protected  $error;
    protected  $query;
    protected  $mysqli;
    
    public function __construct()
    {
        $this->error = false;
        $this->mysqli = new mysqli("localhost", "user", "password", "database");
        if ($mysqli->connect_errno) {
           $this->error = $mysqli->connect_errno;
        }
        
    }
    
    public function query ($query)
    {
        $result = $this->mysqli->query($query);
        $this->query = $query;
        
        if ($this->mysql->error) {
            $this->error = $this->mysql->error_list;
            
        } else {
            return $result;
        }
        
    }
    
    public function getError()
    {
        return $this->error;
    }
    
    public function getQuery()
    {
        return $this->query;
    }
    
}

///////////////Код
$db = new  DB ();
$db->query('SELECT *......');
if ($db->getError() !=false) {
    throw new \Exception('ErrorQuery:'.$db->getQuery().'---ErrorText'.$db->getError());
}