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


This section is relevant only if you are using Mongoid 3. IdentityMap has been removed in Mongoid 4 because it now includes Mongoid::Relations::Eager.

An IdentityMap pattern is a design pattern where the object gets loaded only once from the database, and is then stored in the map. So, the next lookup is directly from the map and hence faster. The IdentityMap pattern has been implemented in Mongoid (and removed in the latest version).


Ignore the rest of this section if you use Mongoid4. Only if you are using Mongoid 3, is the remaining section relevant.

If enabled properly, IdentityMap can greatly improve the performance of queries. Whenever a document is loaded from the database, it is classified by class and ID kept in the IdentityMap pattern. Then, when that document is looked up the next time, Mongoid looks into the IdentityMap pattern before looking into the database.

So, how do we know that the IdentityMap pattern is there? First, enable it.

# config/mongoid.yml