🚀 Using MongoDB in Ruby on Rails with Mongoid: A Practical Example

July 1, 2025

As developers, we often default to relational databases like PostgreSQL or MySQL when building Rails applications. But what happens when your data is better represented as documents, or you need more flexibility with your schema?

That’s where MongoDB comes in — and with the help of Mongoid , integrating it with Rails is smooth and effective.

In this article, I’ll show you how to set up MongoDB with Rails using Mongoid and create a more real-world example model: a digital library .

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Step 1: Add Mongoid to Your Rails App

In your Gemfile, add:

gem 'mongoid', '~> 7.6'

Then run:

bundle install

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Step 2: Generate the Mongoid Configuration

rails g mongoid:config

This command creates config/mongoid.yml, where you can define your database settings (host, port, database name, etc.).

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Optional: Remove ActiveRecord if not needed

If you plan to use only MongoDB:

In config/application.rb, remove:

require "active_record/railtie"

Then remove or comment out database.yml.

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Step 3: Create a Real-World Document Model – Book

Let’s imagine we’re building a digital library. Here’s a Book model with fields that reflect actual publishing data:

class Book
  include Mongoid::Document
  include Mongoid::Timestamps

  field :title, type: String
  field :author, type: String
  field :genre, type: String
  field :isbn, type: String
  field :language, type: String
  field :published_year, type: Integer
  field :pages, type: Integer
  field :publisher, type: String
  field :description, type: String
  field :available, type: Boolean, default: true
end

Notice how easy it is to add new fields — no need to create migrations or worry about schema changes.

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Step 4: Create and Query Documents

Open Rails console:

rails c

Then create a book:

Book.create(
  title: "Siddhartha",
  author: "Hermann Hesse",
  genre: "Philosophical Fiction",
  isbn: "9780142437186",
  language: "English",
  published_year: 1922,
  pages: 152,
  publisher: "Penguin",
  description: "A spiritual journey of self-discovery",
)

Query books:

Book.where(author: "Hermann Hesse")
Book.where(available: true)
Book.find_by(isbn: "9780142437186")

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Optional: Build a Simple API

Want to expose your data via a RESTful API?

Here’s an example controller:

class BooksController < ApplicationController
  def index
    render json: Book.all
  end

  def show
    render json: Book.find(params[:id])
  end

  def create
    book = Book.new(book_params)
    if book.save
      render json: book, status: :created
    else
      render json: book.errors, status: :unprocessable_entity
    end
  end

  private

  def book_params
    params.require(:book).permit(
      :title, :author, :genre, :isbn, :language,
      :published_year, :pages, :publisher, :description, :available
    )
  end
end

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Why Use MongoDB in Rails?

MongoDB is a great choice when:

• Your data is document-oriented
• The structure can vary across records
• You want to avoid complex joins
• You need faster prototyping

Mongoid makes the integration seamless — giving you a flexible way to work with modern NoSQL databases while enjoying the elegance of Rails.

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Final Thoughts

If your app requires flexibility, rapid iteration, and a schema-less design, consider using MongoDB with Mongoid. It’s a powerful combination for modern Rails development.

Let me know if you’re using MongoDB in your own Rails apps — I’d love to hear how you’re leveraging it!