Simple, global ActiveRecord event observers, using a middleware architecture, that can easily be turned on and off. Designed for audit trails, activity feeds and other application-level event handlers.
gem install active_model_listener
First, require Active Model Listener above your rails initializer:
# environment.rb require 'active_model_listener' Rails::Initializer.run do |config| # ... end
Add the listeners to the ActiveModelListener in an initializer:
# config/initializers/active_model_listener.rb . << ActivityFeedListener
NOTE: you can also use a string or symbol version of the class. The following are all equivalent:
. << ActivityFeedListener . << "ActivityFeedListener" . << "activity_feed_listener" . << :activity_feed_listener
Then, create a listener class that defines methods for after_create, after_update and/or after_destroy:
class ActivityFeedListener class << self def after_create(record) # do stuff end def after_update(record) # do stuff end def after_destroy(record) # do stuff end end end
Inside the after_create, after_destroy and after_update methods all calls will be called without listeners, to prevent recursion. If you need listeners to be turned on during those blocks, you'll have to set them yourself within the blocks.
Turning off listeners in specs
When unit testing if your listeners are all firing your unit tests become integration tests. To avoid this, you can easily turn off listeners for all specs all the time:
Spec::Runner.configure do |config| config.before(:each) do ..clear end end
Then, when you want them back on again, you can either turn them back on for a spec:
describe "Integrating with listeners" do before do . << FooListener end end
Specifying a subset of listeners to use
When doing data imports, migrations or certain actions that need to only use certain listeners, you can easily specify which ones you'd like to use:
. AuditListener, ActivityListener do Article.create! :title => "foo" end
After the block runs, the original listeners are restored.
If you want to run some code with no listeners, you can do so with:
. do Article.create! :title => "foo" end
Um. Don't observers already do this?
ActiveRecord Observers are:
- Hard to apply to large numbers of models (you have to explicitly declare every one)
- Hard to turn off in tests
- Hard to selectively enable / disable
ActiveModelListener applies to all ActiveRecord models anywhere in your app, all the time. ActiveModelListener listeners are very easy to turn off during unit tests as well.
Copyright (c) 2009 Jeff Dean. See LICENSE for details.