Question

The Situation

I have a table in a DB that contains job types, basically defined by a label and a price. I’m trying to do a simple SELECT * FROM jobtype but I can’t seem to get it to work, although I’ve use the same block over and over again in the rest of the code. The main difference here, is that it is a singleton trying to execute the function.

The problem is that as soon as I uncomment the line $rs_job_types = mysql_query($query_job_types, $vtconnection) or die(mysql_error()); the page will stop loading at this particular point in the code.

The Code

Following is the code of my function getJobTypes():

require_once('Connections/vtconnection.php');
class JobTypes extends Singleton{
    static private $job_types;

    public static function getJobTypes(){
        if (self::$job_types == null){
            echo 'DEBUG: For now, $job_types is NULL.'."\n";
            mysql_select_db($database_vtconnection, $vtconnection);
            $query_job_types = 'SELECT * FROM jobtype';
            $rs_job_types = mysql_query($query_job_types, $vtconnection) or die(mysql_error());

            while ($rs_row = mysql_fetch_assoc($rs_job_types)){
                // let the job type identifier in the db be its index in our array
                self::$job_types[$rs_row['id']]['label'] = $rs_row['label']; // job type label
                self::$job_types[$rs_row['id']]['price'] = $rs_row['price']; // job type price
            }
            if (self::$job_types != null) echo 'DEBUG: $job_types has been populated.'."\n";
        }
        return self::$job_types;
    }
}

Which I am calling like so:

$jt = JobTypes::getJobTypes();

Here is my singleton pattern:

class Singleton{
    private static $instances = array();

    final private function __construct(){
    }

    final public function __clone(){
        trigger_error('You don\'t clone a singleton!', E_USER_ERROR);
    }

    final public static function getInstance(){
        $c = get_called_class();
        if(!isset(self::$instances[$c])){
            self::$instances[$c] = new $c;
        }
        return self::$instances[$c];
    }
}

I have turned the problem in my head, commented everything inside the getJobtypes() function and uncommented step by step. I found out the problem does happen with the mysql_query() line, just can’t seem to work out why. Is something obviously wrong in my code?

---

Solved

As suggested here, I used global $vtconnection,$database_vtconnection; at the start of my static function and all went smooth. It is not an optimal solution but it pointed out the scope issue which I will now try to resolve.

I also got rid of the singleton pattern.

Answer 1

Well the most obvious thing is $database_vtconnection $vtconnection are defined nowhere in your getJobTypes function. If they’re part of the class, you need $this (object) or self (static) references. More likely it looks like you’re trying to use global variables, in which case you have to pull them into the scope of the function.

mysql_select_db can auto-connect (if $vtconnection isn’t supplied) but only if it knows how – there’s a previous connection (or possible INI config with db/host/user/pass).

To pull them into scope you need to add the line at the beginning of the function:

global $vtconnection,$database_vtconnection;`

… Or use the $GLOBALS superglobal array:

mysql_select_db($GLOBALS["database_vtconnection"],$GLOBALS["vtconnection"]);

For the record using globals isn’t a particularly good solution.