ActiveRecord::Migration outside of Rails

migration.rb

DB_FILE = 'tmp/test_db'

FileUtils.mkdir_p File.dirname(DB_FILE)
FileUtils.rm_f DB_FILE

ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: DB_FILE

ActiveRecord::Migration.class_exec do
  self.verbose = false
  
  create_table :users do |t|
    t.string :username
    t.index  :username, unique: true
    t.string :email
    t.index  :email, unique: true
  end
  
  create_table :articles do |t|
    t.string :title
    t.text :content
    t.references :user
  end
end