What are migrations in Rails?

[Hussein Baghdadi]

Hey,
In Rails applications, what are "Database Migrations"?
Thanks.

[Gregg Bolinger]

Um, they are database migrations. It is what is sounds like It's a means to migrate changes in your domain/model structure to the database schema.

[David Newton]

Searching the web would probably be the easiest way to find further information.

But yes: they're programmatic changes to the DB, written in Ruby, including code to back the changes out, and so on.

[Marc Peabody]

When I was new to Rails I was pretty confused by the term "migration" because I always understood it to mean "Labor intensive SQL project to move DATA from location A to location B."

In Rails, "migration" just means "tweak the database schema a little bit" and sometimes it also means "move some data around while changing the schema" but the moving part tends to be fairly rare - pretty much only when doing a refactoring to the domain model.

Since Rails is an agile, build-as-you-go framework, migrations typically just add more tables and columns to an existing schema.