redirection when groupname is already used

app/dependencies.php

@@ -15,6 +15,7 @@ use Doctrine\Common\Cache\FilesystemCache;
 use Doctrine\ORM\EntityManager;
 use Doctrine\ORM\Mapping\Driver\AnnotationDriver;
 use Doctrine\ORM\Tools\Setup;
+
 use Slim\Views\Twig;
 use Slim\Flash\Messages;
 

src/Application/Actions/Group/CreateGroupAction.php

@@ -20,9 +20,17 @@ class CreateGroupAction extends GroupAction
         $groupname =  $parsedRequestBody['name'];
         $description = $parsedRequestBody['description'];
 
-        $group = new Group(null, $groupname, $description);
-        $userRepository->find($_SESSION['userId'])->addGroup($group);
-        $userRepository->find($_SESSION['userId'])->addGroupAdmin($group);
+        if ($this->groupRepository->findOneBy(array('name' =>  $groupname))){
+            return $this->twig->render(
+                $this->response, "/group/create_group.twig",
+                array(
+                    "name" => $groupname,
+                    "description" => $description,
+                    "message" => "Groupname already exist",
+                    "formstatus" => "error"
+                )
+            );
+        }
         $this->em->persist($group);
         $this->em->flush();