How to correctly validate checklist field in laravel backpack?

I created a "checklist" field with the following definition:

$this->crud->addField(
                [   // Checklist
                    'label'     => '<b>IDIOMAS</b>',
                    'type'      => 'checklist',
                    'name'      => 'idiomas',
                    'entity'    => 'idiomas',
                    'attribute' => 'titulo',
                    'model'     => "App\Models\Idioma",
                    'pivot'     => false,
                    'number_of_columns' => 3,
                    'wrapper' => [
                        'class' => 'form-group col-md-6',
                    ],
                    'tab' => 'HABILIDADES',
                ]
            );

I tried to validate with the following rules:

'idiomas' => 'required|array|min:1',
//'idiomas.*' => 'required|integer|exists:idiomas,id',

With the intention of forcing at least some element to be required. I did a lot of tests, the first one was just to use the "required" option, but nothing worked.

Reviewing the form that prints in html, I see that at the end there is a hidden field as follows:

<input type="hidden" value="[]" name="idiomas">

So for validation we receive "[]" which is NOT an array and cannot be validated that way. Shouldn't it be an array that you send? Because now it is a string of 2 characters that skips the validation of "required". For the moment what I did was to set the rule:

'idiomas' => 'required|min:3'

And change the validation message with:

'idiomas.min' => 'Debe seleccionar al menos un elemento'

But I was left with the doubt: Is there a better way?

Is the way Backpack Laravel returns the value to validate correct?

Should it be an array?

Solution

I'm not familiar with Backpack, but if the hidden element's value at initialization is [] I'm willing to bet it posts its data as a JSON string. To validate it, you'd need to decode the JSON first and then add it back into the request object. Here's my suggestion:

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class MyRequest extends FormRequest
{
    protected function prepareForValidation(): void
    {
        // could also use $this->replace() if desired
        $this->merge([
            "idiomas_data" => json_decode($this->idiomas),
        ]);
    }

    public function rules(): array
    {
        return [
            "idiomas_data" => ["required", "array", "min:1"],
            "idiomas_data.*" => ["integer", "exists:idiomas"],
        ];
    }
}