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

Atomic modifiers

Atomic modifiers are those that modify the fields in an atomic operation. We saw an example of this in the earlier chapter with :counter_cache, which atomically increments or decrements the value of a field.

While it's easy to manipulate fields in a document, how about if we want to atomically find or modify documents? In SQL, we have INSERT ON DUPLICATE KEY UPDATE and this is called an upsert. Similarly, MongoDB also supports upserts. We have already seen methods, such as :find_and_create and :find_and_initialize. Now, we will see :find_and_modify.


As the name suggests, we find and modify in a single atomic operation. This is useful in various scenarios where we want to compare and set in a single operation. For example, a Job queue, where a worker processes is supposed to pick up a job and execute them. It's important that only one worker picks up a job. Suppose we have a job class as follows:

class Job
  include Mongoid::Document

  field :name
  field :status...