jonatw/shortUrl — comment on commit 7318bfe6aaa5a5cf688379756ad7cdaa1002e376
File: db/migrate/20111227194032_create_url_data.rb line 15
By marsz:

in Rails 3.1 (but u use rails 3.0.9), the migration class (this class) only define self.change to replace self.up & self.down
so that u just code what u want to do and rails will parse ur code for rollback undo

for example, in this class will be:

```ruby
def self.change
create_table :url_data do |t|
....
end
end

# no self.up & self.down
```

when executing "rake db:migrate", it will create table
executing "rake db:rollback", it will drop table