Rails migration to add countries table and populate it with countries gem

rails_migration_create_countries.rb

require 'countries/iso3166'

class CreateCountries < ActiveRecord::Migration[6.0]
  def change
    create_table :countries do |t|
      t.string :name, limit: 64
      t.string :name_it, limit: 64
      t.integer :region, limit: 1
      t.string :iso2, limit: 2
      t.string :phone_prefix, limit: 3
      t.string :currency_code, limit: 5
      t.boolean :eu_member, default: false
      t.string :official_languages, array: true, default: []

      t.timestamps
    end

    reversible do |dir|
      dir.up do
        %w(Europe Americas Asia Africa Oceania).each do |region|
          h_countries = []
          ISO3166::Country.find_all_countries_by_region(region).each do |c|
            h_countries << {name: c.name,
                            name_it: c.translations['it'],
                            region: region.downcase,
                            phone_prefix: c.country_code,
                            iso2: c.alpha2,
                            currency_code: c.currency_code,
                            official_languages: c.languages_official,
                            eu_member: c.data['eu_member'] }
          end
          Country.create(h_countries)
          puts "Create #{h_countries.size} #{Country.model_name.human(count: h_countries.size)} regione #{region}"
        end
      end
    end
  end
end

Add the gem countries to your gemfile without require, since it is only used to populate the table

# Countries is a collection of all sorts of useful information for every country in the ISO 3166 standard
gem 'countries', '~> 3.0.1', require: false

To create the rails model:
bin/rails g model Country name:string{64} name_it:string{64} region:integer{1} iso2:string{2} phone_prefix:string{3} currency_code:string{5}

Add the enum in the rails model:

class Country < ApplicationRecord
  enum region: {europe: 1, americas: 2,  asia: 3,  africa: 4, oceania: 5}
  # ...
end

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