On a blustery March day five years ago, I locked arms with my mother and walked into a church in Maplewood, New Jersey to bury my brother. Bagpipes played "Amazing Grace." I remember shivering and worrying: that my dad would slip, my mom would collapse, and that I would botch the eulogy.

You read the Rails guide and thought you have understood the has_many :through association and polymorphic associations. Your app models needed both. Unfortunately, the guide didn't explain how to combine these two together. Wondering why on earth the guide would leave out the most important yet complicated part, you had no choice but try to put them together yourself hoping you would get it right.