Class: ActiveModel::Observer
- Inherits:
-
Object
- Object
- ActiveModel::Observer
- Extended by:
- ActiveSupport::DescendantsTracker
- Includes:
- Singleton
- Defined in:
- lib/rails/observers/active_model/observing.rb
Overview
Active Model Observers
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.
class CommentObserver < ActiveModel::Observer
def after_save(comment)
Notifications.comment('[email protected]', 'New comment was posted', comment).deliver
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.
Observing a class that can’t be inferred
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.
If you’re using an Observer in a Rails application with Active Record, be sure to read about the necessary configuration in the documentation for ActiveRecord::Observer.
Direct Known Subclasses
Class Method Summary collapse
-
.observe(*models) ⇒ Object
Attaches the observer to the supplied model classes.
-
.observed_class ⇒ Object
Returns the class observed by default.
-
.observed_classes ⇒ Object
Returns an array of Classes to observe.
Instance Method Summary collapse
-
#initialize ⇒ Observer
constructor
Start observing the declared classes and their subclasses.
-
#observed_class_inherited(subclass) ⇒ Object
Special method sent by the observed class when it is inherited.
-
#observed_classes ⇒ Object
:nodoc:.
-
#update(observed_method, object, *extra_args, &block) ⇒ Object
Send observed_method(object) if the method exists and the observer is enabled for the given object’s class.
Constructor Details
#initialize ⇒ Observer
Start observing the declared classes and their subclasses. Called automatically by the instance method.
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# File 'lib/rails/observers/active_model/observing.rb', line 340 def initialize #:nodoc: observed_classes.each { |klass| add_observer!(klass) } end |
Class Method Details
.observe(*models) ⇒ Object
Attaches the observer to the supplied model classes.
class AuditObserver < ActiveModel::Observer
observe :account, :balance
end
AuditObserver.observed_classes # => [Account, Balance]
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# File 'lib/rails/observers/active_model/observing.rb', line 307 def observe(*models) models.flatten! models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model } singleton_class.redefine_method(:observed_classes) { models } end |
.observed_class ⇒ Object
Returns the class observed by default. It’s inferred from the observer’s class name.
PersonObserver.observed_class # => Person
AccountObserver.observed_class # => Account
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# File 'lib/rails/observers/active_model/observing.rb', line 333 def observed_class name[/(.*)Observer/, 1].try :constantize end |
.observed_classes ⇒ Object
Returns an array of Classes to observe.
AccountObserver.observed_classes # => [Account]
You can override this instead of using the observe
helper.
class AuditObserver < ActiveModel::Observer
def self.observed_classes
[Account, Balance]
end
end
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# File 'lib/rails/observers/active_model/observing.rb', line 324 def observed_classes Array(observed_class) end |
Instance Method Details
#observed_class_inherited(subclass) ⇒ Object
Special method sent by the observed class when it is inherited. Passes the new subclass.
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# File 'lib/rails/observers/active_model/observing.rb', line 357 def observed_class_inherited(subclass) #:nodoc: self.class.observe(observed_classes + [subclass]) add_observer!(subclass) end |
#observed_classes ⇒ Object
:nodoc:
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# File 'lib/rails/observers/active_model/observing.rb', line 344 def observed_classes #:nodoc: self.class.observed_classes end |
#update(observed_method, object, *extra_args, &block) ⇒ Object
Send observed_method(object) if the method exists and the observer is enabled for the given object’s class.
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# File 'lib/rails/observers/active_model/observing.rb', line 350 def update(observed_method, object, *extra_args, &block) #:nodoc: return if !respond_to?(observed_method) || disabled_for?(object) send(observed_method, object, *extra_args, &block) end |