Object
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. Example:
class CommentObserver < ActiveModel::Observer def after_save(comment) Notifications.deliver_comment("admin@do.com", "New comment was posted", comment) end end
This Observer sends an email when a Comment#save is finished.
class ContactObserver < ActiveModel::Observer def after_create(contact) contact.logger.info('New contact added!') end def after_destroy(contact) contact.logger.warn("Contact with an id of #{contact.id} was destroyed!") end end
This Observer uses logger to log when specific callbacks are triggered.
Observers will by default be mapped to the class with which they share a name. So CommentObserver will be tied to observing Comment, ProductManagerObserver to ProductManager, and so on. If you want to name your observer differently than the class you’re interested in observing, you can use the Observer.observe class method which takes either the concrete class (Product) or a symbol for that class (:product):
class AuditObserver < ActiveModel::Observer observe :account def after_update(account) AuditTrail.new(account, "UPDATED") end end
If the audit observer needs to watch more than one kind of object, this can be specified with multiple arguments:
class AuditObserver < ActiveModel::Observer observe :account, :balance def after_update(record) AuditTrail.new(record, "UPDATED") end end
The AuditObserver will now act on both updates to Account and Balance by treating them both as records.
Start observing the declared classes and their subclasses.
# File lib/active_model/observing.rb, line 190 190: def initialize 191: observed_classes.each { |klass| add_observer!(klass) } 192: end
Attaches the observer to the supplied model classes.
# File lib/active_model/observing.rb, line 158 158: def observe(*models) 159: models.flatten! 160: models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model } 161: remove_possible_method(:observed_classes) 162: define_method(:observed_classes) { models } 163: end
The class observed by default is inferred from the observer’s class name:
assert_equal Person, PersonObserver.observed_class
# File lib/active_model/observing.rb, line 180 180: def observed_class 181: if observed_class_name = name[/(.*)Observer/, 1] 182: observed_class_name.constantize 183: else 184: nil 185: end 186: end
Returns an array of Classes to observe.
You can override this instead of using the observe helper.
class AuditObserver < ActiveModel::Observer def self.observed_classes [Account, Balance] end end
# File lib/active_model/observing.rb, line 174 174: def observed_classes 175: Array.wrap(observed_class) 176: end
Disabled; run with --debug to generate this.
Generated with the Darkfish Rdoc Generator 1.1.6.