Dynamic nested model in embeded field

Hello there!

I’m having a devil of a time getting a dynamic embedded schema to save in postgres.

So I started here, basically

But my core problem is that despite several iterations, when it goes to save it to the database, it throws

(UndefinedFunctionError) function :map.schema/1 is undefined (module :map is not available)

So in my hunt, I came across this package and it slimmed down the code, but I still have the same problem :(. It’s like ecto isn’t seeing the type update before it goes into schema. With your package the changeset automatically sets the type, which is really super nice, but for some reason I can’t get this to save to postgres:

## This is the latest iteration, of many attempts.

defmodule Geeks.Activities.Activity do
  @moduledoc false

  use Ecto.Schema
  import Ecto.Changeset
  import GatheringRole
  alias Geeks.Activities.Types

  embedded_schema do
    field :type, ActivityType
    field :title, :string
    field :max_participants, :integer
    field :next_start, :utc_datetime
    embeds_one :properties, :map
    embeds_many :rsvp, Geeks.Activities.ActivityRsvp
    embeds_many :history, Geeks.Activities.ActivityHistory do
      field :history_event, :string
      timestamps([types: :utc_datetime])
    timestamps([types: :utc_datetime])

  @all_fields ~w(type title max_participants next_start)a
  @required_fields ~w(type title)a
  defp properties_type(props_schema) do
        cardinality: :one,
        field: :properties,
        on_cast: &props_schema.changeset(&1, &2),
        on_replace: :update,
        owner: nil,
        related: props_schema,
        unique: true

  def create_changeset(%{ properties: props } = params) do
    {:ok, props_schema} = Types.get_schema(:ttrpg)
    props_cs = EctoMorph.generate_changeset(props, props_schema)
    case props_cs.valid? do
      true ->
        changeset =
          |> cast(params, @required_fields)
          |> Map.update!(:types, &Map.put(&1, :properties, properties_type(props_schema)))
          |> cast_embed(:properties)
          |> validate_required(@required_fields)
      false ->


  def create_changeset(%{} = params ) do
    create_changeset(%{params | properties: %{}})


And elsewhere, in the context:

  def add_activity(%Gathering{ activities: activities} = gathering, activity_params \\ %{properties: %{}}) do
   changeset = Ecto.Changeset.change(gathering)
   activity = Geeks.Activities.Activity.create_changeset(activity_params)
   case activity.valid? do
     true -> changeset = Ecto.Changeset.put_embed(changeset, :activities, activities ++ [activity])
             |> Geeks.Repo.update!
     false -> {:error, activity}

I did see this post: How to validate dynamic fields in embedded_schema

But it just seems like I’m missing something

I’m going to try to cross-post this to the elixir forums, but man it’s a brainweaver!