AshMoney and Phoenix inputs - how to show validation errors?

Dear community :wave:t2:

I have an Ash resource with money attributes using ash_money, a thin wrapper around ex_money. I’ve been looking into the question of Phoenix inputs for money attributes and I think that there may be an opportunity for value to the community in large here.

The “tricky” part here is that the Money type is a composite of:

  • amount and
  • currency.

I have managed to dig up a Discord message between @zachdaniel and another user regarding this very issue and that was immensely useful (usually is :slightly_smiling_face:), see the code (completely) inspired by Zach’s response in the mentioned exchange below.

I’m looking into the issue of showing validation errors currently. However, I would think that this is an issue that could be generalised by better skilled people. This should be a really common use case since… everything comes down to money in the end :man_shrugging:t3:

The resource

attributes do
    # yada yada
    attribute :amount, :money, allow_nil?: false, public?: true

The inputs

There are two inputs for the attribute, one for the amount and another for the currency.

Note how the value attribute is extracted with helper functions.

  id={ <> "_amount_amount"}
  name={ <> "[amount][amount]"}

  id={ <> "_amount_currency"}
  name={ <> "[amount][currency]"}

The code

The amount and currency values are extracted using the helper functions amount/1 and currency/1 respectively.

defp currency(%{currency: currency}), do: currency
defp currency(%{"currency" => currency}), do: currency

defp currency(_value), do: nil

defp amount(%{amount: amount}), do: amount
defp amount(%{"amount" => amount}), do: amount

defp amount(_), do: nil

A general solution to a general problem?

@zachdaniel mentioned this in the subsequent message in the exchange I linked to above:

I think we need to improve the story for this kind of thing in AshPhoenix , will need to do some thinking on it. But the above will work though

There are other ways to work around these kinds of limitations, so if you get in a pickle what you can do is basically modify the params before they get into your form, and assign some values to correspond to the value.

How would you go about showing errors?

While the big brains ponder the elegant and general solutions to this, I – and I like think others as well – would be very happy to hear any thoughts on how you would handle showing the validation errors for :amount and :currency in the example above :slightly_smiling_face:

Thank you in advance and have a nice day :pray:t3:

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Something to try is adding the transform_errors option when creating the form. You can then check the path and field of each error and rewrite it to be a field in the form. Not super helpful but I’m not at a computer and it may be enough to get you on the right track :slight_smile:

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A while ago I added a similar solution of a “composite input” component (updated gist) in this discussion in the ex_money repo, but I also noticed that the error feedback experience was not that great when using this component in forms (see this issue))… :confused:

So I’m also looking for some nice solution to this problem…

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Thank you for taking the time to mention transform_errors! I tried to simplify my post by leaving out the transform_errors calls I already use for localising my custom Ash resource validations.

Btw, obviously not Ash specific but I wanted this to show up for any future community members searching for this or a similar issue.

The GitHub issue in LiveView’s repo that @Wigny linked to is rather spot on for this.

Many thanks @Wigny!

This was really spot on, and far more insightful than my own look into the matter. I’m glad that you opened the issue and I read it with great interest.

Will subscribe to any updates. I guess it would be practical for the community to record any resolution in this thread as well :pray: