Call to a member function query() on null PHP5.6

Question

I have cerb2 https://github.com/wgm/cerb2, it is an old ticketing system, it might looks weird but I have a a lot of knowledgeable information burried that I want to exploit. It is basically a PHP5/Mysql software with the mysql_connect() constructor

The main issues are queries that stay null at all times. The code base lays on Class definition and pseudo-variable $this to call a query method from another Class.

function CER_HASH_QUEUES(&$parent)
{
    global $session;
    global $queue_access; e();
    $this->db = (new cer_Database())->getInstance();
    $this->_parent = &$parent;

    if(empty($queue_access))
        $this->queue_access = new CER_QUEUE_ACCESS();
    else
        $this->queue_access = $queue_access;

    $sql = "SELECT q.queue_id, q.queue_name FROM queue q ORDER BY q.queue_name";

    $res = $this->_db->query($sql);

That last line ($res =… ) is stopping code execution with:

Fatal error: Call to a member function query() on null in

The Query method called from cer_Database.class looks like this ( https://raw.githubusercontent.com/wgm/cerb2/stable/cerberus-api/database/cer_Database.class.php )

function query($sqlString,$return_assoc=true)
{
    $config_db = (new cerConfiguration())->getInstance();

    if($return_assoc === true) $this->db->SetFetchMode(ADODB_FETCH_ASSOC);
    else $this->db->SetFetchMode(ADODB_FETCH_NUM);

    $res = $this->db->Execute($sqlString);

    if($cfg->settings["debug_mode"]) {
        $time_end = microtime();
        $query_time = microtime_diff($time_end,$time_start) * 1000; // convert secs to millisecs
        echo "<b>[CERBERUS QUERY]:</b> " . $sqlString . " (Ran: <b>" . sprintf("%0.3f",$query_time) . "ms</b>)<hr>";
    }

    return $res;
}

That last method depends on a second Class cerConfiguration() which relies on import_config_db() to construct the mysql connector. I am unable to figure out how to pass successfully my sql request following the design pattern carried by the relevant software here. The databases and the tables are OK on their sides, and the following php script is returning the sql query OK.

<?php
include('includes/third_party/adodb/adodb.inc.php');
$db = ADONewConnection('mysql'); 
$db->Connect("localhost", "user", "pass", "databasename");
$rs = $db->Execute('SELECT q.queue_id, q.queue_name FROM queue q ORDER BY q.queue_name');
print "<pre>";
print_r($rs->GetRows());
print "</pre>";

I guess without the object oriented design pattern understanding used by PHP I am going to struggle to resuscitate that old piece of software.

Any help, ideas very welcome. Yours.

Answer 1

Fatal error: Call to a member function query() on null in

You are likely to find further issues in your investigation, but the problem you're asking for help with is relatively simple.

The database property in the class is defined early on in your code as $this->db, but you are then trying to access it as $this->_db. The underscore makes it a different variable name, and thus it doesn't exist. So it is null, hence why you are getting Call to a member function query() on null.

To fix it, make sure you're using the same name for it throughout the class.