Add a new observer to the pool. The new observer needs to respond to update, otherwise it raises an ArgumentError exception.

  class Foo
    include ActiveModel::Observing
  end

  class FooObserver < ActiveModel::Observer
  end

  Foo.add_observer(FooObserver.instance)

  Foo.observers_instance
  # => [#<FooObserver:0x007fccf55d9390>]

count_observers is deprecated. Use observers_count.

Instantiate the global observers.

  class Foo
    include ActiveModel::Observing

    attr_accessor :status
  end

  class FooObserver < ActiveModel::Observer
    def on_spec(record, *args)
      record.status = true
    end
  end

  Foo.observers = FooObserver

  foo = Foo.new
  foo.status = false
  foo.notify_observers(:on_spec)
  foo.status # => false

  Foo.instantiate_observers # => [FooObserver]

  foo = Foo.new
  foo.status = false
  foo.notify_observers(:on_spec)
  foo.status # => true

Fires notifications to model‘s observers.

  def save
    notify_observers(:before_save)
    ...
    notify_observers(:after_save)
  end

Custom notifications can be sent in a similar fashion:

  notify_observers(:custom_notification, :foo)

This will call custom_notification, passing as arguments the current object and :foo.

Returns the current observer instances.

  class Foo
    include ActiveModel::Observing

    attr_accessor :status
  end

  class FooObserver < ActiveModel::Observer
    def on_spec(record, *args)
      record.status = true
    end
  end

  Foo.observers = FooObserver
  Foo.instantiate_observers

  Foo.observer_instances # => [#<FooObserver:0x007fc212c40820>]

Gets an array of observers observing this model. The array also provides enable and disable methods that allow you to selectively enable and disable observers (see ActiveModel::ObserverArray.enable and ActiveModel::ObserverArray.disable for more on this).

  class ORM
    include ActiveModel::Observing
  end

  ORM.observers = :cacher, :garbage_collector
  ORM.observers       # => [:cacher, :garbage_collector]
  ORM.observers.class # => ActiveModel::ObserverArray

Activates the observers assigned.

  class ORM
    include ActiveModel::Observing
  end

  # Calls PersonObserver.instance
  ORM.observers = :person_observer

  # Calls Cacher.instance and GarbageCollector.instance
  ORM.observers = :cacher, :garbage_collector

  # Same as above, just using explicit class references
  ORM.observers = Cacher, GarbageCollector

Note: Setting this does not instantiate the observers yet. instantiate_observers is called during startup, and before each development request.

Returns the total number of instantiated observers.

  class Foo
    include ActiveModel::Observing

    attr_accessor :status
  end

  class FooObserver < ActiveModel::Observer
    def on_spec(record, *args)
      record.status = true
    end
  end

  Foo.observers = FooObserver
  Foo.observers_count # => 0
  Foo.instantiate_observers
  Foo.observers_count # => 1