Checked ActiveRecord, DataMapper, Sequel: some use globals (static variables) some require open db connection before loading source file with models. What ORM is better to u
DataMapper is designed for multi-database use.
You can set up multiple repositories just by saying something like DataMapper.setup(:repository_one, "mysql://localhost/my_db_name").
DataMapper then tracks all the repositories that have been setup in a hash that you can reference and use for scoping:
DataMapper.repository(:repository_one){ MyModel.all }
(The default scope just being DataMapper.repository, which you can set up by saying DataMapper.setup(:default, "postgres://localhost/my_primary_db") or the like)