Class: Neo4j::Rails::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. Neo4j's observers work similar to ActiveRecord's. Example:

class CommentObserver < Neo4j::Rails::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 < Neo4j::Rails::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 < Neo4j::Rails::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 < Neo4j::Rails::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.

Available callback methods

• 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

Storing Observers in Rails

If you're using Neo4j within Rails, observer classes are usually stored in app/models with the naming convention of app/models/audit_observer.rb.

Configuration

In order to activate an observer, list it in the config.neo4j.observers configuration setting in your config/application.rb file.

config.neo4j.observers = [:comment_observer, :signup_observer]

Observers will not be invoked unless you define them in your application configuration.

During testing you may want (and probably should) to disable all the observers. Most of the time you don't want any kind of emails to be sent when creating objects. This should improve the speed of your tests and isolate the models and observer logic.

For example, the following will disable the observers in RSpec:

config.before(:each) { Neo4j::Rails::Observer.disable_observers }

But if you do want to run a particular observer(s) as part of the test, you can temporarily enable it:

Neo4j::Rails::Observer.with_observers(:user_recorder, :account_observer) do
  # Any code here will work with observers enabled
end

Loading

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.