app.rb

require 'active_record'

require_relative('./make')
require_relative('./car')


class App 

    	def run
	    ActiveRecord::Base.establish_connection(
	      adapter: :postgresql,
	      database: 'dealership'
	    )
	    
	    bmw = Make.create(company_name: "BMW", established_at: 1916)
	    p bmw
	
	    three_series = Car.create(stock: 20, model: "3 Series", make: bmw)
	    four_series = Car.create(stock: 3, model: "4 Series", make: bmw)
	    five_series = Car.create(stock: 1, model: "M5", make_id: bmw.id)
	    
	    # Car.where({make_id: bmw.id})
	
	    bmw.cars.each do |current_car|
	    p current_car
	    
	    end
	
	    # Make.find({id: five_series.make_id})
	
	    p five_series.make
	end
	
end

App.new.run

car.rb

class Car < ActiveRecord::Base

	belongs_to :make

end

Gemfile

gem 'activerecord'
gem 'pg'

make.rb

class Make < ActiveRecord::Base

	has_many :cars

end