<%= semantic_form_for [:admin, @game], builder: ActiveAdmin::FormBuilder do |f| %>
  <%= f.semantic_errors :state %>
    <%= f.inputs do %>
        <%= f.input :categorization_id, label: 'Provider', as: :select,
                    collection: Provider.all.map { |provider| ["#{provider.name}", provider.id] },
                    input_html: { class: (:provider_select), 'data-url': category_select_path(provider: 4) } %>
        <%= f.input :categorization_id, label: 'Category',input_html: { class: ('category_dropdown') }, as: :select,
                    collection: Category.all.map { |category| ["#{category.name}", category.id]}%>
        ...

    <% end %>
  <%= f.actions %>
<% end %>

controller do
  def ajax_call
      @provider = Provider.find(params[:provider])
      @categories = @provider.categories
      respond_to do |format|
        format.json { render json: @categories }
      end
    end
end

$(document).on('ready page:load', function () {

  $('.select.input.optional').last().addClass('hidden_row');

  $('#game_categorization_id').change(function () {
    var id_value = this.value;
    $('.hidden_row').removeClass('hidden_row');
    $.ajax({
      type: 'GET',
      url: '/admin/games/category_select'
      // data: id_value
    })
  });

});