Some context to avoid the XY Problem: I’m trying to expose some state which lives in an external API as a resource field.

Let’s say I have a User resource and I want to retrieve the URL for their Gravatar given their email. My understanding is that I can do this with a calculation

  calculations do
    calculate :gravatar_url, :string, User.Calculations.Gravatar
  end

defmodule MyApp.User.Calculations.Gravatar do
  use Ash.Calculation
  alias MyApp.GravatarAPI

  def calculate(users, _opts, _context) do
    Enum.map(users, fn user ->
      case GravatarAPI.fetch_url(user.email) do
        {:ok, url} -> url
        {:error, _} -> nil
      end
    end)
  end
end

The problem with this solution is that if I retrieve a list of users using, e.g., GraphQL, the current implementation just silently returns nil without letting the user know that, e.g., the API request failed for a specific user (which is something which can potentially be shown in GraphQL errors).

On the other hand, if I return {:error, :something} if anything fails a single failed API request makes the calculation fails for all the users.

Is there a way around this? Am I using the wrong Ash tool?

The other possibility I thought of is using a resource with no data layer instead of a calculation. n that case, if I call both Simple.set_data and Ash.Query.add_error does the whole query fails (so nothing gets exposed from GraphQL) or is the partial data shown alongside the error?