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

Polymorphic relations

Polymorphic means multiple forms or multiple behaviors. For example, a vehicle could mean a two-wheeler, three-wheeler, a car, a truck, or even a space shuttle! So, how do we map these different types of vehicles that have entirely different data but have a relatively common functionality? Enter polymorphic relations! Let's create vehicles using basic polymorphism.

Let's design the Vehicle model:

# app/models/vehicle.rb

class Vehicle
  include Mongoid::Document

  belongs_to :resource, polymorphic: true

  field :terrain, type: String
  field :cost, type: Float
  field :weight, type: Float
  field :max_speed, type: Float

This is the main polymorphic class. We now use this class in other models. Now, each model we build is independent and can choose to be related to Vehicle. It has its own identity and does not inherit from any parent model, but it will be treated like a vehicle.

Let's create a Bike class:

# app/models/bike.rb
class Bike
  include Mongoid::Document