Question

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 use in sinatra application that uses different databases.

Answer 1

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)