دریافت ارور   (حل شد )Call to a member function query() on a non-object

سلام دوستان لطفا این کد رو یه نگاهی بفرمایید موقع اجرا این ارور رو میده.

 Fatal error: Call to a member function query() on a non-object in C:\dev\workspace\web\mynotes\db.php on line 34

این هم کد دیتابیس

<?
class Db {
  private $connection;
  public function __constract($option=null){
    if($option!=null){
      $host=$option['host'];
      $user=$option['user'];
      $pass=$option['pass'];
      $name=$option['name'];
    } else {
      global $config;
      $host=$config['db']['host'];
      $user=$config['db']['user'];
      $pass=$config['db']['pass'];
      $name=$config['db']['name'];
    }
    $this->connection = new mysqli($host, $user, $pass, $name);
    if ($this->connection->connect_error) {
      echo "Connection failed: " . $this->connection->connect_error;
      exit;
    }
    $this->connection->query("SET NAMES 'utf8'");

  }
  public function first($sql) {
    $records=$this->query($sql);
    if($records==null){
      return null;
    }
    return $records[0];
  }

  public function query($sql) {
    $result = $this->connection->query($sql);
    dump($result);
    $records = array();
    if ($result->num_rows == 0) {
      return null;
    }
    while($row=$result->fetch_assoc()){
      $records[]=$row;
    }
    return $records;
  }
  public function connection() {
    return $this->connection;
  }

  public function close() {
    $this->connection->close();
  }
}
?>