# Use uuid on rails with PostgreSQL

This guide is a sort of extract of official rails guide: [Official rails guide](http://edgeguides.rubyonrails.org/active_record_postgresql.html)

Here I describe an implementation of **uuid** with **PostgreSQL** >= **9.4**. This requires to enable `pgcrypto`

Example with a creation of a table named trackers:

```rb
class CreateTrackers < ActiveRecord::Migration[5.0]
  def change
    enable_extension 'pgcrypto' unless extension_enabled?('pgcrypto')
    create_table :trackers, id: :uuid, default: 'gen_random_uuid()' do |t|
      t.integer :duration, null: false
      t.string  :description, null: false

      t.timestamps
    end
  end
end
```

You can use **uuid** to define a relation reference

```rb
class CreateProjects < ActiveRecord::Migration[5.0]
  def change
    enable_extension 'pgcrypto' unless extension_enabled?('pgcrypto')
    create_table :projects, id: :uuid, default: 'gen_random_uuid()' do |t|
      t.string :name
      t.uuid :user_id
      t.timestamps
    end
  end
end
```