This is an example from one of the very useful “FullstackPhoenix” tutorials, namely:

# lib/tutorial/shop/data.ex
defmodule Tutorial.Shop.Data do
  use Ecto.Schema
  import Ecto.Changeset

  @primary_key false
  embedded_schema do
    field :size, :string
    field :color, :string
  end

  @doc false
  def changeset(option, attrs) do
    option
    |> cast(attrs, [:size, :color])
    |> validate_required([])
  end
end

When saving the record, which embeds_one of the above, the whole “embedded_schema” gets stored, including fields, which are not set. This seems to make sense to me. At least as default behaviour. Out of curiosity – the question: is there a switch/option/other simple method, which would make it store only the fields, which are actually used/set?