public function isRoleScopePresentOnce(ExecutionContextInterface $context) 
    {
        $roleScopesId = array_map(function(RoleScope $roleScope) {
                    return $roleScope->getId();
                }, 
                $this->getRoleScopes()->toArray());
        $countedIds = array_count_values($roleScopesId);
        
        foreach ($countedIds as $id => $nb) {
            if ($nb > 1) {
                $context->buildViolation("A permission is already present "
                        . "for the same role and scope")
                        ->addViolation();
            }
        }
    }