With these modules:

defmodule Foo do
  use Ecto.Schema
  import Ecto.Changeset

  schema "foo" do
    field(:name, :string, null: false)
    embeds_many(:bars, __MODULE__.Bar, on_replace: :delete)
  end

  def changeset(model, params \\ %{}) do
    model
    |> cast(params, [:name])
    |> cast_embed(:bars)
    |> validate_required([:name, :bars])
  end
end

defmodule Foo.Bar do
  use Ecto.Schema

  embedded_schema do
    field(:bar, :string, null: false)
  end
end

I expect the following line to return a “can’t be blank” error for the :bars field:

%Foo{} |> Foo.changeset(%{name: "foo"})

But instead, I got a valid changeset.

How can I make sure that :bars is present in the changeset?

I already tried cast_embed(:bars, required: true) but it doesn’t help.