composite.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

composite.rb
¶

Example of Composite Objects using [Mongo Model][mongodb_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][callbacks], [validations][validations] and [conversions][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.