Class: ActiveRecord::Observer
- Inherits:
-
Object
- Object
- ActiveRecord::Observer
- Includes:
- Singleton
- Defined in:
- lib/active_record/observer.rb
Overview
Observer classes respond to lifecycle 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 < ActiveRecord::Observer
def after_save(comment)
Notifications.deliver_comment("[email protected]", "New comment was posted", comment)
end
end
This Observer sends an email when a Comment#save is finished.
class ContactObserver < ActiveRecord::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 < ActiveRecord::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 < ActiveRecord::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.
Available callback methods
The observer can implement callback methods for each of the methods described in the Callbacks module.
Storing Observers in Rails
If you’re using Active Record within Rails, observer classes are usually stored in app/models with the naming convention of app/models/audit_observer.rb.
Configuration
In order to activate an observer, list it in the config.active_record.observers
configuration setting in your config/environment.rb
file.
config.active_record.observers = :comment_observer, :signup_observer
Observers will not be invoked unless you define these in your application configuration.
Class Method Summary collapse
-
.observe(*models) ⇒ Object
Attaches the observer to the supplied model classes.
-
.observed_class ⇒ Object
The class observed by default is inferred from the observer’s class name: assert_equal [Person], PersonObserver.observed_class.
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.
-
#update(observed_method, object) ⇒ Object
Send observed_method(object) if the method exists.
Constructor Details
#initialize ⇒ Observer
Start observing the declared classes and their subclasses.
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# File 'lib/active_record/observer.rb', line 151 def initialize Set.new(observed_classes + observed_subclasses).each { |klass| add_observer! klass } end |
Class Method Details
.observe(*models) ⇒ Object
Attaches the observer to the supplied model classes.
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# File 'lib/active_record/observer.rb', line 133 def observe(*models) models.flatten! models.collect! { |model| model.is_a?(Symbol) ? model.to_s.camelize.constantize : model } define_method(:observed_classes) { Set.new(models) } end |
.observed_class ⇒ Object
The class observed by default is inferred from the observer’s class name:
assert_equal [Person], PersonObserver.observed_class
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# File 'lib/active_record/observer.rb', line 141 def observed_class if observed_class_name = name.scan(/(.*)Observer/)[0] observed_class_name[0].constantize else nil end 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/active_record/observer.rb', line 162 def observed_class_inherited(subclass) #:nodoc: self.class.observe(observed_classes + [subclass]) add_observer!(subclass) end |
#update(observed_method, object) ⇒ Object
Send observed_method(object) if the method exists.
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# File 'lib/active_record/observer.rb', line 156 def update(observed_method, object) #:nodoc: send(observed_method, object) if respond_to?(observed_method) end |