Rails page cache sweeping

Fwoosh fwoosh.  Caching is easy.  Expiring those caches on the other hand can drive you absolutely crazy.

Two things I've learned.

Expiring the cache when your Model is used in a single monolithic pattern is a piece of cake.  Following any standard documentation is easy peasy.

However, one of my Models generates an N number of directories and files dependent on the user's setup.

For example, SiteA can have About Us, FAQ, and Contacts as directories with a number of db served pages for each that are cached.

After many many failed attempts here's what I've learned:

1. You must setup in config/application.rb the config.active_record.observers = :observer or it will never be found.
2. Sweepers need to be explicitly told which model to observe "observe :model"
3. use of {page.cache.directory} needs to be more explicit with  "#{ActionController::Base.page_cache_directory}"
4. For situations where mass numbers of pages need to be expired simultaneously, be very careful in the use of FileUtils.rm_rf improper usage can blow up your file system.

The last one was a tip learned from the venerable Ryan Bates of Railscasts fame -- of course I'm a subscriber. 

Additionally, when I had a Model that generated a single directory with n number of pages inside such as when caching a paged view, the solution was to do:

FileUtils.rm_rf "#{ActionController::Base.page_cache_directory}/directory"

But I had one model that produced an unknown number of pages.  At first I wanted to hard code the directory structure by copy and pasting the above line changing the final directory.  But that's just stupid.  I've learned that every time I found myself hacking out that pattern that I needed to stop, and rethink the problem.

Since the problem was DB generated, the solution had to be as well.

I simply yanked out all the pathnames from the db and rm -rf each of those.

Model.all.each do |page|
  FileUtils.rm_rf "#{ActionController::Base.page_cache_directory}/#{page.path}"
end