Hacking polymorphic has_many into AMS. (e.g has_many :tasks, embed: :ids, include: true, polymorphic: true)

active_model_serializer.rb

module ActiveModel
  class Serializer
    module Associations
      class HasMany

        def key_with_polymorphism
          return @name if !option(:key) && option(:polymorphic)
          key_without_polymorphism
        end
        alias_method_chain :key, :polymorphism

        def serialize_ids_with_polymorphism
          return associated_object.map do |item|
            {id: item.id, type: item.type}
          end if option(:polymorphic)
          serialize_ids_without_polymorphism
        end
        alias_method_chain :serialize_ids, :polymorphism

      end
    end
  end
end