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This plugin is deprecated. Please upgrade your Rails installation to at least 2.1 to get this functionality, maintained, as well as all the other joys that come with a Rails upgrade.


When adds :if and :unless conditions to ActiveRecord callbacks and validations and ActionController filters. It works exactly the way as the current implementation of #validates_acceptance_of.

It works on the 12 regular callbacks:

  • before_validation

  • before_validation_on_create

  • after_validation

  • after_validation_on_create

  • before_save

  • before_create

  • before_update

  • after_create

  • after_update

  • after_save

  • before_destroy

  • after_destroy

3 validations:

  • validate

  • validate_on_create

  • validate_on_update

and 1 filter:

  • before_filter

It works when :if or :unless is passed a Symbol, a Proc or a String. They return or evaluate to a true or false value.


class Address < ActiveRecord::Base

  before_save :geolocate

  def geolocate
    if complete?

  def complete?
    street? && city? && state? && zip?


In this case, we want to find the latitude and longitude of an address only if the address is complete.

Wrapping the entirety of a callback method with conditional logic is bad form. The callback should execute WHEN the model's life cycle reaches its “before_save” point and WHEN its address is “complete.”

With When, the WHEN responsibility is moved to where it belongs: as part of the callback.

class Address < ActiveRecord::Base

  before_save :geolocate, 
    :if => :complete?

  def geolocate

  def complete?
    street? && city? && state? && zip?


before_create's single responsibility is to execute code WHEN certain conditions are met. geolocate's single responsibility is to … geolocate. It should not contain its own preconditions.

More Examples

before_create :encrypt_password,
  :unless => lambda {|user| user.password_confirmation.blank?}

before_filter :log_in!,
  :only => [:new, :create],
  :unless => :logged_in?

What When does NOT support

# ActiveRecord Class callbacks
before_create PasswordEncryptor,
  :unless => lambda {|user| user.password_confirmation.blank?}

# ActionController Class filters
before_filter Authorizer,
  :unless => :logged_in?

When will not work if your code contains any of these.

In our experience we've never used class callbacks or filters and find them to be overkill.

Obsolete after Rails 2.0.3

Whenever the next release after Rails 2.0.2 comes out, this feature will be baked into Rails via the ActiveSupport::Callbacks module. Happy coding!


piston import vendor/plugins/when


Copyright © 2008 Jared Carroll, Dan Croak, and thoughtbot, inc. released under the MIT license