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composite.rb

Example of Composite Objects using Mongo Model.

Models are just ordinary Ruby Objects, so You can combine and mix it as You wish. The only differences are

  • main object has the _id attribute.
  • child objects doesn’t have _id, but have _parent – reference to the main object.

Callbacks, validations and conversions works on embedded objects the same way as on the main.

In this example we’ll create simple Blog Application and see how to embed Comments into the Post.

 
require 'mongo/model'

Connecting to test database and cleaning it before starting.

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

Defining Post.

 
class Post
  inherit Mongo::Model
  collection :posts

  attr_accessor :text

We using plain Ruby Array as container for Comments.

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

Defining Comment.

 
class Comment
  inherit Mongo::Model

  attr_accessor :text

We need a way to access Post from Comment, every child object has _parent reference, let’s use it.

 
  alias_method :post, :_parent
end

Creating Post with Comments and saving it to database.

 
post = Post.new text: 'Zerg infestation found on Tarsonis!'
post.comments << Comment.new(text: "I can't believe it.")
post.save

Retrieving from database.

 
post = Post.first
p post.comments.class                         # => Array
p post.comments.size                          # => 1
p post.comments.first.text                    # => "I can't believe it"
p post.comments.first.post == post            # => true

Adding another comment.

 
post.comments << Comment.new(text: "Me too, but it's true.")
post.save

Reading updated post.

 
post = Post.first
p post.comments.size                           # => 2

In this example we covered how to create and use composite objects (embedded objects) – use plain Ruby Objects and the Driver will figure out how to save and restore it.