I just added a patch to lighthouse that adds query attribute methods to associations. This makes associations behave more like any other attribute -
class Post < ActiveRecord::Base has_many :comments end
Post.new.comments? # => false
It adds query attribute methods to has_one (and through), has_many (and through), belongs_to (works with polymorphic) and has_and_belongs_to_many.
If that looks interesting / worthwhile, you can plus one it at:
Jeff Dean