5.5 Running a Migration

As we've just seen, rails generate model created a database migration
file inside the db/migrate directory. Migrations are Ruby classes that
are designed to make it simple to create and modify database tables.
Rails uses rake commands to run migrations, and it's possible to undo a
migration after it's been applied to your database. Migration filenames
include a timestamp to ensure that they're processed in the order that
they were created.