Prevent redundant ActiveRecord queries to find primary keys when you already have the foreign key: raise or warn when looking up an association to find its primary key, if that primary key is present on the original object as a foreign key.
Save Yourself the Trip will make (according to your preference) soft or loud noise if you mistakenly write (for example) apartment.building.id, and recommend using apartment.building_id instead.
Inspired by the far more useful Bullet, which does the same thing for N+1 queries.
Install the gem in your project, then run SaveYourselfTheTrip.on! after ActiveRecord classes are loaded.
Spelunking in legacy code, you tend to see a lot of inefficient ActiveRecord statements. Wanted something to catch them so they could quickly be refactored and save a few milliseconds.