doc: Laravel: validation
Laravel 提供valide方法讓我們可以驗證request
$validatedData = $request->validate([
    'title' => ['required', 'unique:posts', 'max:255'],
    'body' => ['required'],
]);
這邊有所有validate提供的rule: Laravel: validate
而當我們fail validation, Laravel也會幫我們蒐集error
也可以透過ShareErrorsFromSession Middleware,使用$errors變數。
在blade裡面印出error來:
@if ($errors->any())
    <div class="alert alert-danger">
        <ul>
            @foreach ($errors->all() as $error)
                <li>{{ $error }}</li>
            @endforeach
        </ul>
    </div>
@endif