public function userExists($login) 
    {
        $userTable = $this->getServiceLocator()->get('MelisCoreTableUser');
        $data = $userTable->getEntryByField('usr_login', $login);
        $user = '';
        foreach($data as $val) 
        {
            $user = $val->usr_login;
        }
        
        if(!empty($user))
        {
            return true;
        }
        else 
        {
            return false;
        }
    }