After spending a long time working on an NHibernate project where SchemaUpdate was not working against a MySQL database I spent some time looking into the issue. No errors were being spat out, I wasn’t even attempting to execute against the DB, just generate the script. It just looked like my DB was in synch with my mappings. It wasn’t.
With much scratching of head and several hours of trial and error I finally discovered this one irritating fact: If you have a table in your MySQL database that contains a mapped column of type LONGTEXT, don’t expect SchemaUpdate to work. TEXT works fine, so does MEDIUMTEXT (thank the maker – as TEXT is not long enough for this project), but not LONGTEXT.