Mongoid Observer using ActiveModel.

mongoid.rb

require "#{RAILS_ROOT}/lib/mongoid/lib/observing.rb"

# Initializer for Observers

User.observers = :user_observer
User.instantiate_observers

# The preferred syntax, similar to AR's setup
# Mongoid.configure do |config|
#   config.observers = :user_observer
# end

observing.rb

module Mongoid
  module Observing
    CALLBACKS = [
      :before_create, :before_destroy, :before_save, :before_update,
      :before_validation, :after_create, :after_destroy, :after_save,
      :after_update, :after_validation
    ]

    def self.included(base)
      base.module_eval { include ActiveModel::Observing }

      CALLBACKS.each do |callback|
        callback_method = :"notify_observers_#{callback}"

        base.module_eval <<-RUBY, __FILE__, __LINE__+1
          #{callback}(#{callback_method.inspect})

          def #{callback_method}(&block)
            notify_observers(#{callback.inspect}, &block)
          end
          private #{callback_method.inspect}
        RUBY
      end
    end
  end
end

user.rb

require 'carrierwave/orm/mongoid'  

class User
  include Mongoid::Document
  include Mongoid::Timestamps
  include Mongoid::Observing
  
  field :name
  field :username
end

user_observer.rb

class UserObserver < ActiveModel::Observer  
  def after_validation(user)
    puts "User Observer After Validation"
  end
end

If you upgrade to Mongoid master then you'll get core support for observers. Add your observers to Mongoid.observers and make them inherit from Mongoid::Observer.

Got it to work with cgriego's tips:

• upgrade mongoid gem to master
• create an initializer or equivalent to load the observers: Mongoid.observers << :user_observer
• generate the observer: rails g observer user
• implement observer class "user_observer" and make it inherit from Mongoid::Observer (the generator will set this up for you)

My observer callbacks were called twice. Before and after the original model validation.

Fixed it by removing the explicit callback in the module eval, which causes the observer callback only to trigger after the orignal model callback.

https://gist.github.com/988791

No luck using the core support for observers officially added in Mongoid by @cgriego?

@angelim, works well with the Mongoid::Observer in master, however our production env isn't upgraded to Mongoid >= 2.0.0 yet.