toolkit to build Rails observers (part of Rails)

 This package contains two observers: Active Record Observer and
 Action Controller Sweeper.
 .
 Active Record Observer classes respond to life cycle callbacks to
 implement trigger-like behavior outside the original class. This is a
 great way to reduce the clutter that normally comes when the model
 class is burdened with functionality that doesn't pertain to the core
 responsibility of the class.
 .
 Active Record Sweepers are the terminators of the caching world and
 responsible for expiring caches when model objects change. They do
 this by being half-observers, half-filters and implementing callbacks
 for both roles.