Nestru: serialize maps to nested structs

The Nestru library can convert a map of any shape into a model of nested structs according to given hints. And It can convert any nested struct into a map.

The library’s primary purpose is to serialize between JSON map and an application’s model that is a struct having other structs nested in it.

It comes from the idea to have no DSL and less custom code to parse JSONs as an alternative to full-fledged Ecto with schemaless changesets.

Works good in Jason <-> Nestru pair. The validation of the input can be done with pattern matching in Nestru callbacks. Or automated with using Domo library that validates the struct conformance to its @type t() and associated precondition.

See typical usage in via:

Run in Livebook

Shortly it looks like:

defmodule Order do
  @derive Nestru.Encoder
  defstruct [:id, :items, :total]

  # Giving a hint to Nestru how to process the items list of structs
  # and the total struct, other fields go to struct as is.
  defimpl Nestru.Decoder do
    def from_map_hint(_value, _context, _map) do
      {:ok, %{
        items: &Nestru.from_list_of_maps(&1, LineItem),
        total: Total

defmodule LineItem do
  @derive [Nestru.Decoder, Nestru.Encoder]
  defstruct [:amount]

defmodule Total do
  @derive [Nestru.Decoder, Nestru.Encoder]
  defstruct [:sum]

map = %{
  "id" => "A548",
  "items" => [%{"amount" => 150}, %{"amount" => 350}],
  "total" => %{"sum" => 500}

{:ok, model} = Nestru.from_map(map, Order)


    id: "A548",
    items: [%LineItemA{amount: 150}, %LineItemA{amount: 350}],
    total: %Total{sum: 500}

And going back to the map is as simple as that:

map = Nestru.to_map(model)


  id: "A548",
  items: [%{amount: 150}, %{amount: 350}],
  total: %{sum: 500}

More information here:


0.1.1 - November 13, 2021

  • Add has_key?/2 and get/3 map functions that lookup keys in maps both in a binary or an atom form.

  • Add the link to open in LiveBook :slightly_smiling_face:

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I needed exactly this two weeks ago, thanks for making it. :heart:

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This is 100% exactly the library I needed. Thank you! (and again the extra time you spent on the documentation).

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