Can I use struct in Phoenix.HTML.Form.params?

[rapidfsub]

defmodule Phoenix.Component do
  # ...
  def used_input?(%Phoenix.HTML.FormField{field: field, form: form}) do
    used_param?(form.params, field)
  end

  defp used_param?(_params, "_unused_" <> _), do: false

  defp used_param?(params, field) do
    field_str = "#{field}"
    unused_field_str = "_unused_#{field}"

    case params do
      %{^field_str => _, ^unused_field_str => _} -> false
      %{^field_str => %{} = nested} -> Enum.any?(Map.keys(nested), &used_param?(nested, &1))
      %{^field_str => _val} -> true
      %{} -> false
    end
  end
  # ...
end

In normal case, "the value of ^field_str key in params map" would be a string or a map with string keys.
But with ash_phoenix I can set it as a struct, i.e. Decimal.
With struct value, used_input?/1 always returns false, because nested is a map with only atom keys.

Is it proper to assign struct in params? Then this could be a bug.
Or, is it not intended to assign struct in params?

[SteffenDE]

Hey @rapidfsub,

the params of a %Phoenix.HTML.Form{} are supposed to have string keys, see https://hexdocs.pm/phoenix_html/Phoenix.HTML.Form.html#t:t/0. Can you clarify when you're seeing structs?

Some helpful things you could do are:

1. post what dbg(form, limit: :infinity, structs: false) returns
2. give more details how you create the form struct (e.g. what you pass to <.form for={}> or Phoenix.Component.to_form/2.

[rapidfsub]

@SteffenDE
It's not common case for normal phoenix app.
But with ash_phoenix, I can set the value in params to be a struct.
There are prepare_params and transform_params callback features in ash_phoenix.
It's my intention.

My question is "Is this allowed, or not recommended?"

[SteffenDE]

My question is "Is this allowed, or not recommended?"

The current typespec doesn't allow it: https://hexdocs.pm/phoenix_html/Phoenix.HTML.Form.html#t:t/0

params: %{required(binary()) => term()},

Is this officially encouraged by Ash anywhere?

[rapidfsub]

Is this officially encouraged by Ash anywhere?

No. But it is just possible to do.

[rapidfsub]

params: %{required(binary()) => term()},

@SteffenDE
I think typespec term() means, "struct is allowed", isn't it?

[SteffenDE]

You're right. The spec actually allows the values in the params to be anything, but for nested form values, LiveView expects those to be maps with string keys as well. I don't think this is something want to change, so I'd encourage you to ensure that you pass nested parameters a maps with string keys too.