Book Image

Learning Mongoid

By : Gautam Rege
Book Image

Learning Mongoid

By: Gautam Rege

Overview of this book

Mongoid helps you to leverage the power of schema-less and efficient document-based design, dynamic queries, and atomic modifier operations. Mongoid eases the work of Ruby developers while they are working on complex frameworks. Starting with why and how you should use Mongoid, this book covers the various components of Mongoid. It then delves deeper into the detail of queries and relations, and you will learn some tips and tricks on improving performance. With this book, you will be able to build robust and large-scale web applications with Mongoid and Rails. Starting with the basics, this book introduces you to components such as moped and origin, and how information is managed, learn about the various datatypes, embedded documents, arrays, and hashes. You will learn how a document is stored and manipulated with callbacks, validations, and even atomic updates. This book will then show you the querying mechanism in detail, right from simple to complex queries, and even explains eager loading, lazy evaluation, and chaining of queries. Finally, this book will explain the importance of performance tuning and how to use the right indexes. It also explains MapReduce and the Aggregation Framework.
Table of Contents (14 chapters)
Learning Mongoid
About the Author
About the Reviewers

The belongs_to relation

The belongs_to relation is the child side of the relation. It is set to complement the has_one or has_many relations. This method takes the following options in addition to :autosave, :autobuild, :dependent, :primary_key, and :foreign_key.


The index option determines if the foreign key is indexed or not. It's recommended that foreign keys must be indexed. The values are set to true or false as shown in the following code:

class Book
  include Mongoid::Document

  belongs_to :author, index: true


This is used to complement the :as option for the parent relationship. This option sets the polymorphic resource as follows:

class Vehicle
  include Mongoid::Document

  belongs_to :resource, polymorphic: true


The touch method allows the child object to update the updated_at field of the parent when the child is changed.


When we add or remove a child, we often require the parent object to be updated with a counter. This increment or decrement...