reduce.ex

  # This function is only included for context - it creates a multi-operation transaction structure
  # for a single widget and its associated options
  def create_multi(params, operation_type, widget, identifier \\ :widget) do
    changeset = Widget.changeset(widget, params)

    apply(Ecto.Multi, operation_type, [Ecto.Multi.new(), identifier, changeset])
    |> maybe_merge_widget_options(identifier, params)
  end

  # Here's the usage of reduce. Notice the map + "mappend"(?) inside the reduce. If Ecto.Multi
  # implemented Collectable, this would be a ripe opportunity for Enum.into/2...
  def create_bulk_multi(widgets) do
    Enum.reduce(widgets, Ecto.Multi.new(), 
      fn widget, multi_acc ->
        unique_key = unique_multi_key(:widget)

        widget_multi = create_multi(widget, :insert, %Widget{}, unique_key)
        Ecto.Multi.append(multi_acc, widget_multi)
      end
     )
  end