A few months ago, I came cross this problem that I had 2 databases in my project, so that my model classes might map to tables from different databases. It took me a while to work out how to deal with it in ActiveRecord. Today, I had a same problem again, even though I still got my last project’s source code, it still took me a couple of hours to get everything right. So, I think I’d better to write it done, just in case that I will have to do it again or anyone else may need it. The Scenario: Database...