Back in Chapter 2, Schema Design and Data Modeling, we described how to install, connect, and set up models, including an inheritance to Mongoid. Here, we will go through the most common use cases of CRUD.

Finding documents is done using a DSL similar to Active Record (AR). As with AR using a relational database, Mongoid assigns a class to a MongoDB collection (table) and any object instance to a document (row from a relational database):

Book.find('592149c4aabac953a3a1e31e')

This will find the document by ObjectId and return the document with isbn 101, as will the query by a name attribute:

Book.where(name: 'Mastering MongoDB')

In a similar fashion to the dynamically generated AR queries by an attribute, we can use the helper method:

Book.find_by(name: 'Mastering MongoDB')

This queries by attribute name, equivalent to the previous query.

We should enable QueryCache to avoid hitting the database for the same query multiple times, as follows:

Mongoid::QueryCache.enabled = true

This can be added in any code block that we want to enable, or in the initializer for Mongoid.