with Phoenix 1.8 generated changeset functions, with a third parameter being user_scope, how do you call cast_assoc ?

  def changeset(q, attrs, user_scope) do
    q
    |> cast(attrs, [:name])
    |> validate_required([:name])
    |> put_change(:user_id, user_scope.user.id)
    |> cast_assoc(:parts, user_scope) <<-- this does not work
  end

in parts.ex

  def changeset(part, attrs, user_scope) do
    part
    |> cast(attrs, [:name])
    |> validate_required([:name])
    |> put_change(:user_id, user_scope.user.id)
  end

do I need to implement an arity 2 changeset function ?
then tweak the param map to incorporate the user_id in it ?

like

  def embedded_changeset(part, attrs) do
    part
    |> cast(attrs, [:name,  :user_id])
    |> validate_required([:name :user_id])
  end