, :id, :name,
                     {:prompt   => "Select a category",  :selected => (@question_categories.map(&:id) if @question_categories.present?)}) %>

_form.html.erb

<%= simple_form_for(@question, :html => { :class => "form-inline" }) do |f| %>
  <%= f.error_notification %>

  <div class="form-inputs">
    <%= f.input :title %>
    <!--%= f.input :content %-->
    <%= f.input :body, :as => :kindeditor %>
    <!--%= f.input :focus_by %-->
    <%= f.input :score, :as =>:integer %>
    <!--%= f.input :created_by %-->
    <!--%= f.input :views_count %-->
    <!--%= f.input :delta %-->
    <!--%= f.input :last_answer_time %-->
    <!--%= f.input :best_answer_id %-->

    <span class="label label-info">tags</span>
    <%= f.input :identity_list, :collection => @identities,  :selected => (@question_identities.map(&:id) if @question_identities.present?),
         :input_html => { :rows =>"5", :cols =>"20" ,
             :onchange => "#{remote_function(:url  => {:action => 'update_timelines'},:with => "'identity_id='+value")}"

            }
      %>
    <%= f.input :timeline_list do %>
      <div id="timeline_list">
        <%= render :partial => 'timelines', :object => @timelines  %>
      </div>
    <% end %>
    <%= f.input :category_list do %>
    <div id="category_list">
      <%= render :partial => 'categories', :object => @categories  %>
    </div>
    <% end %>

    <%= f.input :tag_list,:hint => "请输入标签名，并以英文逗号(',')隔开...", :input_html => { :rows =>"5", :cols =>"20" } %>

    <% if @question.new_record? %>
      <%= f.input :created_by, :as => :hidden, :input_html => { :value => (current_user.id if current_user.present?) } %>
      <%= f.input :created_at, :as => :hidden, :input_html => { :value => Time.now } %>
    <% else %>
      <%= f.input :updated_at, :as => :hidden, :input_html => { :value => Time.now} %>
    <% end %>
    <!--%= f.input :answers_count %-->
    <!--%= f.input :experts_count %-->
    <!--%= f.input :designated_answerer %-->
    <!--%= f.input :auto_tags %-->
    <!--%= f.input :knowledge_id %-->
    <%= f.input :is_anonymous %>
    <%= f.input :soft_deleted, :as => :boolean, :input_html => {:checked =>  @question.deleted_at? ? "checked" : ""} %>
    <!--%= f.input :deleted %-->
  </div>

  <div class="form-actions">
    <%= f.button :submit, :class => 'btn-primary', :disable_with => 'loading...' %>
    <%= link_to t('.cancel', :default => t("helpers.links.cancel")),
                questions_path, :class => 'btn' %>
  </div>
<% end %>

_timelines.html.erb

<%= collection_select("question", "timeline_list", timelines, :id, :name,
                     {:prompt   => "Select an timeline",  :selected => (@question_timelines.map(&:id) if @question_timelines.present?)},
                     {:onchange => "#{remote_function(:url  => {:action => "update_categories"},
                                                      :with => "'timeline_id='+value")}"}) %>
<!--%= grouped_collection_select("question", "timeline_list", timelines, :id, :name,
                     {:prompt   => "Select an timeline"},
                     {:onchange => "#{remote_function(:url  => {:action => "update_categories"},
                                                      :with => "'timeline_id='+value")}"})%-->

application.js

//= require jquery
//= require jquery_ujs
//= require jquery-ui
//= require prototype
// require prototype_ujs /* in my case it conflict with jquery_ujs
//= require effects
//= require dragdrop
// require controls
//= require twitter/bootstrap
//= require kindeditor
//= require_tree .

Gemfile

gem "prototype-rails", "~> 3.2.1"

questions_controller.rb

class QuestionsController < ApplicationController
  load_and_authorize_resource
  Model_class = Question.new.class

  # GET /questions
  # GET /questions.json
  def index
    @questions = Question.paginate(:page => params[:page]).order('score DESC')


    breadcrumbs.add I18n.t("helpers.titles.#{current_action}", :model => Model_class.model_name.human), questions_path

    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @questions }
    end
  end

  # GET /questions/1
  # GET /questions/1.json
  def show
    @question = Question.find(params[:id])

    breadcrumbs.add I18n.t("helpers.titles.#{current_action}", :model => Model_class.model_name.human), question_path(@question)

    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @question }
    end
  end

  # GET /questions/new
  # GET /questions/new.json
  def new
    @question = Question.new
    @identities  = Identity.all
    @timelines = Timeline.all
    @categories   = Category.all

    breadcrumbs.add I18n.t("helpers.titles.#{current_action}", :model => Model_class.model_name.human), new_question_path

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @question }
    end
  end

  # GET /questions/1/edit
  def edit
    @question = Question.find(params[:id])
    @identities  = Identity.all
    @timelines = []
    @categories = []

    @question_identities =  []
    if @question.identities.present?
      @question.identities.each do |identity|
        identity = Identity.find_by_name(identity.name)
        @question_identities.push(identity)
      end
    end

    @question_timelines = []
    @question.timelines.each do |timeline|
      #timeline = Timeline.find_by_name(timeline.name)
      Timeline.where(name: timeline.name).each do |t|
        @question_timelines.push(t) if @question_identities.include? t.parent
      end
    end

    @question_categories = []
      @question.categories.each do |category|
        #category = Category.find_by_name(category.name)
        Category.where(name: category.name).each do |c|
          @question_categories.push(c) if @question_timelines.include? c.parent
        end
      end

    if @question_identities.present?
      @question_identities.each do |identity|
        identity = Identity.find_by_name(identity.name)
        @timelines += identity.children.all if identity.present?
      end
    end

    if @question_timelines.present?
      @question_timelines.each do |timeline|
        Timeline.where(name: timeline.name).each do |t|
          @categories += t.children.all if @question_identities.include? t.parent
        end
      end
    end

    breadcrumbs.add I18n.t("helpers.titles.#{current_action}", :model => Model_class.model_name.human), edit_question_path
  end

  # POST /questions
  # POST /questions.json
  def create
    @question = Question.new(params[:question])
    @question.if_soft_deleted(params[:question][:soft_deleted],current_user) if params[:question][:soft_deleted].present?

    #params[:question][:identity_list].collect!{|i| Identity.find(i) if Identity.exists? i}.compact! if params[:question][:identity_list].present?
    #params[:question][:timeline_list].collect!{|t| Timeline.find(t) if Timeline.exists? t}.compact! if params[:question][:timeline_list].present?
    #params[:question][:category_list].collect!{|c| Category.find(c) if Category.exists? c}.compact! if params[:question][:category_list].present?
    params[:question][:identity_list] = Identity.find(params[:question][:identity_list]) if Identity.exists?  params[:question][:identity_list] if params[:question][:identity_list].present?
    params[:question][:timeline_list] = Timeline.find(params[:question][:timeline_list]) if Timeline.exists?  params[:question][:timeline_list] if params[:question][:timeline_list].present?
    params[:question][:category_list] = Category.find(params[:question][:category_list]) if Category.exists? params[:question][:category_list] if params[:question][:category_list].present?

    respond_to do |format|
      if @question.save
        format.html { redirect_to @question, notice: 'Question was successfully created.' }
        format.json { render json: @question, status: :created, location: @question }
      else
        format.html { render action: "new" }
        format.json { render json: @question.errors, status: :unprocessable_entity }
      end
    end
  end

  # PUT /questions/1
  # PUT /questions/1.json
  def update
    @question = Question.find(params[:id])

    #params[:question][:identity_list].collect!{|i| Identity.find(i) if Identity.exists? i}.compact! if params[:question][:identity_list].present?
    #params[:question][:timeline_list].collect!{|t| Timeline.find(t) if Timeline.exists? t}.compact! if params[:question][:timeline_list].present?
    #params[:question][:category_list].collect!{|c| Category.find(c) if Category.exists? c}.compact! if params[:question][:category_list].present?
    params[:question][:identity_list] = Identity.find(params[:question][:identity_list]) if Identity.exists?  params[:question][:identity_list] if params[:question][:identity_list].present?
    params[:question][:timeline_list] = Timeline.find(params[:question][:timeline_list]) if Timeline.exists?  params[:question][:timeline_list] if params[:question][:timeline_list].present?
    params[:question][:category_list] = Category.find(params[:question][:category_list]) if Category.exists? params[:question][:category_list] if params[:question][:category_list].present?

    @question.if_soft_deleted(params[:question][:soft_deleted],current_user) if params[:question][:soft_deleted].present?

    respond_to do |format|
      if @question.update_attributes(params[:question])
        format.html { redirect_to @question, notice: 'Question was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @question.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /questions/1
  # DELETE /questions/1.json
  def destroy
    @question = Question.find(params[:id])
    @question.destroy

    respond_to do |format|
      format.html { redirect_to questions_url }
      format.json { head :no_content }
    end
  end

  #question_list = [1,2,3]
  def resetscore
    if params.has_key? :question_list
      question_list = params[:question_list]
      select_questions = Question.where id: question_list
    else
      select_questions = Question.all
    end

    select_questions.each do |question|
      question.score = 0
      question.save
    end

    redirect_to questions_url
  end

  def update_timelines
    # updates identity and timelines based on genre selected
    identity = Identity.find(params[:identity_id])
    timelines = identity.children.all
    categories = []

    render :update do |page|
      page.replace_html 'timeline_list', :partial => 'timelines', :object => timelines
      page.replace_html 'category_list',   :partial => 'categories',   :object => categories
    end
  end

  def update_categories
    # updates categories based on timeline selected
    timeline = Timeline.find(params[:timeline_id])
    categories  = timeline.children.all

    render :update do |page|
      page.replace_html 'category_list', :partial => 'categories', :object => categories
    end
  end
end

routes.rb

  resources :questions do
    collection do
      get 'resetscore'
      match 'update_timelines'
      match 'update_categories'
    end
    resources :answers
  end

MarkUsProject/Markus#603
http://stackoverflow.com/questions/3332474/how-to-make-ajax-calls-with-rails-3-using-remote-function
In rails 3.1 and onward, its preferred to use unobstructive javascript instead of remote_function calls. The call to remote_function just generates an Ajax request so it can be replaced by an inline Ajax request. These calls occur in many places across the code base, so someone could look into changing all occurrences at once.

* so I will rewrite the demo with jQuery ...*