DEV Community


How to install and use MongoDB with Rails 6

prsanjay profile image Sanjay Prajapati Originally published at ・5 min read

How to install and use MongoDB with Rails 6

Rails MongoDB : Introduction

MongoDB is a document database with the scalability, flexibility and the querying and indexing of the records.

In this blog, we will cover how to install it in Ubuntu 16.04, configure and use it with Rails 6 application.

1. Install in Ubuntu 16.04 LTS

The steps are for Ubuntu 16.04 but you can install in other versions as well.

Follow below steps in your terminal to install it from the source.

sudo apt-key adv --keyserver hkp:// --recv EA312927

echo "deb xenial/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list

After adding this repo update the packages

sudo apt-get update

Now, install mongo db using below command

sudo apt-get install -y mongodb-org

`If you face any issue like below`

WARNING: The following packages cannot be authenticated!

mongodb-org-shell mongodb-org-server mongodb-org-mongos mongodb-org-tools mongodb-org

E:There were unauthenticated packages and -y was used without --allow-unauthenticated

Then install it using the below command. Please note the risk of overriding the authentication warning here.

sudo apt-get --allow-unauthenticated install -y mongodb-org

2. Configuration and Starting the Services

After you are done with the installation, configure and start the service using below commands in your terminal

sudo systemctl start mongod

Check if the service has properly started or not using below command

sudo systemctl status mongod

Using below command you can start it automatically when your system starts

sudo systemctl enable mongod

Now, MongoDB is set up and services are running. Let’s see how to use it with Rails 6

Read Also: Notable ActiveRecord Changes in Rails 6

3. Setup with Rails 6

Create a new rails application using below command:

rails new mongorails --skip-active-record --skip-bundle

We have used --skip-active-record dependencies as we are not using it. We also used  --skip-bundle to skip gem installations as we need to change the gemfile to add MongoDB dependency.

If you are going to to use RSpec for testing then you can create your application using below command by skipping the default testing framework of rails

rails new mongorails --skip-active-record --skip-bundle --skip-test --skip-system-test

Now, go to your project directory and add mongoid gem in Gemfile. Mongoid is the officially supported ODM (Object-Document-Mapper) framework for MongoDB in Ruby on Rails Development.

gem 'mongoid', '~> 7.0.5'

NOTE:  Mongoid 7.0.5 or higher is required to use Rails 6.0.

Run below command to install the gem

bundle install

Run below command to generate a default configuration

bin/rails g mongoid:config

This command would create a mongoid.yml file in config directory which is a replacement of database.yml which rails create by default for us.

It is recommended to change server_selection_timeout

from 30 seconds to 1 second for the development environment. You can change it in mongoid.yml

Now, start rails server to check if everything is set up and configured correctly

rails s

If you see below screen after visiting localhost:3000  in your browser then everything is good so far.

rails6 mongodb

4. How to use with Rails

Now, let's create scaffolds using rails and check how the Model is working with MongoDB.

We will create a small application where people can create posts and can comment on it.

Creating Posts

Create a post using scaffolding. Yes, you can use scaffolding with MongoDB as well, and it would create all necessary files as it does for other databases.

rails generate scaffold Post title:string body:text

The important point to note is that we do not have a db folder and there is no need to run migrations.

Post model will look like this

post model in mongodb ruby on rails

Now, head to the browser and visit localhost:3000/posts and you will see a list of posts and you can create/update/delete the posts. Same old rails stuff :)

Once you create the post it will fire insert query as below:

rails mongodb integration - insert query

You can notice that it has first found the database name mongorails_development.insert and then used the below syntax to insert the record to the posts table.

{"insert"=>"posts", "documents"=>[{"_id"=>BSON::ObjectId('5e7d91f2d3527338a88a0751'), "title"=>"Shiny Post", "body"=>"Lorem ipsum"}], "ordered"=>true}

And when you visit show path of the app, it would fire below query

mongorails_development.find | STARTED | {"find"=>"posts", "filter"=>{"_id"=>BSON::ObjectId('5e7d91f2d3527338a88a0751')}}

You can find the post from your rails console using below command


Creating a comment

Let’s create comments on the blogs

Run below command to create comment and associate with posts using scaffold

rails generate scaffold Comment name:string message:string post:belongs_to

By default, it would generate comment model code as below.

ruby on rails with mongodb

Change embedded_in :post to belongs_to :post

Open comments/_form and change the type of field for :message from text_field to text_area, as well as the type of field for :post_id from text_field to hidden_field

Add below code in posts/show.html.erb to create comments for the post. This will list all the comments for the post and also allow you to add new comments.

ruby on rails mongodb

Now, create _comment.html.erb partial in app/views/comments folder with the code below:

mongodb rails

If you want to add a new field to the table just add it using the below line. I have added a new field to posts table using below line

field :slug, type: String

It is that simple!!

You don’t need to declare a foreign key field to comment on the model. It would implicitly create the post_id to comments table. The naming convention for a foreign key is the same as active records.

That's it, You have created a small application using MongoDB.

Discussion (1)

megatux profile image
Cristian Molina

Is it possible to use active_storage with MongoId? I'm unable to setup it

Forem Open with the Forem app