I have the following scenario:

    class Product < ActiveRecord::Base
        belongs_to :categories

    class Category < ActiveRecord::Base
        has_many :products

Categories table has 2 level nesting, for example. Main category is 'Men', sub-category is 'Accessories' and sub-sub-category is 'Watches'. enter image description here

Now when user creates new product he must choose category(only main category is required, but he can also chose sub and sub-sub category optional).

My idea is this: I created 3 different select boxes with same name "product[category_id]", so only the last selected value will be sent to the server through params[:product][:category_id].

<div class="col-md-2 main-category">
    <small> Main category? required </small>
    <%= f.select :category_id, 
            Category.where('category_id IS ?', nil).collect {|c| [c.name, c.id]},
            { include_blank: "Select category..." }, 
            id: 'main-category', class: 'form-control' %>
<div class="col-md-2 category-level-1">
    <small> What type? optional </small>
    <%= f.select :category_id, {}, {}, class: 'form-control' %>

<div class="col-md-2 category-level-2">
    <small> What type? optional </small>
    <%= f.select :category_id, {}, {}, class: 'form-control' %>

2nd(sub-categories) and 3rd(sub-sub-categories) are initial empty ({}, {}) and hidden through CSS(display: none) and will be populated through Ajax call.

$('#main-category, .category-level-1 > select').change(function() {
    var selectBox = this.id;
    var selectedValue = $(this).val();
    var url = '/categories/' + selectedValue + '/subcategories';

    $.get(url, function(data) { createSelect(data, selectBox); });

function createSelect(data, selectBox) {
  var $currentSelect = null;

  if (selectBox == 'main-category') {
    $('.category-level-1 > select').find('option').remove();

    $currentSelect = $('.category-level-1 > select');
  else {
    $('.category-level-2 > select').find('option').remove();

    $currentSelect = $('.category-level-2 > select');

  $currentSelect.append('<option selected disabled>Select Category...</option>');
  for(var i=0; i<data.length; i++) {
    $currentSelect.append('<option value="' + data[i].id + '">' + data[i].name +

Where Ajax call is sent to following route (categories controller)

def subcategories
    id = params[:id]
    @subcategories = Category.where('category_id = ?', id)
    render json: @subcategories 

So for final result i have following: enter image description here

First of all, is it normal to have different inputs in one form with same names created manually like I did in this example? For some reason, it seem like 'code-smell' to me. I'm relatively new to Rails, so I wanted to ask if I am violating some good practices with this code. Can you suggest better ways of achieving the same results?


1 Answer 1


These are nested selects, you can try awesome_nested_set, and use it like this:

<%= f.select :parent_id, 
             nested_set_options(Category, @category) {|i| "#{'-' * i.level} #{i.name}" } %>

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