Sequel + uuid-ossp

1_create_products.rb

Sequel.migration do
  up do
    run 'CREATE EXTENSION "uuid-ossp"'

    create_table :products do
      column :id, :uuid, :default => Sequel.function(:uuid_generate_v4), :primary_key => true
    end
  end
end

Please note that CREATE EXTENSION is only available to superuser in postgres. I do not think it is a good practice to run app migrations using superuser.