einundzwanzig-app/app/Http/Requests/Api/UpdateCourseRequest.php

<?php

namespace App\Http\Requests\Api;

use Illuminate\Foundation\Http\FormRequest;

class UpdateCourseRequest extends FormRequest
{
    public function authorize(): bool
    {
        return $this->user()->can('update', $this->route('course'));
    }

    /**
     * @return array<string, array<int, string>>
     */
    public function rules(): array
    {
        return [
            'name' => ['sometimes', 'required', 'string', 'max:255'],
            'lecturer_id' => ['sometimes', 'required', 'integer', 'exists:lecturers,id'],
            'description' => ['sometimes', 'nullable', 'string'],
        ];
    }

    /**
     * @return array<string, string>
     */
    public function messages(): array
    {
        return [
            'lecturer_id.exists' => 'Der angegebene Referent existiert nicht.',
        ];
    }
}