active_record.rb

Rails Active record

create new project 
$rails new active_record

create model
$rails g model Manufacturer name:string

generate the game model
$rails g model Game name:string  manufacturer:references

$bundle exec rake db:migrate

$sqlite3 db/development.sqlite3

> .tables

> .schema manufacturers 

> .schema games


$ rails console --sandbox
Loading development environment in sandbox (Rails 4.2.5)
Any modifications you make will be rolled back on exit

2.2.1 :001 > manufacturer = Manufacturer.create(name:'Sega')

 => #<Manufacturer id: 1, name: "Sega", created_at: "2015-12-15 05:14:52", updated_at: "2015-12-15 05:14:52"> 

2.2.1 :002 > game = Game.create(name: 'shinobi', manufacturer: manufacturer) //it knows that manufacturer key means the manufacturer_id

 => #<Game id: 1, name: "shinobi", manufacturer_id: 1, created_at: "2015-12-15 05:29:55", updated_at: "2015-12-15 05:29:55"> 

2.2.1 :003 > game.manufacturer_id

 => 1 

2.2.1 :004 > game.manufacturer.name

 => "Sega"