How to update counter_cache when updating a model?

I have a very simple relationship - a container has many items

containers(title, items_count) items(container_id, title)

class Item < ActiveRecord::Base   belongs_to :container, :counter_cache => true end

My views/items/edit.html.erb looks like this: <p>   <%= f.label :assign_to_container %>   <%= f.collection_select :container_id, Container.all, :id, :title %> </p>

And my items_controller.rb looks like this:

class ItemsController < ApplicationController   def edit     @item = Item.find(params[:id])   end

  def update     @item = Item.find(params[:id])     if @item.update_attributes params[:item]       flash[:notice] = "Item updated"       redirect_to items_path     else       render :action => :edit     end   end end

My problem is that the counter cache (container.items_count) is not getting updated when I update an item's container. Anyone know what I'm doing wrong? I'm on Rails 2.3.5

p.s. I got it to "work" by add this to my update action, but it seems like there should be a cleaner solution

  def update     @item = Item.find(params[:id])     @item.container = Container.find(params[:item][:container_id]) unless params[:item][:container_id].blank?     if @item.update_attributes params[:item]       flash[:notice] = "Item updated"       redirect_to items_path     else       render :action => :edit     end   end