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callbacks.rb

Callbacks in Mongo Model.

Callbacks are handy way to execute custom logic at special moments of the lifecycle of the model. There are following callbacks available:

before_validate
after_validate

before_save
after_save

before_create
after_create

before_update
after_update

before_delete
after_delete

after_build

All these callbacks also available on embedded models.

In this example we create post with embedded comments and generate teasers on it using callbacks.

 
require 'mongo/model'

Connecting to test database and cleaning it before starting.

 
Mongo::Model.default_database_name = :default_test
Mongo::Model.default_database.clear

Basics

 

      		
    

    

      
        

          
        

        
Defining post, its teaser will be generated before saving.

      		
      
        
class Post
  inherit Mongo::Model
  collection :posts

  attr_accessor :text, :teaser

  protected

      		
    

    

      
        

          
        

        
Using before_save callback to generate teaser before saving the post
(You can also use block version instead of method).

      		
      
        
    def generate_teaser
      @teaser = text[0..4] if text
    end
    before_save :generate_teaser
end

      		
    

    

      
        

          
        

        
Creating post, teaser will be generated when we save the post.

      		
      
        
post = Post.new text: 'Norad II crashed!'
post.save!
p post.teaser                                     # => Norad

      		
    

    

      
        

          
        

        
Embedded Models



Callbacks on children works the same way whith the only difference –
when child removed from main object – child get :delete and main object
:update callbacks, details:



    

  • when main object created/updated/deleted – the same callbacks propagated to
its children.
    • 

  • when child added to existing main object – the main object and all its existing
children get :update callback, but all newly created children get :create callback.
    • 

  • when child removed from existing main object – the main object and all its existing
children get :update callback, but all removed children get :delete callback.
    • 




Let’s add embedded comments to post and see how this works.

      		
      
        

      		
    

    

      
        

          
        

        
Adding comments to post.

      		
      
        
class Post
  def comments; @comments ||= [] end
end

      		
    

    

      
        

          
        

        
Defining comment, his teaser also generated with before_save callback.

      		
      
        
class Comment
  inherit Mongo::Model

  attr_accessor :text, :teaser

  protected
    def generate_teaser
      @teaser = text[0..4] if text
    end
    before_save :generate_teaser
end

      		
    

    

      
        

          
        

        
Creating post.

      		
      
        
post = Post.new text: 'Norad II crashed!'

      		
    

    

      
        

          
        

        
Adding comment to post.

      		
      
        
comment = Comment.new text: 'Where?'
post.comments << comment

      		
    

    

      
        

          
        

        
Saving post, embedded comment also generates its teaser.

      		
      
        
post.save!
p comment.teaser                                  # => 'Where'

      		
    

    

      
        

          
        

        
In this example we examined callbacks, it’s types and how they works on
main and embedded models.