# module ActionController::Caching::Sweeping

Sweepers are the terminators of the caching world and responsible for expiring caches when model objects change. They do this by being half-observers, half-filters and implementing callbacks for both roles. A Sweeper example:

    class ListSweeper < ActionController::Caching::Sweeper
      observe List, Item

      def after_save(record)
        list = record.is_a?(List) ? record : record.list
        expire_page(:controller => "lists", :action => %w( show public feed ), :id => list.id)
        expire_action(:controller => "lists", :action => "all")
        list.shares.each { |share| expire_page(:controller => "lists", :action => "show", :id => share.url_key) }
      end
    end

The sweeper is assigned in the controllers that wish to have its job performed using the `cache_sweeper` class method:

    class ListsController < ApplicationController
      caches_action :index, :show, :public, :feed
      cache_sweeper :list_sweeper, :only => [ :edit, :destroy, :share ]
    end

In the example above, four actions are cached and three actions are responsible for expiring those caches.

You can also name an explicit class in the declaration of a sweeper, which is needed if the sweeper is in a module:

    class ListsController < ApplicationController
      caches_action :index, :show, :public, :feed
      cache_sweeper OpenBar::Sweeper, :only => [ :edit, :destroy, :share ]
    end