I found that I was unable to migrate into postgres when defining a binary property because the column was being defined with the default length.
Currently TEXT, CLOB and NVARCHAR were ignoring the length so I've added bytea to this list.
Ignore the length property for bytea columns.
will that see a release one day ? kind of difficult to monkey patch this to get datamapper migration working on heroku: http://stackoverflow.com/questions/10154641/removing-limit-from-binary-column-for-postgresql-in-datamapper