I've got this example of a has_one relation (by reference):

class Profile
  include Mongoid::Document

  has_one :graph
end

class Graph
  include Mongoid::Document
  field :labels, type: Array  

  belongs_to :profile

  scope :lightweight, without(:graph_file)
end

profile.graph.lightweight.labels  # => undefined method `lightweight' for #<Graph: ....>

I've tried this both with the latest head version as well as with gem version 2.4.11. According to the docs: All relation objects in Mongoid are proxies to the actual document or documents themselves... This doesn't seem to be the case here. The same goes for association extensions defined with a block on the has_one itself.

I do get the expected behavior (ability to invoke the scope through the proxy) when using a has_many association.