canvas-lms/gems/activesupport-suspend_callbacks

Suspend Callbacks

ActiveSupport's Callbacks module allows you to define a callback hook and then register methods to be run before/after/around that hook.

It also let's you skip callbacks in a specific context. For example, ActiveRecord::Base defines a callback hook around save. My top level Person model may register an :ensure_privacy method to run before save. But the Celebrity model that inherits from Person can then skip that callback. End result: when I save a john_doe Person object, :ensure_privacy will run, but when I save the dhh Celebrity object, it won't.

But what if you want to suspend callbacks, regardless of subclass, but only for a duration of time? That's when you want to suspend callbacks.

Example

class MyModel < ActiveRecord::Base include ActiveSupport::Callbacks::Suspension

before :save, :expensive_callback after :save, :other_callback

def expensive_callback # stuff end

def other_callback # stuff end end

instance1 = MyModel.new instance2 = MyModel.new

MyModel.suspend_callbacks do

neither callback will run for either instance

instance1.save instance2.save end

MyModel.suspend_callbacks(kind: :save) do

same

instance1.save instance2.save end

MyModel.suspend_callbacks(:expensive_callback) do

expensive_callback won't run, but other_callback will

instance1.save instance2.save end

MyModel.suspend_callbacks(type: :before) do

same

instance1.save instance2.save end

instance1.suspend_callbacks do

callbacks won't run this time...

instance1.save

... but they will this time.

instance2.save end