如果存在数组,则需要Laravel validate array元素

return [
    'bar'      => 'nullable|bail|array|size:2',
    'bar.bing' => 'required_with:bar|numeric',
    'bar.bang' => 'required_with:bar|numeric',
]

Docs for required_with

在这种情况下我倾向于这样做

public function rules(): array
{
    $rules = [
        // ...
    ];

    if ($this->bar) {
        $rules['bar'] = 'array|size:2';
        $rules['bar.bing'] = 'required|numeric';
        $rules['bar.bang'] = 'required|numeric';
    }

    return $rules;
}