requiredIf()

requiredIf($field, $value) makes a field required when the other field strictly equals the given value.

$rules->string('companyName')
    ->optional()
    ->requiredIf('accountType', 'business');

The comparison is strict and the field is required only when the condition matches. Conditional rules need the DTO object, so use them in registered object validation, Rule::on(), or Rule::for().

$user = new User();
$user->accountType = 'business';
$user->companyName = '';

$error = Rule::for($user)
    ->string('companyName')
    ->optional()
    ->requiredIf('accountType', 'business')
    ->validate();

If accountType is not business, an empty companyName is allowed because the rule is also marked optional().

For conditions based on multiple fields, pass a closure instead. It receives the object currently being validated:

$rule = Rule::for($order)
    ->string('internationalCode')
    ->optional()
    ->requiredIf(static fn (Order $order): bool =>
        $order->shippingMethod === 'business' && $order->isInternational
    );

The closure form is also available on requiredUnless(), prohibitedIf(), and prohibitedUnless().