Run a single migration file

Assuming fairly recent version of Rails you can always run:

rake db:migrate:up VERSION=20090408054532

Where version is the timestamp in the filename of the migration.

Edit: At some point over the last 8 years (I'm not sure what version) Rails added checks that prevent this from running if it has already been run. This is indicated by an entry in the schema_migrations table. To re-run it, simply execute rake db:migrate:redo VERSION=20090408054532 instead.

You can just run the code directly out of the ruby file:

rails console
>> require "db/migrate/20090408054532_add_foos.rb"
>> AddFoos.new.up

Note: Very old versions of rails may require AddFoos.up rather than AddFoos.new.up.

An alternative way (without IRB) which relies on the fact that require returns an array of class names:

script/runner 'require("db/migrate/20090408054532_add_foos.rb").first.constantize.up'

Note that if you do this, it won't update the schema_migrations table, but it seems like that's what you want anyway.

Additionally, if it can't find the file you may need to use require("./db/..." or try require_relative depending on your working directory

If you want to run it from console, this is what you are looking for:

$ rails console
irb(main)> require "#{Rails.root.to_s}/db/migrate/XXXXX_my_migration.rb"
irb(main)> AddFoo.migrate(:up)

I tried the other answers, but requiring without Rails.root didnt work for me.

Also, .migrate(:up) part forces the migration to rerun regardless if it has already run or not. This is useful for when you already ran a migration, have kinda undone it by messing around with the db and want a quick solution to have it up again.