I couldnt find this active calling of the up method in the rails active record docs.
AddColumns.new.up
it seems like migrating is usually done by rake db:migrate commands and not directly with ruby.
so it seems to me that its better to have a plugin migrate dir and then make symlinks from it to the /discourse/db/migrate directory in the plugin.rb file. this way the rails infrastructure for migration can also be used with rollback. maybe add documentation to roll back the specific changes to the plugin readme. seems like its possible with something like this to rollback specific migrations:
rake db:migrate:down VERSION=20100905201547
https://stackoverflow.com/questions/3647685/how-to-rollback-a-specific-migration
I would be glad to get some comments on this. I also think that its not productive to just link to the custom fields. I want to use discourse to create a chinese-english dictionary. I cant rely on only custom fields for this.