Rails%203%20In%20Action

456 CHAPTER 16 Basic performance enhancements
for a file, you shouldn’t see any. The directories (with names like E62 and 3E0) will
still exist, but there aren’t any files. This means that Rails has successfully cleared its
cache of fragments for the project.
Let’s get your sweeper to perform this same action when tickets are updated and
destroyed. Move the expire_fragment call into another method and then call it in the
after_create, after_update, and after_destroy methods in TicketsSweeper using
the code shown in the following listing.
class TicketsSweeper < ActionController::Caching::Sweeper
observe Ticket
def after_create(ticket)
expire_fragments_for_project(ticket.project)
end
end
Listing 16.4 app/sweepers/tickets_sweeper.rb
def after_update(ticket)
expire_fragments_for_project(ticket.project)
end
def after_destroy(ticket)
expire_fragments_for_project(ticket.project)
end
private
def expire_fragments_for_project(project)
expire_fragment(/projects\/#{project.id}\/.*?/)
end
Now you have Rails caching the pages of tickets for all projects in your application and
clearing that cache when tickets are updated. This is a great demonstration of caching
on a per-user basis, even if your project page isn’t that intensive. If you had a system
resource (CPU/memory) intensive action in your application that required user customization
like this, you could use this same method to cache that action to stop it
from being hit so often, which would reduce the strain on your server.
Expiring pages
If you were still using caches_page, you wouldn’t use expire_fragment to expire
the cache files that were generated. Instead, you’d use expire_page, which can take
a hash like this:
expire_page(:controller => "projects",
:action => "show",
:id => 1)
Or, better still would be to pass it the URL helper:
expire_page(project_path(1))
Even though you’re not caching pages any more, it’s still handy to know how to clear
cached pages and fragments.