create_yolos.rb

class CreateYolos < ActiveRecord::Migration
  def change
    create_table :yolos do |t|
      # The correct way to add a `longtext` field to table
      t.text :swag, :limit => 0xffffffff
      t.timestamps
    end
  end
end

show_create_table.sql

mysql> show create table yolos;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                    |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| yolos | CREATE TABLE `yolos` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `swag` longtext COLLATE utf8_unicode_ci,
  `created_at` datetime NOT NULL,
  `updated_at` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+