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.
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:
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.
Triggering Observers
In order to activate an observer, you need to call Observer.instance. In Rails, this can be done in controllers using the short-hand of for example observer :comment_observer.
Class Method Summary collapse
-
.observe(*models) ⇒ Object
Attaches the observer to the supplied model classes.
Instance Method Summary collapse
-
#initialize ⇒ Observer
constructor
A new instance of Observer.
-
#update(callback_method, object) ⇒ Object
:nodoc:.
Constructor Details
#initialize ⇒ Observer
Returns a new instance of Observer.
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# File 'lib/active_record/observer.rb', line 60 def initialize [ observed_class ].flatten.each do |klass| klass.add_observer(self) klass.send(:define_method, :after_find) unless klass.respond_to?(:after_find) end 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 56 def self.observe(*models) define_method(:observed_class) { models } end |
Instance Method Details
#update(callback_method, object) ⇒ Object
:nodoc:
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# File 'lib/active_record/observer.rb', line 67 def update(callback_method, object) #:nodoc: send(callback_method, object) if respond_to?(callback_method) end |