Q:

Javascript to assign ruby on rails form value

I am trying to get a script to assign the value of product_id when the form is submitted.  My script now always assigns the value as 1.  I need it to assign the product_id of the product.  I have noticed that when I submit it will actually change the selection to the one that is equal to id 1, so did I mess up the script where it rewrites to 1? 
Here is a JSFiddle where it seems to work fine there in html but not in my ruby code. 
Script:
$(function(){
$("#commit").on("click", function(){
    var valueAssigned = false;
    $('select').each(function(){
        if($(this).val())
        {
            $("[name='question[product_id]']").val($(this).val());
            valueAssigned = true;
            return;
        }
    });
});
});

Form: Note that only one of the collection_select is shown based on the category selected.  A script shows and hides them based on the selection. 
<%= form_for @question, url: new_tf_question_path(@question) do |f| %>

<%= render 'shared/error_questions' %>

<%= f.label :category %><br>
<%= f.select :category, [ ["IP Voice Telephony", "ip_voice"], ["IP Video Surveillance", "ip_video_surveillance"], ["IP Video Telephony", "ip_video_telephony"], ["Enterprise Gateways", "enterprise_gateways"], ["Consumer ATAs", "consumer_atas"], ["IP PBX", "ip_pbx"] ], {prompt: "Select Category"}, class: "input-lg", :id => "category" %>

<div id="ip_voice">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "ip_voice" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id1", name: "voice"} %>
</div>

<div id="ip_video_surveillance">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "ip_video_surveillance" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id2", name: "surv"} %>
</div>

<div id="ip_video_telephony">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "ip_video_telephony" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id2", name: "video"} %>
</div>

<div id="consumer_atas">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "consumer_atas" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id3", name: "atas"} %>
</div>

<div id="enterprise_gateways">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "enterprise_gateways" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id4", name: "gate"} %>
</div>

<div id="ip_pbx">
<%= f.label :product_id %><br>
<%= f.collection_select :product_id, Product.where({ category: "ip_pbx" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id5", name: "pbx"} %>
</div>

<input id="targetField" type="hidden" name="question[product_id]" value="0"/>

<%= f.label :section %><br>
<%= f.collection_select :section, @sections, :id, :name, {prompt: "Select a section"}, {class: "form-control input-lg" } %>

<%= f.label :active %><br>
<%= f.check_box :active %>

<%= f.fields_for :answers do |builder| %>

<%= render 'tf_answers', :f => builder %>

<% end %>

<%= f.submit "Create Question", class: "btn btn-lg btn-primary", id: "commit", style: "margin-top: 45px;" %>

<% end %>

I am not skilled in javascript so any help is appreciated. 
EDIT
QuestionController
def new
@question = Question.new    
@products = Product.all
end
def new_mc
@sections = Section.all
@question = Question.new
4.times { @question.answers.build }
end
def new_tf
@sections = Section.all
@question = Question.new
@question.answers.build
end

# GET /questions/1/edit
def edit
@sections = Section.all
end

# POST /questions
# POST /questions.json
def create

if params[:ip_video_telephony_product_id] ! = nil
  params[:product_id] = params[:ip_video_telephony_product_id]
end
 #:enterprise_gateways_product_id, :ip_video_surveillance_product_id, :ip_voice_product_id, :consumer_atas_product_id
@question = Question.new(question_params + params[:product_id]) 
respond_to do |format|
  if @question.save
    @answer = Answer.find_by_question_id(@question.id)
    if @answer.option == "True"
      Answer.create(option: "False", question_id: @answer.question_id, correct: false)
    end
    if @answer.option == "False"
      Answer.create(option: "True", question_id: @answer.question_id, correct: false)
    end
    format.html { redirect_to @question, notice: 'Question was successfully created.' } 
    format.json { render action: 'show', status: :created, location: @question }
  else
    format.html { render action: 'new' }
    format.json { render json: @question.errors, status: :unprocessable_entity }
  end
end
end
....
def question_params
  params.require(:question).permit(:ip_video_telephony_product_id, :enterprise_gateways_product_id, :ip_video_surveillance_product_id, :ip_voice_product_id, :consumer_atas_product_id, :section, :content, :question_type, :category, :product_id, :active, :user_id, answers_attributes: [ :option, :correct, :question_id ] ). 
  merge user_id: current_user.id
end  

Log:
Started POST "/tf_question" for 127.0.0.1 at 2014-09-19 17:09:59 -0700
Processing by QuestionsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"x", "question"=>{"question_type"=>"TF", "content"=>"damn", "category"=>"ip_video_telephony", "section"=>"1", "active"=>"1", "answers_attributes"=>{"0"=>{"correct"=>"1", "option"=>"True"}}}, "voice"=>"", "surv"=>"", "video"=>"20", "atas"=>"", "gate"=>"", "pbx"=>"", "commit"=>"Create Question"}
User Load (2.6ms)  SELECT  "users".*  FROM "users"  WHERE "users". "remember_token" = 'x' LIMIT 1
(0.1ms)  begin transaction
(0.0ms)  rollback transaction
Completed 500 Internal Server Error in 23ms

New form: I only changed all of theses and removed the script. 
<div id="ip_voice">
<%= f.label :product_id %><br>
<%= f.collection_select :ip_voice_product_id, Product.where({ category: "ip_voice" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg", id: "question_product_id1", name: "voice"} %>
</div>

A:

Although I'm not in favor of your current form arrangement, but since you say that only one select would be visible, you can use the :visible selector of jQuery.  You can change your JS click handler to something like this, assuming you added a question_product_id class to all of these select elements
var value = $('select.question_product_id:visible').val();
$("[name='question[product_id]']").val(value);

However, if it was me writing such form, I wouldn't bother setting the select value using a JS code, but I would add bunch of instance attribute to the question model (e.g. ip_video_telephony_product_id) and use them for the f.collection_select :ip_video_telephony_product_id call, then in the controller or the model I figure which value I should use based on category value, something like that. 
Example
The model would be something like this
class Question < ActiveRecord::Base
   attr_accessor :ip_video_telephony_product_id, :enterprise_gateways_product_id # etc ...
end

The selects in the form should look like this
<div id="enterprise_gateways">
 <%= f.label :ip_video_telephony_product_id %><br>
 <%= f.collection_select :ip_video_telephony_product_id, Product.where({ category: "enterprise_gateways" }), :id, :name, {prompt: "Select a product"}, {class: "form-control input-lg"} %>
</div>

Since attribute names are consistent, we can do something like this in the controller (I prefer the model, but we're keeping it simple for now)
def create
  @question = Question.new(question_params)
  @question.product_id = question_params["#{question_params[:category]}_product_id"]
  # ...
end

