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Getting Started (Sinatra)

On this page

  • New Application
  • Create Git Repo
  • Create Gemfile
  • Install Dependencies
  • Run MongoDB Locally
  • Use MongoDB Atlas
  • Basic Application
  • Run Application
  • Existing Application

This section shows how to create a new Sinatra application using Mongoid for data access. The process is similar for other Ruby applications not using Ruby on Rails.

The complete source code for this application is available in the mongoid-demo GitHub repository.

While not required, we recommend creating a Git repository for your application:

git init blog
cd blog

Commit your changes as you are following this tutorial.

Create a file named Gemfile with the following contents:

source ''
gem 'sinatra'
gem 'mongoid'
gem 'puma'

Run the following commands to install the dependencies:

gem install bundler
bundle install

This command will generate a file named Gemfile.lock which we recommend committing to your Git repository.

To develop locally with MongoDB, download and install MongoDB.

Once MongoDB is installed and running, create a file named config/mongoid.yml pointing to your deployment. For example, if you launched a standalone mongod on the default port, the following contents would be appropriate:

database: blog_development
- localhost:27017
server_selection_timeout: 1

Instead of downloading, installing and running MongoDB locally, you can create a free MongoDB Atlas account and create a free MongoDB cluster in Atlas. Once the cluster is created, follow the instructions in connect to the cluster page to obtain the URI. Use the Ruby driver 2.5 or later format.

Create a file named config/mongoid.yml with the following contents, replacing the URI with the actual URI for your cluster:

uri: mongodb+srv://
server_selection_timeout: 5

Create a file named app.rb with the following contents. First, some requires:

require 'sinatra'
require 'mongoid'

Load the Mongoid configuration file and configure Mongoid. This is done automatically when Mongoid is used with Rails, but since we are using Mongoid with Sinatra, we need to do this ourselves:

Mongoid.load!(File.join(File.dirname(__FILE__), 'config', 'mongoid.yml'))

Now we can define some models:

class Post
include Mongoid::Document
field :title, type: String
field :body, type: String
has_many :comments
class Comment
include Mongoid::Document
field :name, type: String
field :message, type: String
belongs_to :post

... and add some routes:

get '/posts' do
post '/posts' do
post = Post.create!(params[:post])
get '/posts/:post_id' do |post_id|
post = Post.find(post_id)
comments: post.comments,
post '/posts/:post_id/comments' do |post_id|
post = Post.find(post_id)
comment = post.comments.create!(params[:comment])

Launch the application:

bundle exec ruby app.rb

Try some requests via curl:

curl http://localhost:4567/posts
# => []
curl -d 'post[title]=hello&post[body]=hello+world' http://localhost:4567/posts
# => {"_id":{"$oid":"5d8151ec96fb4f0ed5a7a03f"},"body":"hello world","title":"hello"}
curl http://localhost:4567/posts
# => [{"_id":{"_id":{"$oid":"5d8151ec96fb4f0ed5a7a03f"},"body":"hello world","title":"hello"}]
curl -d 'comment[name]=David&comment[message]=I+like' http://localhost:4567/posts/5d8151ec96fb4f0ed5a7a03f/comments
# => {}
curl http://localhost:4567/posts/5d8151ec96fb4f0ed5a7a03f
# => {"_id":{"$oid":"5d8151ec96fb4f0ed5a7a03f"},"title":"hello","body":"hello world","comments":[{"_id":{"$oid":"5d8157ac96fb4f20c5e45c4d"},"message":"I like","name":"David","post_id":{"$oid":"5d8151ec96fb4f0ed5a7a03f"}}]}

To start using Mongoid in an existing Sinatra applications, the steps are essentially the same as the one given above for a new application:

  1. Add the mongoid dependency to the Gemfile.

  2. Create a mongoid.yml configuration file.

  3. Load the configuration file and configure Mongoid in the application.

  4. Define Mongoid models.

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