simple_cache.rb

# A simple expiring cache suitable for use with the PStore store.
#
# Usage:
#   SimpleCache.fetch('my_data', 15.minutes) do
#     MyModel.expensive_query
#   end
#

require 'pstore'

module SimpleCache
  CACHE_FILE = "#{Rails.root}/tmp/simple_cache"
  
  # Choose a cache_key and expiration time (e.g. 15.minutes), and pass a
  # block that returns the data you want to cache. The block will only be
  # evaluated if the cache has expired.
  def self.fetch(cache_key, expires_in)
    store = PStore.new(CACHE_FILE)
    
    data = nil
    store.transaction do
      data = store[cache_key]
    end
    
    if !data || data[:inserted_at] <  expires_in.ago.utc
      value = yield
      store.transaction do
        store[cache_key] = {
          :inserted_at => Time.now.utc,
          :value => value
        }
      end
      return value
    else
      return data[:value]
    end
  end
end