Helper module for denormalizing association attributes in Mongoid models.
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README.md

Mongoid::Denormalize

Helper module for denormalizing association attributes in Mongoid models. Why denormalize? Read A Note on Denormalization.

Extracted from coookin', where it is used in production.

Installation

Add the gem to your Bundler Gemfile:

gem 'mongoid_denormalize'

Or install with RubyGems:

$ gem install mongoid_denormalize

Usage

In your model:

# Include the helper method
include Mongoid::Denormalize

# Define your denormalized fields
denormalize :name, :email, :from => :user

Example

class User
  include Mongoid::Document
  include Mongoid::Denormalize

  has_many :comments

  field :name
  field :email
  
  denormalize :name, :email, :to => :comments
end

class Comment
  include Mongoid::Document
  include Mongoid::Denormalize

  belongs_to :user

  field :body
  
  denormalize :name, :email, :from => :user
end

>> user = User.create(:name => "John Doe", :email => "john@doe.com")
>> comment = Comment.create(:body => "Lorem ipsum...", :user => user)
>> user.comments << comment
>> comment.user_name
"John Doe"
>> comment.user_email
"john@doe.com"
>> user.update_attributes(:name => "Bill")
>> comment.user_name
"Bill"

Options

Denormalization can happen in either or both directions. When using the :from option, the associated objects will fetch the values from the parent. When using the :to option, the parent will push the values to its children.

# Basic denormalization. Will set the user_name attribute with the associated user's name.
denormalize :name, :from => :user

# Basic denormalization. Will set the user_name attribute of "self.comments" with "self.name".
denormalize :name, :to => :comments

# Multiple fields. Will set the user_name and user_email attributes with the associated user's name and email.
denormalize :name, :email, :from => :user

# Multiple children. Will set the user_name attribute of "self.posts" and "self.comments" with "self.name".
denormalize :name, :to => [:posts, :comments]

You must specify the type of all denormalizations when using the :from option, unless the denormalized type is String, the default.

# in User
field :location, :type => Array
denormalize :location, :to => :posts

# in Post
denormalize :location, :type => Array, :from => :user

Rake tasks

A rake task is included for verifying and repairing inconsistent denormalizations. This might be useful your records may be modified without Mongoid, or if you are using relational associations in combination with embedded records (see Known issues).

rake db:denormalize

This task will only update records that have outdated denormalized fields.

Known issues

Relational associations in combination with embedded records

It is not recommended nor supported to use mongoid_denormalize to perform denormalization to embedded records through a relational association because MongoDB/Mongoid do not support direct access to embedded fields via a relational association.

So, if User has_many :posts and User has_many :comments, but Comments are embedded_in :post, a user can't directly access a comment.

Contributors

Credits

Copyright (c) 2010 Logan Raarup, released under the MIT license.