MongoDB + PostGres + RoR

First steps

Create the rails application:

$ rails new mongo-psql --database=postgresql

Setup rails config.yml for Postgres connection

The config/database.yml will look like this:

default: &default
  adapter: postgresql
  encoding: unicode
  timeout: 5000
  # For details on connection pooling, see Rails configuration guide
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: mongo-psql_development

Create the model mapping for ActiveRecord

Generate resourcers for a User model, using ActiveRecord model:

$ rails g scaffold User name:string email:string

The generated migration file db/migrate/*_create_users.rb will look like:

class CreateUsers < ActiveRecord::Migration[5.2]
  def change
    create_table :users do |t|
      t.string :name
      t.string :email
      t.timestamps
    end
  end
end

Test Postgres connection

Run

$ rails console
> User.create!(name: “Root”, email: “root@test.com”)

Create Mongo connection for Rails application

There are several GEMs to interact with MongoDB. I used the MongoID GEM. Mongoid is a ODM (object document mapper) framework for Mongo in Ruby. You can find more information HERE.

Append to MongoID to your gemfile

gem "mongoid", "~> 7.0.2"

Run the Mongoid configuration installation script:

$ rails g mongoid:config

Which creates the config/mongoid.yml

• Configure Rails model generator when the mongoid gem is installed and its configuration script is executed, mongoid becomes the default database for all generators. If you wish to keep the generator to the SQL database (in this case PostgreSql), add the following to the Application class (config/application.rb):

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

Now, if you want to generate the model with MongoDb then use following command.

$ rails g model Test --orm=Mongoid
OR
$ rails g mongoid:model Phone

Create Mongoid model files

Run

$ rails g model Phone

Change app/model/phone.rb to:

#app/model/phone.rb
class Phone
  include Mongoid::Document
  include Mongoid::Timestamps

  field :user_id, type: Integer
  field :number, type: String
end

MongoDb and PostGreSql relationships

Define how user.rb will use phone:

class User < ActiveRecord::Base

  def phone
    Phone.where(user_id: self.id).order_by({created_at: -1}).one
  end

  def phone=(phone)
    Phone.create!(user_id: self.id, status: status)
  end

  def phones
    Phone.where(user_id: self.id).order_by({created_at: -1})
  end

end

Define how phone.rb will use user:

class Phone
  include Mongoid::Document
  include Mongoid::Timestamps

  field :user_id, type: Integer
  field :number, type: String

  def user
    User.find(self.user_id)
  end
end