The read_attribute (version 6) / read_raw_attribute (version 7) fails to return a field from an embedded model if the parent was loaded with only (and the embedded model is listed in only).

Example:

class Model
include Mongoid::Document

embeds_one :inner_model
end

class InnerModel
 include Mongoid::Document

embedded_in :model

field :name, type: String
end

model = Model.create
model.create_inner_model(name: 'test')

model = Model.only(:inner_model).first
puts model['inner_model.name'] # <= this fails with ActiveModel::MissingAttributeError

It works with only('inner_model.name'), which is also tested in attributes_spec, but it's not really what I want to do - if I include a whole embedded model, I expect I can read any of its fields.

I'm willing to make a patch for both version 6 and 7, if you confirm that this is not intentional behavior.