Can something be done better?

Can something be done better?.rb

 # AJAX request: This adds line items to cart. 
  def add_line_item_to_cart
    #Get current_cart object
    current_cart
    quantity = params[:quantity].to_i
    id = params[:id].to_i
    line_item = LineItem.find(:first, :conditions => {:cartridge_id => id, :cart_id => current_cart.id})
    #If there is line item wich maches conditions then just update quantity
    #Returns quantity with total of items in cart
    if line_item != nil
      line_item.cart_id = current_cart.id
      line_item.quantity = line_item.quantity+quantity
      line_item.save
      render :text => current_cart.line_items.count.to_s
    #If there is no line item wich maches conditions create new LineItem object and add values to it
    #Returns quantity with total of items in cart
    else
      line_item = LineItem.new
      line_item.cartridge_id = id
      line_item.cart_id = current_cart.id
      line_item.quantity = quantity
      line_item.save
      render :text => current_cart.line_items.count.to_s
    end
  end