Easy validation with symfony asserts

Validations.php

/** Use contraints **/
use Symfony\Component\Validator\Constraints\Email;
use Symfony\Component\Validator\Constraints\Regex;
use Symfony\Component\Validator\Constraints\Url;

/** Snapshot of a controller class **/
public function postAction(Request $request)
{
  $nameContainsErrors = $this->validator->validate($this->request->get('vendor_name'), new Regex(['pattern' => '/^[a-zA-Za0-9_-\s]+$/']));
  $urlContainsErrors = $this->validator->validate($this->request->get('vendor_url'), new Url());
  $emailContainsErrors = $this->validator->validate($this->request->get('vendor_email'), new Email());

  if ($nameContainsErrors->count()) {
    $this->request->getSession()->getFlashBag()->add('error',
    'Vendor name is not valid :' . $nameContainsErrors->get(0)->getInvalidValue());

     $this->request->getSession()->getFlashBag()->add('error', 'Vendor name allowed characters are case insensitive: a-z, digits: 0-9, whitespace, dash and underscore.');
  }

  if ($urlContainsErrors->count()) {
    $this->request->getSession()->getFlashBag()->add('error',
    'Vendor URL is not valid: ' . $urlContainsErrors->get(0)->getInvalidValue());

    $this->request->getSession()->getFlashBag()->add('error', 'URL must start with http:// or https://');
  }
}