Never ever ever use natural keys in your database

This may sound obvious, but it just bit me. The case was about mongoid and automagically wrapping ids as ObjectId. More on this case here - https://gist.github.com/teamon/28cc33a4d3298f98596f

And if someone uses natural key:
![](http://25.media.tumblr.com/tumblr_m7xxdcwS921r74ytao1_1280.jpg)