Class: ActiveModel::Observer

### Home Classes Methods

### In Files

- lib/active_model/observing.rb

### Parent

Object

### Methods

- ::new
- ::observe
- ::observed_class
- ::observed_classes
- #disabled_for?

### Included Modules

- Singleton

### Class/Module Index

Quicksearch

- ActiveModel
- ActiveModel::AttributeMethods
- ActiveModel::AttributeMethods::ClassMethods
- ActiveModel::AttributeMethods::ClassMethods::AttributeMethodMatcher
- ActiveModel::BlockValidator
- ActiveModel::Callbacks
- ActiveModel::Conversion
- ActiveModel::Dirty
- ActiveModel::EachValidator
- ActiveModel::Errors
- ActiveModel::Lint
- ActiveModel::Lint::Tests
- ActiveModel::MassAssignmentSecurity
- ActiveModel::MassAssignmentSecurity::BlackList
- ActiveModel::MassAssignmentSecurity::ClassMethods
- ActiveModel::MassAssignmentSecurity::Error
- ActiveModel::MassAssignmentSecurity::LoggerSanitizer
- ActiveModel::MassAssignmentSecurity::PermissionSet
- ActiveModel::MassAssignmentSecurity::Sanitizer
- ActiveModel::MassAssignmentSecurity::StrictSanitizer
- ActiveModel::MassAssignmentSecurity::WhiteList
- ActiveModel::MissingAttributeError
- ActiveModel::Name
- ActiveModel::Naming
- ActiveModel::Observer
- ActiveModel::ObserverArray
- ActiveModel::Observing
- ActiveModel::Observing::ClassMethods
- ActiveModel::SecurePassword
- ActiveModel::SecurePassword::ClassMethods
- ActiveModel::SecurePassword::InstanceMethodsOnActivation
- ActiveModel::Serialization
- ActiveModel::Serializers
- ActiveModel::Serializers::JSON
- ActiveModel::Serializers::Xml
- ActiveModel::StrictValidationFailed
- ActiveModel::Translation
- ActiveModel::Validations
- ActiveModel::Validations::AcceptanceValidator
- ActiveModel::Validations::Callbacks
- ActiveModel::Validations::Callbacks::ClassMethods
- ActiveModel::Validations::ClassMethods
- ActiveModel::Validations::ConfirmationValidator
- ActiveModel::Validations::ExclusionValidator
- ActiveModel::Validations::FormatValidator
- ActiveModel::Validations::HelperMethods
- ActiveModel::Validations::InclusionValidator
- ActiveModel::Validations::LengthValidator
- ActiveModel::Validations::NumericalityValidator
- ActiveModel::Validations::PresenceValidator
- ActiveModel::Validations::WithValidator
- ActiveModel::Validator

No matching classes.

# ActiveModel::Observer

## 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. Example:

    class CommentObserver < ActiveModel::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 < 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.

### Public Class Methods

new() click to toggle source

Start observing the declared classes and their subclasses.

    # File lib/active_model/observing.rb, line 218
    def initialize
      observed_classes.each { |klass| add_observer!(klass) }
    end

observe(*models) click to toggle source

Attaches the observer to the supplied model classes.

    # File lib/active_model/observing.rb, line 187
    def observe(*models)
      models.flatten!
      models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model }
      redefine_method(:observed_classes) { models }
    end

observed_class() click to toggle source

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 208
    def observed_class
      if observed_class_name = name[/(.*)Observer/, 1]
        observed_class_name.constantize
      else
        nil
      end
    end

observed_classes() click to toggle source

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 202
    def observed_classes
      Array.wrap(observed_class)
    end

### Protected Instance Methods

disabled_for?(object) click to toggle source

    # File lib/active_model/observing.rb, line 246
    def disabled_for?(object)
      klass = object.class
      return false unless klass.respond_to?(:observers)
      klass.observers.disabled_for?(self)
    end

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