Including composed relationships

I want to find out how to handle symmetric relationships with JSON API (and an Ember.js front-end). I have the following models:

class Person < ActiveRecord::Base
  has_many :friended, through: :friender_friendships, class_name: Person
  has_many :friended_by, through: :friended_friendships, source: :friended, class_name: Person
  has_many :friender_friendships, class_name: Friendship, foreign_key: "friender_id"
  has_many :friended_friendships, class_name: Friendship, foreign_key: "friended_id"

  def friendships
    Friendship.where("friender_id = ? OR friended_id = ?", id, id);
  end

end

class Friendship < ActiveRecord::Base
  belongs_to :friender, class_name: Person
  belongs_to :friended, class_name: Person
end

And the current resources:

class PersonResource < JSONAPI::Resource
  attributes :name
  relationship :friender, to: :many, class_name: "Person"
  relationship :friended_by, to: :many, class_name: "Person"
  relationship :friender_friendships, to: :many, class_name: "Friendship"
  relationship :friended_friendships, to: :many, class_name: "Friendship"
  relationship :friendships, to: :many, class_name: "Friendship"
end

class FriendshipResource < JSONAPI::Resource
  has_one :friender
  has_one :friended
  attributes :strength
end

When looking at a person's profile, I would like to show all friendships of that person, whether they are on the "friender" or the "friended" end of the relationship. When I'm fetching the person resource, I pass include=friendships so that all friendships are also returned and I don't need further requests to fetch friendship data.

However, that fails with the following error:

Association named 'friendships' was not found on Person; perhaps you misspelled it?

The reason for this is that jsonapi_resources eventually calls records.includes(relationship) (see here), and since friendships is not a real relationship, ActiveRecord throws an error.

I'm not really sure how to solve this with jsonapi_resources. It might be possible to turn friendships into a "real" hasMany relationship with AR, but I haven't found a way to do that (although it's possible my AR-fu is just lacking).

If not with AR, is there a way to solve this problem with jsonapi_resources? (without making an extra roundtrip to the server). Thank you.

Read lib/jsonapi/resource.rb#L533-L541 and the PersonResource and FriendshipResource definitions shown in the issue. Trace how include=friendships reaches records.includes(relationship), then determine what supported relationship or inclusion path can represent both friendship ends. Done means a person response includes all friendships in one request without the missing-association error.