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

Embedded documents

As the name suggests, documents embedded inside other documents are called embedded documents. When the parent document is fetched, it also fetches all the embedded documents. This is similar to the composition concept.

The following code shows how we can define an embedded document:

class Address
  include Mongoid::Document

  field :street, type: String
  field :city, type: String
  field :state, type: String
  field :zipcode, type: String
  field :country, type: String

  embedded_in :author

And the following code denotes how we can embed it into another model:

class Author
  include Mongoid::Document

  field :name, type: String
  has_many :books
  embeds_one :address

Now let's have a quick look at how this information was stored in the database. As it was an embedded document, when we fetched the author object, we also got the author's address.

> db.authors.findOne()
  "_id" : ObjectId("5143678345db7ca255000001"),
  "address" : {
    "_id" : ObjectId("514367f445db7ca255000003...