The code is fine, you're publicly chastising yourself over it for no reason. Mongoid had bad API semantics, and you did what you needed to do to make your code work. Then, you got rug pulled by a minor version update when they said "oopsie, we think these semantics make more sense!".
There might be an argument to make that your test suite could have caught this, however.
There might be an argument to make that your test suite could have caught this, however.