Hi, I’m using Ecto embedded schemas for input validation of a JSON API. Basically, I have a Plug.Router implementation that accepts JSON and casts the input data into an Elixir struct with Ecto:

  ...
  post "/validate" do
    payload = conn.body_params

    changeset = MyApp.Document.changeset(%MyApp.Document{}, payload)
    if changeset.valid? do
      document = Ecto.Changeset.apply_changes(changeset)
      IO.inspect(document)
      send_resp(conn, 200, "Payload: #{inspect(document)}\n")
    else
      IO.inspect(changeset.errors)
      send_resp(conn, 400, "Error 400: Bad Request: #{inspect(changeset.errors)}\n")
    end
  end
  ...

My current implementation of the Ecto schema for MyApp.Document is shown below.
As you can see, a Document embeds a bunch of children, which for simplicity’s sake is now just Text elements.

defmodule MyApp.Document do
  use Ecto.Schema
  import Ecto.Changeset

  @primary_key false
  embedded_schema do
    field :id, Ecto.UUID
    field :type, :string
    embeds_many :children, MyApp.Text
  end

  def changeset(document, attrs) do
    document
    |> cast(attrs, [:id, :type])
    |> cast_embed(:children)
    |> validate_required([:id, :type])
    |> validate_inclusion(:type, ["https://spec.nldoc.nl/Resource/Document"])
  end
end

defmodule MyApp.Text do
  use Ecto.Schema
  import Ecto.Changeset

  @primary_key false
  embedded_schema do
    field :id, Ecto.UUID
    field :type, :string
    field :text, :string
  end

  def changeset(text, attrs) do
    text
    |> cast(attrs, [:id, :type, :text])
    |> validate_required([:id, :type, :text])
    |> validate_inclusion(:type, ["https://spec.nldoc.nl/Resource/Text"])
  end
end

The casting in my router works in the sense that if I supply a document with an invalid id or where the type is incorrect, then changeset.errors in my router contains an error message and validation fails as expected (so 400 is returned).

However, if I have a similar problem in the any of the embedded objects, then the validation does indeed fail as expected, but changeset.errors in my router is empty.

How do I ensure that any errors originating from casting / validating embedded schemas (MyApp.Text), end up on the changeset returned by the parent (MyApp.Document)? Or how else do I ensure that changeset.errors in my router contains all validation errors, even from nested embeds?