VolatileCounterCache

Provides volatile counter cache logic to ActiveRecord::Base.

1. favorites_count tries to read counter cache from Rails.cache.
2. If there is no cache yet, it calls favorites.size and store the result.
3. When favorite is created or destroyed, the cache is purged.

class Tweet < ActiveRecord::Base
  has_many :favorites

  volatile_counter_cache :favorites, cache: Rails.cache
end

Tweet.first.favorites_count #=> 42
Tweet.first.favorites.first.destroy
Tweet.first.favorites_count #=> 41

• cache [ActiveSupport::Cache::Store] A store object to store count for each key.
• cache_options [Hash] Options for cache store.
• counter_method_name [String] An optional String to change counter method name.
• foreign_key [Symbol] An optional Symbol to change cache key at callback.