Adding simple scopes to search form in spree

products_controller_decorator.rb

Spree::ProductsController.class_eval do
  def index
    if params[:search]
      [:ascend_by_master_price].each do |field|
        if params[:search][field] && params[:search][field] == ''
          params[:search][field] = nil
        end
      end
    end
    @searcher = build_searcher(params)
    @products = @searcher.retrieve_products
  end
end

search_form.html.erb

            <%= form_tag spree.products_path, :method => :get, :class => "search_form" do %>
              <%= search_field_tag :keywords, params[:keywords], :placeholder => "Search product, artist, cause" %>
              <% if params[:search] && params[:search][:ascend_by_master_price] %>
                <%= hidden_field_tag "search[ascend_by_master_price]", 
                  params[:search][:ascend_by_master_price], id: 'sort_by_field' %>
              <% end %>
            <% end %>