redrecord

---

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

Example

---

class User < ActiveRecord::Base

  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

  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

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