Active Record Migrations — Ruby on Rails Guides

Migrations are a feature of Active Record that allows you to evolve your database schema over time. Rather than write schema modifications in pure SQL, migrations allow you to use a Ruby Domain Specific Language (DSL) to describe changes to your tables.After reading this guide, you will know: Which generators you can use to create migrations. Which methods Active Record provides to manipulate your database. How to change existing migrations and update your schema. How migrations relate to schema.rb. How to maintain referential integrity.