Rails Cacheable Concern

cacheable.rb

# Rails concern that tracks and purges cache keys to avoid using Rails.cache.delete_matched since its very costly on Redis.
#
# @countries = Country.query_cached('countries:index', "limit:#{@limit}", "offset:#{@offset}") do
#  query.limit(@limit).offset(@offset).all.to_a      
# end
module Cacheable
  extend ActiveSupport::Concern

  included do
    before_save :purge_cache
    before_destroy :purge_cache
  end

  class_methods do
    def find_cached(id)
      Rails.cache.fetch(find_cached_key(id), skip_nil: true) do 
        find(id)
      end
    end  

    def find_cached_key(id)
      "#{model_name.cache_key}/#{id}/find_cached"
    end

    def query_cached(*keys, &block)
      unless query_cached_keys.include?(query_cached_key(keys))
        query_cached_keys << query_cached_key(keys)
        Rails.cache.write(query_cached_keys_key, query_cached_keys)
      end
      Rails.cache.fetch(query_cached_key(keys), skip_nil: true) do
        block.call
      end
    end  

    def query_cached_key(*keys)
      "#{model_name.cache_key}/query_cached/#{keys.join("/")}"
    end

    def query_cached_keys_key
      "#{model_name.cache_key}/query_cached_keys"
    end
    
    def query_cached_keys
      @query_cached_keys ||= Rails.cache.read(query_cached_keys_key, skip_nil: true) || []
    end

    def purge_cache
      find_each do |record|
        record.purge_cache
      end  
    end

  end  

  def find_cached_key
    @find_cached_key ||= self.class.find_cached_key(id)
  end

  def purge_cache
    starting = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    Rails.cache.delete(self.class.find_cached_key(id))
    if self.class.query_cached_keys.present?
      # TODO use Rails.cache.delete_multi after upgrading to Rails 6.1
      # Rails.cache.delete_multi(self.class.query_cached_keys)
      self.class.query_cached_keys.each do |query_cached_key|
        Rails.cache.delete(query_cached_key)
      end  
      Rails.cache.delete(self.class.query_cached_keys_key)
      Rails.cache.delete_match
    end
    ending = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    Rails.logger.debug "#{self.class.name}#purge_cache #{ending - starting} seconds"
    return true
  end 

  def query_cached(*keys, &block)
    Rails.cache.fetch("#{self.cache_key_with_version}/#{keys.join("/")}") do
      block.call
    end  
  end  

end