Confusing "Using validators with form inputs"

[wildfiremedia]

When I read the docs, I got confused. I was receiving an “invalid type” error because an empty string was being returned as null. Is that a valid error, or is it actually an invalid type error? How should I make it submit as an empty string instead?
I’m using z.discriminatedUnion('type', ...) but I’m still getting null for empty inputs. I’ve spent the whole day reading and I’m still not sure if I’m doing this correctly, for example, when submitting a new contact form, someone might leave a required field empty, and the hidden type is "create".

The form is submitted via Astro actions on the client side using plain JavaScript.

<form id="ci-form" action={actions.contact} method="post" class="grid gap-3">
        <input transition:persist type="text" name="name" placeholder="Name" pattern=".{3,100}" required />
        <input transition:persist type="email" name="email" placeholder="Email" min="8" maxlength="254" title="Email must be between 8 and 254 characters" required />
        <input type="hidden" name="type" value="create" />
        <button id="submit" type="submit">Send</button>
    </form>

accept: 'form',
    input: z.discriminatedUnion('type', [
        z.object({
            type: z.literal('create'),
            name: z.string().min(10, ''),
            email: z.string().email('').min(10,''),
        }),
    ]),

Error: Failed to validate: [ { "code": "invalid_type", "expected": "string", "received": "null", "path": [ "name" 

Using validators with form inputs

When your action is [configured to accept form data](https://docs.astro.build/en/reference/modules/astro-actions/#accept-property), you can use any Zod validators to validate your fields (e.g. z.coerce.date() for date inputs). Extension functions including .refine(), .transform(), and .pipe() are also supported on the z.object() validator.

Additionally, Astro provides special handling under the hood for your convenience to validate the following types of field inputs:

Inputs of type number can be validated using z.number()
Inputs of type checkbox can be validated using z.coerce.boolean()
Inputs of type file can be validated using z.instanceof(File)
Multiple inputs of the same name can be validated using z.array(/* validator */)
All other inputs can be validated using z.string()

When your form is submitted with empty inputs, the output type may not match your input validator. Empty values are converted to null except when validating arrays or booleans. For example, if an input of type text is submitted with an empty value, the result will be null instead of an empty string ("").

To apply a union of different validators, use the z.discriminatedUnion() wrapper to narrow the type based on a specific form field. This example accepts a form submission to either “create” or “update” a user, using the form field with the name type to determine which object to validate against:
`

[ArmandPhilippot]

I'm not sure what you mean with:

Is that a valid error, or is it actually an invalid type error?

There is an opened issue in the core repo (withastro/astro#13562) related to your issue. Currently, this is working as expected (while I agree this doesn't seem ideal): empty strings are converted to null.

That's why we have recently added:

When your form is submitted with empty inputs, the output type may not match your input validator. Empty values are converted to null except when validating arrays or booleans. For example, if an input of type text is submitted with an empty value, the result will be null instead of an empty string ("").

But maybe we can improve the wording if this is not clear enough?

I'm not sure what else we can do in docs regarding that... so we might need more details about what you were expecting to find in the docs?

In the meantime, I'm not sure what the workaround is:

• maybe using z.preprocess can help you convert it back to an empty string if the value is null?
• use a custom error message
• or simply fallback to a generic error message when you handle form actions errors

[ArmandPhilippot]

I'm closing this discussion because I don't think there is anything actionable in this repository and it seems this issue is already being tracked in core. If you need help finding the best workaround for your use case, feel free to create a support thread on our Discord server where you can get more opinions!