Subset of a model instance's collection

I need to get a subset of an objects collection. Sort of like
named_scope but for a specific model instance.

Foo has_many :bar
Bar has_many :buzz

I want all of the bars for a specific foo but I only want to consider
bars without buzz.

The best I can come up with is using a "select" { |bar| bar.buzzs.empty? }

Is there a better way to do this?