How can I manually return or throw a validation error/exception in Laravel?

Question

Have a method that's importing CSV-data into a Database. I do some basic validation using

class CsvImportController extends Controller
{
    public function import(Request $request)
    {   
        $this->validate($request, [
            'csv_file' => 'required|mimes:csv,txt',
        ]);

But after that things can go wrong for more complex reasons, further down the rabbit hole, that throws exceptions of some sort. I can't write proper validation stuff to use with the validate method here, but, I really like how Laravel works when the validation fails and how easy it is to embed the error(s) into the blade view etc, so...

Is there a (preferably clean) way to manually tell Laravel that "I know I didn't use your validate method right now, but I'd really like you to expose this error here as if I did"? Is there something I can return, an exception I can wrap things with, or something?

try
{
    // Call the rabbit hole of an import method
}
catch(\Exception $e)
{
    // Can I return/throw something that to Laravel looks 
    // like a validation error and acts accordingly here?
}

Answer 1

As of laravel 5.5, the ValidationException class has a static method withMessages that you can use:

$error = \Illuminate\Validation\ValidationException::withMessages([
   'field_name_1' => ['Validation Message #1'],
   'field_name_2' => ['Validation Message #2'],
]);
throw $error;

I haven't tested this, but it should work.

Update

The message does not have to be wrapped in an array. You can also do:

use Illuminate\Validation\ValidationException;

throw ValidationException::withMessages(['field_name' => 'This value is incorrect']);