Don’t give your fields the same name as any of your ActiveRecord classes or tables. It gave me a lot of problems (it didn’t work). For instance don’t use flavor in your candies table, if Flavor descends from ActiveRecord::Base. Use flavor_id (or anything other than flavor) instead. —LauTaarnskov
See DatabaseCompatibility? for database compatibility issues.
Be careful when using inheritance and multiple databases. Since it is implemented as single-table inheritance, child classes in a different db will not be picked up. However, you may be able to work around it by just creating a composite relation from the class inside the hierarchy to a class which references the second database. —DamonClinkscales