Resource interacts with HasOne and HasMany differently

I have a model (User) that I want to expose on an API to a certain class of users. Those users will always have a given permission and expiration, so I want to set those on the server, rather than expose uneditable fields to the client.

class UserResource < JSONAPI::Resource
  has_many :permissions
  has_one  :expiration, foreign_key_on: :related

  before_create :add_defaults

  def add_defaults
    self.permissions << Permission.find_by(title: 'Admin')
    self.model.expiration = Expiration.new(date: Date.new(2015,12,30))
  end

I think it's odd that I need to call the underlying model in order to interact with has_one objects, and I suspect this is the case for created objects, but I haven't gotten that far yet. Ideally, I could call self.expiration= and I would get behavior similar to self.permissions<<.

Am I just using JSONAPI::Resource incorrectly, or is this something worth pursuing?

UserResourceのリレーション宣言とそのbefore_createコールバックから始め、has_many permissionsのインタラクションとhas_one expirationのインタラクションを比較します。リソースレベルで期待される割り当ておよび作成の動作を特定し、焦点を絞ったテストで、has_oneの処理が要求されたhas_manyと同様の動作に一致することを確認します。