Support unstructured data in nested forms

[torepettersen]

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Is your feature request related to a problem? Please describe.

Hi and thanks for your work on the Ash ecosystem ❤️

I am trying to create a form with unstructured nested data.

It is probably easiest explained with an example. I have a print where the fields that I should expect is defined in a template.

defmodule MyApp.Template do
  attributes do
    attribute :fields, {:array, :string}
  end
end

defmodule MyApp.Print do
  use Ash.Resource, domain: MyApp

  attributes do
    attribute :params, :map
  end

  actions do
    create :create do
      argument :template, MyApp.Template, allow_nil?: false
      argument :params, :map

      change fn changeset, _ ->
        template = Ash.Changeset.get_argument(changeset, :template)
        params = Ash.Changeset.get_argument(changeset, :params) || %{}

        changeset = Ash.Changeset.change_attribute(changeset, :params, params)

        Enum.reduce(template.fields, changeset, fn field, changeset ->
          if params[to_string(field)] in [nil, ""] do
            Ash.Changeset.add_error(changeset, field: field, message: "is required", path: [:params, field])
          else
            changeset
          end
        end)
      end
    end
  end
end

This code should work perfectly well, but now I am not able to find any way to make a form that would expect this data. The form should look something like this, but I don't see any way to setup a form with for_create.

<.inputs_for :let={params} field={@form[:params]}>
  <%= for field <- @template.fields do %>
    <.input field={params[field]} label={to_string(field)} />
  <% end %>
</.inputs_for>

Describe the solution you'd like

I vibe coded a solution that seems to work. I allowed for an API like this for creating the form:

form = AshPhoenix.Form.for_create(MyApp.Print, :create,
  domain: MyApp,
  forms: [params: [map?: true]]
)

Another alternative could be for the resource to be a map:

form = AshPhoenix.Form.for_create(MyApp.Print, :create,
  domain: MyApp,
  forms: [params: [resource: :map]]
)

I would also be super interested in your thoughts on alternative solutions.

Describe alternatives you've considered

No response

Additional context

I would be happy to create a PR with my current solution (of course after having cleaned up and reviewed the AI slop) or create a different solution, if you have any better ideas.

[zachdaniel]

I think we can honestly just handle an empty map as a value with no configuration at all. if you say inputs_for ... and there is no form for a given field, we can just assume its a map. If its nil, you get no forms. If its %{} you get a form, if its a list you get a list of forms over maps. Likely no need for additional options/configs?

[zachdaniel]

This is a great idea BTW 😄

[torepettersen]

Yes, that sounds even better 😊 If it would work like that, I neither see any reason to add any config for that.

I will give that a try.