Different selects in one form with same name attribute?

[Srdjan Cengic]

Question are at end of the topic.

class Product < ActiveRecord::Base
    belongs_to :categories
end

class Category < ActiveRecord::Base
    has_many :products
end

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

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 following: 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>

<div class="col-md-2 category-level-1">
    <small> What type? optional </small>
    <%= f.select :category_id, {}, {}, class: 'form-control' %>
</div>

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

For populating 2nd select(sub-category) and 3rd(sub-sub-categories) i'm using ajax call where 2nd and 3rd select are initial hidden (display: none) through CSS.

$('#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').show();
    $('.category-level-2').hide();
    $('.category-level-1 > select').find('option').remove();

    $currentSelect = $('.category-level-1 > select');
  }
  else {
    $('.category-level-2').show();
    $('.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 + '</option>');
  }
}

Where ajax call is sent to following route (categories controller)
def subcategories
    id = params[:id]
    @subcategories = Category.where('category_id = ?', id)
    render json: @subcategories 
end

So for final result i have following:

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 wanted to ask am'i violating some good practices with this code?Can you suggest better way to achieve same results?Thanks.