class ActiveModel::Serializer::Associations::HasMany

def serialize_ids
  ids_key = "#{@name.to_s.singularize}_ids".to_sym
  if !option(:embed_key) && !source_serializer.respond_to?(@name.to_s) && source_serializer.object.respond_to?(ids_key)
    source_serializer.object.read_attribute_for_serialization(ids_key)
  else
    associated_object.map do |item|
      item.read_attribute_for_serialization(embed_key)
    end
  end
end