Installation in Rails

Using MongoMapper with Rails 3 and 4 is easier than ever. Thanks to new features in ActiveSupport, and the new ActiveModel framework (which MongoMapper 0.9+ uses), your app can be up and running on MongoDB in a matter of seconds.

First, if you’re generating a new Rails application, it is recommended to leave out the ActiveRecord dependencies (unless you need them of course). From the console, just run:

rails new my_app --skip-active-record

But, not everyone is starting fresh. Andy Lindeman has an eBook about upgrading from Rails 3 to Rails 4. If you’re not upgrading, but just converting an existing Rails application from ActiveRecord (or another ORM), simply open config/application.rb and replace:

require 'rails/all'

With (for Rails 3):

# Pick the frameworks you want:
require "action_controller/railtie"
require "action_mailer/railtie"
require "active_resource/railtie"
require "sprockets/railtie"
require "rails/test_unit/railtie"

Or (for Rails 4):

# Pick the frameworks you want:
require "action_controller/railtie"
require "action_mailer/railtie"
require "active_model/railtie"
require "action_view/railtie"
require "sprockets/railtie"
require "rails/test_unit/railtie"

Next, add MongoMapper to your Gemfile, and run bundle install:

gem 'mongo_mapper'
gem 'bson_ext'

Now, you’re almost ready to go, but you still need some configuration info. Generate config/mongo.yml by running:

bundle exec rails generate mongo_mapper:config

If you want to configure your application with a MongoDB URI (i.e. on Heroku), then you can use the following settings for your production environment:

production:
 uri: <%= ENV['MONGODB_URI'] %>

Technically, you can initialize MongoMapper and use it to store data now. However, I like to configure Rails’ model generator. Inside of the Application class (config/application.rb) I add:

config.generators do |g|
  g.orm :mongo_mapper
end

One other small note, make sure any ActiveRecord related configuration items are commented out or removed like below:

# config.active_record.whitelist_attributes = true

This will allow you to use the rails generate model command with MongoMapper.

You’re now finished, go forth and create!

Generate a user model with bundle exec rails g model user name:string:

      invoke  mongo_mapper
      create    app/models/user.rb
      invoke    test_unit
      create      test/models/user_test.rb
      create      test/fixtures/users.yml

Create a user with bundle exec rails c:

Loading development environment (Rails 4.1.1)
irb(main):001:0> user = User.new(name: 'Mongo')
=> #<User _id: BSON::ObjectId('539645eb43ebd927b2000001'), name: "Mongo">
irb(main):002:0> user.valid?
=> true
irb(main):003:0> user.save
=> true
irb(main):004:0> User.all.count
=> 1