Jer on Rails

Caching ActiveRecord Objects with Rails.cache file_store

• Posted July 26th, 2008 by Jeremy Weiskotten.
• 3 comments

Rails 2.1 presents Rails.cache, a clean little interface for caching stuff. It makes it easy to switch between different cache stores. For example, we are using memcached in production but something else, like the file system, in development where performance and scalability aren’t as important as forward progress.

Memcached supports the caching of ActiveRecord objects, so you can do something simple like this:

all_things = Rails.cache.fetch('Thing.all') { Thing.all }

This single line of code looks for a cache entry by the key “Thing.all”. If it’s not found, the code in the block is executed and the results are added to the cache and returned. If that cache entry is found, the value is returned from the cache, avoiding a trip to the database. Very useful for things that rarely change.

This works great with memcached store, but not with file store, which seems to prefer simple strings. A workaround is to convert the ActiveRecord objects to YAML when putting them in the cache and converting back from YAML when reading:

all_things = YAML::load(Rails.cache.fetch('Thing.all') { Thing.all.to_yaml })

I recommend encapsulating this in a class method:


class Thing < ActiveRecord::Base
  def self.all_cached
    YAML::load(Rails.cache.fetch('Thing.all') { all.to_yaml })
  end
end