class ActiveModel::ArraySerializer

def embedded_in_root_associations
  @object.each_with_object({}) do |item, hash|
    serializer_for(item).embedded_in_root_associations.each_pair do |type, objects|
      next if !objects || objects.flatten.empty?
      if hash.has_key?(type)
        case hash[type] when Hash
          hash[type].deep_merge!(objects){ |key, old, new| (Array(old) + Array(new)).uniq }
        else
          hash[type].concat(objects).uniq!
        end
      else
        hash[type] = objects
      end
    end
  end
end