callbacks.rb

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assignment.rb associations.rb basics.rb callbacks.rb composite.rb conversions.rb database.rb index.rb modifiers.rb queries.rb spec.rb validations.rb

callbacks.rb
¶

Callbacks in [Mongo Model][mongodb_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.

callbacks.rb

Basics

Embedded Models