Callbacks

Mongoid implements many of the ActiveRecord callbacks.

Document Callbacks

Mongoid supports the following callbacks for documents </tutorials/documents>:

• after_initialize
• after_build
• before_validation
• after_validation
• before_create
• around_create
• after_create
• after_find
• before_update
• around_update
• after_update
• before_upsert
• around_upsert
• after_upsert
• before_save
• around_save
• after_save
• before_destroy
• around_destroy
• after_destroy

Callbacks are available on any document, whether it is embedded within another document or not. Note that to be efficient, Mongoid only invokes the callback on the document that the persistence action was executed on. This enables Mongoid to support large hierarchies and to handle optimized atomic updates efficiently (without invoking callbacks throughout the document hierarchy).

Note that using callbacks for domain logic is a bad design practice, and can lead to unexpected errors that are hard to debug when callbacks in the chain halt execution. It is our recommendation to only use them for cross-cutting concerns, like queueing up background jobs.

class Article
  include Mongoid::Document
  field :name, type: String
  field :body, type: String
  field :slug, type: String

  before_create :send_message

  after_save do |document|
    # Handle callback here.
  end

  protected
  def send_message
    # Message sending code here.
  end
end

Callbacks are coming from Active Support, so you can use the new syntax as well:

class Article
  include Mongoid::Document
  field :name, type: String

  set_callback(:create, :before) do |document|
    # Message sending code here.
  end
end

Association Callbacks

Mongoid has a set of callbacks that are specific to associations - these are:

• after_add
• after_remove
• before_add
• before_remove

Each time a document is added or removed from any of the following associations, the respective callbacks are invoked: embeds_many, has_many and has_and_belongs_to_many.

Association callbacks are specified as options on the respective association. The document added/removed will be passed as the parameter to the specified callback. Example:

class Person
  include Mongoid::Document

  has_many :posts, after_add: :send_email_to_subscribers
end

def send_email_to_subscribers(post)
  Notifications.new_post(post).deliver
end