How can I make this php database class more secure?

I'm using the following PHP MySQL database class. I'm curious as to what I could do to make it more secure. I'm happy with it so far, but without suggesting to "use PDO" what can I do to improve this currently?

    <?

    class DbConnector {

    public static function getInstance(){
   static $instance = null;
   if($instance === null){
      $instance = new DbConnector();
   }

   return $instance;
    }

    var $theQuery;
    var $link;

    function DbConnector() {

        $host = 'localhos开发者_如何转开发t';
        $db     = '';
        $user = '';
        $pass = '';

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

    function find($query) {
        $ret = mysql_query($query, $this->link);
        if (mysql_num_rows($ret) == 0)
            return array();
        $retArray = array();

        while ($row = mysql_fetch_array($ret))
            $retArray[] = $row;

        return $retArray;
    }

    function insert($query) {
        $ret = mysql_query($query, $this->link);

        if (mysql_affected_rows() < 1)
            return false;
        return true;
    }

    function query($query) {
        $this->theQuery = $query;
        return mysql_query($query, $this->link);
    }

    function fetchArray($result) {

        return mysql_fetch_array($result);
    }

    function close() {
        mysql_close($this->link);
    }

    function exists($query) {
        $ret = mysql_query($query, $this->link);
        if (mysql_num_rows($ret) == 0)
            return false;
    }

    function last_id($query) {
        return mysql_insert_id($query);
    }


}

?>

If you don't want to use something that would automatically escape strings for you, you should at least provide an escapeString($string) method (which would call mysql_real_escape_string()) that you can use to escape strings when composing the query.

If you want to start using PDO (highly recommended) then you will probably have different methods and won't need to include an escaping method.

As for general considerations:

• don't use var, but rather use public, protected or private (var has been deprecated as of PHP 5.0, and is currently an alias for public)
• the __construct() method is preferred instead of the method with the name of the class
• it would be better not to connect in the constructor, but rather only connect when you really need to connect in order to perform a query; a constructor should do as little as possible, and generally only initialize properties
• mysql_connect() and mysql_select_db() will return false if they cannot do what they're supposed to; you should throw an exception if that happens and catch it where you use the class
• the mysql_query() call in the find() and exists() methods might return something other than a resource (false for example) so you should check for that before calling mysql_num_rows()
• if you're not using $theQuery at all, you should remove it
• if you want to have access to $theQuery, you should make it private and provide a getQuery() accssor method
• if you're setting the $link property to the resource returned by mysql_connect(), you should use that property in all your mysql_* calls, such as the one at last_id()
• you should make $link private (as a rule of thumb, all properties should be private or protected, and accessor methods should be provided when needed - read about the concept of encapsulation)
• even though all methods are by default public, having an explicit public keyword before each of them will make things clearer

ok I hate PDO too, "my own code is my own risk, while others code is also your own risk". Anyway, if you will use this script without any cleaner I'm sure you will make your DB explode. you may want to take a look at others mysql database connection classes before starting your own:

take a look here