Rails 4 has native support for the type UUID (Universally Unique Identifier) in Postgres. In this Div Bit I will describe how you can use it for generating UUIDs without doing it manually in your Rails code.

First you need to enable the Postgres extension ‘uuid-ossp’:

class CreateUuidPsqlExtension < ActiveRecord::Migration
  def self.up
    execute "CREATE EXTENSION \"uuid-ossp\";"
  end

  def self.down
    execute "DROP EXTENSION \"uuid-ossp\";"
  end
end

You can use a UUID as a ID replacement:

create_table :translations, id: :uuid do |t|
  t.string :title
  t.timestamps
end

In this case the Translations table will have a UUID as ID and it is autogenerated. The uuid-ossp extension in Postgresq has different algorithms how the UUID is generated. Rails 4 uses v4 per default. You can read more about these algorithms here: http://www.postgresql.org/docs/current/static/uuid-ossp.html

However, sometimes you don't want to have the UUID as ID replacement and instead have it in a separate column:

class AddUuidToModelsThatNeedIt < ActiveRecord::Migration
  def up
    add_column :translations, :uuid, :uuid
  end

  def down
    remove_column :invoices, :uuid
  end
end

This will create a UUID column, but the UUID will not be autogenerated. You have to do it yourself in Rails with SecureRandom. However, we think that this is a typical database responsibility. Fortunately, the default option in add_column helps:

class AddUuidToModelsThatNeedIt < ActiveRecord::Migration
  def up
    add_column :translations, :uuid, :uuid, :default => "uuid_generate_v4()"
  end

  def down
    remove_column :invoices, :uuid
  end
end

Now the UUID will be created automatically, also for existing records!