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

has_many – the many-to-one relation

The Many-to-One relation is among the most commonly used relations between documents. This is easiest seen in our previous example of authors, and how they are related to their books.

# app/models/author.rb

class Author
  include Mongoid::Document

   has_many :books

# app/models/book.rb

class Book
  include Mongoid::Document

  belongs_to :author

Though it seems very simple at first, let's look a few nuances that are commonly misunderstood.

Notice the model filename is always singular (author.rb, book.rb) as is the name of the model—Author and Book.

Remember, has_many is a method that creates an instance method called books when the Author class is loaded. Similarly, belongs_to is a method that creates an instance method called author when the Book class is loaded.

The relation names are used to infer the model name. So, using the symbols :books and :author, ActiveSupport inflector methods can find out the model names Book and Author respectively...