I'm going to describe a weird problem I faced when using ActiveRecord today. To protect the innocent, I'm not going to talk about the app I'm actually working on but will instead discuss a hypothetical but isomorphic database design for a clone of the popular blogging platform Tumblr.
Tumblr lets you publish various different sorts of content. We might be tempted to shove all these types in a big STI table, but the types are all quite different from one another and so we give them their own tables.