Simulates Rails cache tags invalidation. Allows using cache like Rails.cache.fetch [key, tag] do .... end and Rails.cache.clear_tag tag

cache_tag_invalidation.rb

# config/initializers/cache_tag_invalidation.rb
module CacheTagInvalidation
  puts <<-WARNING
    Adding cache tag invalidation. 
    NOTICE that this will work only with MemoryStore on single process or with memcached store
  WARNING
  def write *args
    if args.first.is_a?(Array) && args.first.size == 2 # Simulate tags only whan cache key is an array of 2 elements
      key, tag = args.first
      taglist_key = ["CacheTagList", tag]
      keys = read(taglist_key) || []      
      super taglist_key, keys << key
    end
    super
  end

  def clear_tag tag
    taglist_key = ["CacheTagList", tag] 
    (read(taglist_key) || []).each do |k|
      delete [k, tag]
    end
    delete taglist_key
  end
end 
Rails.cache.extend CacheTagInvalidation