Input validation exclusive or - php

Question

I have a model called Answer.
This model has two possible relations. A Question or a Product.
But, Answer should only ever have one relation. Either Question or Product.
There is a form to create answers.
This form has three inputs. two of them are <select> inputs. The other is a text input, called name.
I want my validation to only allow one to be filled out.
My current validation:
$validator = Validator::make(
Input::all(),
array('name' => array('required'))
);
$validator->sometimes('product', array('required', 'numeric'), function ($input) {
return !is_numeric($input->question);
});
$validator->sometimes('question', array('required', 'numeric'), function ($input) {
return !is_numeric($input->product);
});
Requires at least one of the selected to be filled out, but will also allow two.
So, my question is: How can I change my validation to only allow one of the selects to be filled out.
But one of them must always be filled out.
Select 1:
<select name="question" class="form-control">
<option>None</option>
<option value="1" selected="selected">Question 1</option>
<option value="2">Question 2</option>
</select>
Select 2:
<select name="product" class="form-control">
<option>None</option>
<option value="2" selected="selected">Product 1</option>
<option value="3">Product 2</option>
</select>

Answer 1

#Razor's custom XOR validation rule is pretty nice, but there's another route if you don't want to create a custom rule. You can add values to Input representing your constraints, using Input::merge, then use those for validation:
Input::merge(array(
'hasBoth' => Input::has('product') && Input::has('question'),
'hasNeither' => !Input::has('product') && !Input::has('question')
));
$validator = Validator::make(
Input::all(), array(
'name' => 'required',
'hasNeither' => 'size:0',
'hasBoth' => 'size:0',
), array(
'hasNeither.size' => 'A question or a product is required.',
'hasBoth.size' => 'You cannot choose both a question and a product.'
)
);
You should still change the empty value in your form to <option value=''>None</option>.
Unlike using an XOR comparison, this method allows you to return separate error messages for no values vs. two values without any further error checking.

Answer 2

First off. You must specify an empty value in "None" option:
<option value=''>None</option>
You are looking for XOR operator, you need to create a custom validation rule in this case:
Validator::extendImplicit('xor', function($attribute, $value, $parameters)
{
if( $value XOR app('request')->get($parameters[0]))
return true;
return false;
});
Validator::replacer('xor', function($message, $attribute, $rule, $parameters)
{
// add indefinite articles
$IAattribute = (stristr('aeiou', $attribute[0]) ? 'an ' : 'a ') . $attribute;
$parameters[0] = (stristr('aeiou', $parameters[0][0]) ? 'an ' : 'a ') . $parameters[0];
if(app('request')->get($attribute))
return 'You cannot choose both '.$IAattribute.' and '.$parameters[0].'.';
return $IAattribute.' or '.$parameters[0].' is required.';
});
$validator = Validator::make(
app('request')->all(),
array('name' => array('required')
,'product' => array('xor:question')
));

Answer 3

The required_without validation rule might be what you want:
The field under validation must be present only when any of the other
specified fields are not present.
Set the question field to required_without:product and the product field to required_without:question.

Answer 4

Answers are a little old now. Today laravel brings some prohibition-rules which will resolve your problems without any hacks.
For your validation that means:
return [
'question' => 'nullable|required_without:product',
'product' => ['nullable',
Rule::prohibitedIf(fn() => $this->question != '')]
Both selects need an item with empty-value, with a text/label you like. Like this:
<select>
<option value="">Foo</option>
</select>
Like this one of the both always need to be set. But its not possible that both are set.
See here: https://laravel.com/docs/9.x/validation#rule-prohibited