Most ORMs don't let us do this, and it works well. Getting back the entire relation (rather than some sub-tuple) isn't the kind of expense that causes problems

Most ORMs don't let us do this, and it works well. Getting back the entire relation (rather than some sub-tuple) isn't the kind of expense that causes problems scaling. It chews up network bandwidth between the database and the API, but it's not more computationally expensive (asymptotically). And if my entities are dozens of columns wide, I'm probably not in 3NF anyway, so it'd be better to focus my efforts on getting there.