Relationships on Create for non ActiveRecord models

I guess more of a question.

I have this legacy app we are trying to slowly migrate to use jsonapi-resources. We have some bloated models we are splitting into smaller resources but also some models that point to Redis-backed models.

class RedisResource < JSONAPI::Resource
  attribute :attr_1
  attribute :attr_2

  # Override required. The underlying model is not based on
  # ActiveRecord.
  def self.find_by_key(key, options = {})
    context = options[:context]
    model = RedisModel.find(key)
    raise(JSONAPI::Exceptions::RecordNotFound, key) if model.nil?
    new(model, context)
  end
end

The problem though, is that somehow the relationship data is getting lost before reaching the Resource methods like: #replace_field(field_data).

All that info is available when I use an ActiveRecord model that uses the #belongs_to helper. But unsure what do I need to do/implement in my models to get the relationship assignment working.

Beginne mit RedisResource#find_by_key und verfolge, wie Beziehungsdaten für Ressourcen, die nicht auf ActiveRecord basieren, #replace_field(field_data) erreichen. Vergleiche diesen Pfad mit einer ActiveRecord-Ressource, die belongs_to verwendet; abgeschlossen ist die Aufgabe, wenn die Beziehungszuweisung des Issues für das Redis-gestützte Modell funktioniert und das relevante Verhalten durch Tests verifiziert ist.