ActiveRecord database schema migration info is stored in the main database, so that if one needs to manually hack a migration (fastforward/rewind), just update
TABLENAME\_schema\_infos column ‘version’ to a new value and manually change your schema.
Next ‘boot’ may generate (or not) new migrations.
riverside=# select * from foobar_schema_infos;
id | version\n—+———
1 | 1.4
In a self note, forget not to set option :id => false on join tables for has_and_belongs_to_many relations.