I've developed a useful feature in KeystoneJS that lets you populate a relationship from either side, while only storing the data on one side, and am looking for feedback on whether it is something that could / should be brought back into mongoose itself. (It might be possible to add as a separate package but I suspect there'd be too much rewriting of mongoose internals for that to be a good idea).
I've added this as an issue in mongoose for consideration: #1888 but am leaving this gist in place because the examples are easier to read.
I've used Posts and Categories as a basic, contrived example to demonstrate what I'm talking about here; in reality you'd rarely load all the posts for a category but there are other real world cases where it's less unreasonable you'd want to do this, and Posts + Categories is an easy way to demo it.
The built-in population feature is really useful; not just for