datamapper/dm-migrations — comment on commit cd9d62ee08b6615a2d1ab2482b24d72232d867a3
File:  line 0
By richmeyers:

Ticket link for those unfortunate to have found this issue the hard way: http://datamapper.lighthouseapp.com/projects/20609/tickets/1214

This fix should have been released in a bug fix 1.0 release.

To work around the failure, you have to define migrations and invoke migrate_up! (or whatever) on the same object. Datamapper includes DataMapper::MigrationRunner into the global namespace, thus if you call migrate globally you have to call migrate_up! globally as well (assuming this works, not tested).

I changed migration definition to read:

DataMapper.migration '2011-10-14T20:09:23Z', :change_commit_message_to_text do

and then invoke it like this:

DataMapper.migrate_up!