ActiveModel::Observer
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. Mongoid’s observers work similar to ActiveRecord’s. Example:
class CommentObserver < Mongoid::Observer def after_save(comment) Notifications.comment( "admin@do.com", "New comment was posted", comment ).deliver end end
This Observer sends an email when a Comment#save is finished.
class ContactObserver < Mongoid::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 < Mongoid::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 < Mongoid::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.
after_initialize
before_validation
after_validation
before_create
around_create
after_create
before_update
around_update
after_update
before_save
around_save
after_save
before_destroy
around_destroy
after_destroy
If you’re using Mongoid within Rails, observer classes are usually stored in app/models with the naming convention of app/models/audit_observer.rb.
In order to activate an observer, list it in the config.mongoid.observers configuration setting in your config/application.rb file.
config.mongoid.observers = :comment_observer, :signup_observer
Observers will not be invoked unless you define them in your application configuration.
Observers register themselves with the model class that they observe, since it is the class that notifies them of events when they occur. As a side-effect, when an observer is loaded, its corresponding model class is loaded.
Observers are loaded after the application initializers, so that observed models can make use of extensions. If by any chance you are using observed models in the initialization, you can still load their observers by calling ModelObserver.instance before. Observers are singletons and that call instantiates and registers them.
Adds the specified observer to the class.
@example Add the observer.
observer.add_observer!(Document)
@param [ Class ] klass The child observer to add.
@since 2.0.0.rc.8
# File lib/mongoid/observer.rb, line 141 def add_observer!(klass) super and define_callbacks(klass) end
Defines all the callbacks for each observer of the model.
@example Define all the callbacks.
observer.define_callbacks(Document)
@param [ Class ] klass The model to define them on.
@since 2.0.0.rc.8
# File lib/mongoid/observer.rb, line 153 def define_callbacks(klass) tap do |observer| observer_name = observer.class.name.underscore.gsub('/', '__') Mongoid::Callbacks::CALLBACKS.each do |callback| next unless respond_to?(callback) callback_meth = :"_notify_#{observer_name}_for_#{callback}" unless klass.respond_to?(callback_meth) klass.send(:define_method, callback_meth) do |&block| observer.send(callback, self, &block) end klass.send(callback, callback_meth) end end end end
Get all the child observers.
@example Get the children.
observer.observed_descendants
@return [ Array<Class> ] The children.
@since 2.0.0.rc.8
# File lib/mongoid/observer.rb, line 129 def observed_descendants observed_classes.sum([]) { |klass| klass.descendants } end
Instantiate the new observer. Will add all child observers as well.
@example Instantiate the observer.
Mongoid::Observer.new
@since 2.0.0.rc.8
# File lib/mongoid/observer.rb, line 115 def initialize super and observed_descendants.each { |klass| add_observer!(klass) } end
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