cache_proxy.rb

# lib/cache_proxy.rb

class CacheProxy
  class << self
    attr_accessor :cache
  end

  def initialize(obj)
    @obj = obj
  end

  def cache_key(meth)
    "#{self.class}:#{@obj.class}:#{@obj.object_id}:#{meth}"
  end

  def cache_fetch(meth, *args, &block)
    key = cache_key(meth)
    self.class.cache.cache_fetch(key, expires_in: 1.hour) do
      @obj.__send__(meth, *args, &block)
    end
  end

  def method_missing(meth, *args, &block)
    if @obj.respond_to?(meth)
      cache_fetch(meth, *args, &block)
    else
      super
    end
  end
end


module CacheProxyMethods
  def cached
    CacheProxy.new(self)
  end
end

cache_proxy_initializer.rb

# config/initializers/cache_proxy.rb

require 'cache_proxy'

ActiveSupport.on_load(:redis) do
  CacheProxy.cache = $redis
  ActiveRecord::Base.send(:include, CacheProxyMethods)
end

redis.rb

# config/initializers/redis.rb

$redis = Redis.new

class << $redis
  # Include client helper extensions, which implement cache_fetch among others
  include RedisClientExtensions
end

ActiveSupport.run_load_hooks(:redis, self)

redis_client_extensions.rb

module RedisClientExtensions

  # Get/set a value cached in a key
  #
  # key - String key name
  # expires_in: Integer TTL of the key, in seconds
  # block - Proc to compute the value to be cached on miss
  #
  # Returns result of evaluating <block>
  def cache_fetch(key, expires_in:, &block)
    if ret = get(key)
      ret
    else
      val = block.call
      set(key, val)
      expire(key, expires_in)
      val
    end
  end

end

An experiment to transparently cache methods independent of their implementation. Example:

val = my_object.cached.expensive_computation # Stores value in cache
...
object.cached.expensive_computation # Retrieves from cache - doesn't actually call method!

Calling cached on an object will return a corresponding CacheProxy:

Post.last.cached
#<CacheProxy:0x007f9a04d65420 @obj=#<Post ...>"

Calling methods on this cache proxy will first check the cache for a value, and only call the actual method if a value is missing. Note this is accomplished using the cache_fetch method on the configurable cache backend, which is responsible for implementing this (we've added the cache_fetch method to the Redis client, although any interface that implements cache_fetch will do)