Use with Ancestry

Problem: You want to expose relationships that are not normal ActiveRecord associations, such as those created by Ancestry.

Solution: Use the eager_load_on_include: false flag, along with the class_name argument to explain what the real model table is.

class Tree
  has_ancestry
end

class TreeResource < JSONAPI::Resource
  relationship :subtree, to: :many, eager_load_on_include: false, class_name: "Tree"
  relationship :children, to: :many, eager_load_on_include: false, class_name: "Tree"
  relationship :parent, to: :one, always_include_linkage_data: true, eager_load_on_include: false, class_name: "Tree"
end

Thanks to Hugh Barrigan for this tip.