Auto Observer – implement Callback and Observing interfaces for Rails

The purpose of this project it to examine how callbacks and observers can be created in a convenient re-usable form.

• Add Callbacks with Observing for certain operations

  require 'auto-observer'
  
  class Client
    include AutoObserver
  
    attr_accessor :before_visit, :after_visit
  
    auto_observer_callbacks :tickle, :only => [:after, :before]
  
    def tickle
      "giggle"
    end
  
    before_tickle :pre_tickle_processing
    after_tickle :post_tickle_processing
  
    def before_visit
      @before_visit ||= [ ]
    end
  
    def after_visit
      @after_visit ||= [ ]
    end
  
    def pre_tickle_processing
      before_visit << :pre_tickle_processing
    end
  
    def post_tickle_processing
      after_visit << :post_tickle_processing
    end
    include AutoObserver::AliasMethodBind
  end
  

This generates before_tickle, and after_tickle class methods that wrap your tickle instance method by wrapping define_model_callback with auto_observer_callbacks class helper.

This also initializes Client with observing functionality, hooking up notifications to observer classes that are registered with this Class.

The include AutoObserver::AliasMethodBind alias_method_chains each of the callback methods.

• Observer registration

  class ClientObserver < ActiveModel::Observer
    def before_tickle(client)
      client.before_visit << :before_tickle
    end
  end
  
  class AnotherClientObserver < ActiveModel::Observer
    observe :client
  
    def before_tickle(client)
      client.before_visit << :before_another_tickle
    end
  
    def after_tickle(client)
      client.after_visit << :after_another_tickle
    end
  end
  

• Register with Client and initialize

  Client.observers = :client_observer, :another_client_observer
  Client.instantiate_observers
  

• In use

  client = Client.new
  client.before_visit == []   #=> true
  client.after_visit == []    #=> true
  
  client.tickle    #=> "giggle"
  
  client.before_visit == [ 
    :before_tickle, :before_another_tickle, :pre_tickle_processing
  ]    #=> true
  client.after_visit == [ 
    :post_tickle_processing, :after_another_tickle
  ]    #=> true