OfflineSweeper
==============

I have this problem.  We use the Rails fragment cache a lot, and we
use Sweepers to expire the cache when models are changed.  We have a
lot of cache invalidation logic in our sweepers.  Sweepers work great
when you use them the way they are expected to be used: inside
controllers.

But over time we've added background jobs fired from cron or DJ or
email (even a chat bot) that make changes to the same models that our
sweepers are supposed to be sweeping.  As some people have noticed,
sweepers quietly don't work unless the model is changed inside a web
request.

There appear to be these problems that prevent sweepers from expiring
the fragment cache inside e.g. a cron job:

* If you use a hash as your fragment cache key, Rails wants to use the
  full URL of the incoming request (indirectly through url_for) as
  part of the generated key string.  This is a problem because the
  background job doesn't have a request and because it doesn't
  necessarily know what hostname/port was used to create the fragment

* Sweepers aren't loaded and run automatically like other Observers
  outside of a controller request?

* Even if you call them explictly the sweeper will silently do nothing
  without a controller (the method_missing thing in sweeping.rb)

Action caching isn't really a problem for me so it isn't supported
yet.  There appears to be some handwringing in the code about formats
that I don't want to dig into now.

Example
=======

Example goes here.


Copyright (c) 2010 Matt Gleeson, released under the MIT license