I keep forgetting the rails generator syntax for migrations :X  I can never find just a quick easy guide for it – so I thought I’d write one up!

Instructions

1. cd …
   obviously first make sure your in the main project folder in the console
2. export RAILS_ENV=environment
   Also, make sure you’re in the right environment, you will probably want to make the change first in your test or development environment and then put it to production
3. rails g migration AddColumnToModel column_name:column_type
   Here’s the main part, on  older versions rails g migration will be script/generate migration.  The “AddColumnToModel” syntax is important and should relate to the migration you’re making like “AddEmailToUser” and then at the end you can add a “column_name:column_type” reference for each column you want to add, for instance with the last example you would put “email:string“
4. rake db:migrate
   run the migration and add those columns to the database!  You’ll probably want to review the migration that was generated first though – it’ll be the latest file in the …/db/migrate directory
   

AND MAKE SURE TO RESTART YOUR SERVER AFTER MAKING A CHANGE

Column Types

• binary: for files/ data blob
• boolean: true/false
• date: only date: (year, month, day)
• datetime: date + time
• decimal: precise decimal numbers – for when math neds to be accurate
• float: decimal numbers
• integer: whole numbers
• string: 255 max alphanumeric characters
• text: unlimited alphanumeric characters
• time: only time (hours, minutes, seconds)
• timestamp: same as datetime

 

And, if you make a mistake a quick way to go back and fix it is “rake db:migrate:redo” that will undo your last change, and re-run it.

Also, if you want to only run “rake db:migrate:up VERSION=20090408054532”

In a pinch you can also run a migration by hand in the console with the following format:
ActiveRecord::Migration.add_column :table, :column_name, :column_type

References:
http://stackoverflow.com/questions/11889048/is-there-documentation-for-the-rails-column-types
http://stackoverflow.com/questions/15162055/rails-generate-migration
http://stackoverflow.com/questions/7694487/ruby-on-rails-how-can-i-revert-a-migration-with-rake-dbmigrate