Validate only alphanumeric characters in Laravel

Question

I have the following code in my Laravel 5 app:

public function store(Request $request){
    $this->validate($request,          


        

Answer 1

use laravel rule,

    public function store(Request $request){
    $this->validate($request, ['filename' => 'alpha_dash']);
}

Laravel validation rule for alpha numeric,dashes and undescore