(De)serializing JSON documents into Structs: Just include `__struct__`? Seemingly not quite

[al2o3cr]

@MarcusRiemer

    field :presences, %{optional(Presence.id) => Presence.t()}
  end

  def build() do
    %__MODULE__{
      id: Ecto.UUID.generate(),
      name: "Some Guest",
      presences: %{
        "#{Ecto.UUID.generate()}": %Presence{

Nitpick: build here is not building the type that you’ve declared for presences - it produces a map with atom keys, but the type specifies Ecto.Uuid.t() keys.

You’d write it as (not tested, apologies if it’s wrong):

  def build() do
    %__MODULE__{
      id: Ecto.UUID.generate(),
      name: "Some Guest",
      presences: %{
        Ecto.UUID.generate() => %Presence{