Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result

I get the error when trying to run this:

<?php
require_once('includes/DbConnector.php');
$connector = new DbConnector();
$result = $connector->query('SELECT title,content FROM staff_vacancies ORDER BY ordering LIMIT 0,100');
// Get an array containing the results.
// Loop for each item in that array
while ($row = $connector->fetchArray($result)){

echo $row['title'].'</h3>';
echo $row['content'];
}
?>

I have a linked file: DbConnector.php:

<?php
////////////////////////////////////////////////////////////////////////////////////////
// Class: DbConnector
// Purpose: Connect to a database, MySQL version
///////////////////////////////////////////////////////////////////////////////////////
require_once 'SystemComponent.php';

class DbConnector extends SystemComponent {

var $theQuery;
var $link;

//*** Function: DbConnector, Purpose: Connect to the database ***
function DbConnector(){

    // Load settings from parent class
    $settings = SystemComponent::getSettings();

    // Get the main settings from the array we just loaded
    $host = $settings['dbhost'];
    $db = $settings['dbname'];
    $user = $settings['dbusername'];
    $pass = $settings['dbpassword'];

    //the settings
    $host = 'localhost';
    $db = 'xxx';
    $user = 'xxx';
    $pass = 'xxx';

    // Connect to the database
    $this->link = mysql_connect($host, $user, $pass);
    mysql_select_db($db);
    register_shutdown_function(array(&$this, 'close'));

}

//*** Function: query, Purpose: Execute a database query ***
function query($query) {
    $this->theQuery = $query;
    return mysql_query($query, $this->link);
}

//*** Function: getQuery, Purpose: Returns the last database query, for debugging ***
function getQuery() {
    return $this->theQuery;
}

//*** Function: getNumRows, Purpose: Return row count, MySQL version ***
function getNumRows($result) {
    return mysql_num_rows($result);
}

//*** Function: fetchArray, Purpose: Get array of query results ***
function fetchArray($result) {
    return mysql_fetch_array($result);
}

//*** Function: close, Purpose: Close the connection ***
function close() {
    mysql_close($this->link);
}


}
?>

Does anyone know what the problem is?

From stackoverflow

• Your query must have a problem which is causing $result to be an invalid resource.

  Try checking for mysql_error() after the line on which you run your query.

  Edit:

  In fact, I would alter your DBConnector class function query() to something like the following, so that an identifiable error is thrown when you have a bad query:

  function query($query) {
      $this->theQuery = $query;
      $queryId = mysql_query($query,$this->link);
      if (! $queryId) {
       throw new Exception(mysql_error().".  Query was:\n\n".$query."\n\nError number: ".mysql_errno();
      }
      return $queryId;
  }
  

• // Load settings from parent class
  $settings = SystemComponent::getSettings();
  
  // Get the main settings from the array we just loaded
  $host = $settings['dbhost'];
  $db = $settings['dbname'];
  $user = $settings['dbusername'];
  $pass = $settings['dbpassword'];
  
  //the settings
  $host = 'localhost';
  $db = 'xxx';
  $user = 'xxx';
  $pass = 'xxx';
  

  Did you mean to reassign the connection vars? OR was that a few lines of stub code you forgot to take out? Or just an example to show what $settings contains?

• Please provide the error from mysql_error(). Without that I can only guess... try escaping your field names?

  $result = $connector->query('SELECT `title`,`content` FROM `staff_vacancies` ORDER BY `ordering` LIMIT 0,100');