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


Callbacks are pretty interesting in Mongoid. Just as validations, Mongoid leverages ActiveModel::Callbacks. Callbacks are methods that are called along with persistence. This helps us manipulate the data. We can implement various callbacks such as before_save, after_create, and before_destroy. The entire list of callbacks is available at


Did you know ActiveModel::Callbacks include after_initialize, after_find, after_touch, after_commit, and after_rollback? Of course, after_commit and after_rollback are specific to transactional databases unlike MongoDB.

Mongoid also supports before_upsert, after_upsert, and around_upsert! As we have seen earlier, an upsert means "update if the document exists and create if it doesn't exist". However, there's more to callbacks in Mongoid.

Mongoid also supports the after_add, after_remove, before_add, and before_remove callback for some specific relations. Let's dive deeper into this...