Laravel Request validation rules from PUT and POST

BookRequest.php

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class BookRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        switch ($this->method()) {
            case 'POST': {
                return [
                    'isbn' => "required|min:5|max:50",
                    'title' => 'required|max:100',
                    'edition' => 'numeric'
                ];
                }
            case 'PUT': {
                return [
                    'isbn' => "min:5|max:50",
                    'title' => 'max:100',
                    'edition' => 'numeric'
                ];
            }
        }
    }
}