redrecord

This gem pre-caches your ActiveRecord model's calculated attributes (computed fields) in Redis.

Example

class User < ActiveRecord::Base

redis_cache do
 def fullname
   firstname + ' ' + lastname
 end
end

end

Methods defined inside the "cache" block are redefined to get the answer from redis first. The cached attributes are saved whenever the record is saved, in an after_commit callback.

Cache invalidation for associations

Redrecord can be used to cache attributes that use assocations:

class User < ActiveRecord::Base has_many :preferences

redis_cache do
 def preferences_list
   preferences.map(&:name).join(', ')
 end
end

end

class Preference < ActiveRecord::Base belongs_to :user

invalidate_cache_on :user

end

In this example, whenever a preference is saved, the associated user record will be recalculated and saved in redis. If it is an array (eg. has_many) then all of the associated records will be re-cached.

Other instance methods of interest:

obj.remove_from_cache! # Remove redis cache for an object. obj.add_to_cache! # Recalculate fields and store in redis. obj.cached_fields # hash of the cached fields and their values obj.attribs_with_cached_fields # cached_fields merged with AR attributes obj.verify_cache! # raise an error if cache doesn't match calculated

If redis is down?

To enable talking to a redis server, set Redrecord.enabled=true

If Redrecord can't access redis within a timeout (Redrecord.timeout=15 by default) then it sets enabled=false, disabling all redis access so your application can keep working without the cache.

For testing purposes, you can set Redrecord.write_only = true This keeps the cache contents up to date but does not read back any cached content.

Setup

in your Gemfile:

gem 'redrecord'

in your rails app config/initializers/redrecord.rb:

$redis = Redis.new(:host => 'localhost', :port => 6379, :db => 1)
Redrecord.redis = $redis
Redrecord.enabled = true

Contact the author

Andrew Snow andrew@modulus.org Andys^ on irc.freenode.net