Question

In my opinion i have a weird problem. The part below works fine

$sql = "
    UPDATE 
        ".$table[0]."
    SET 
        p_title = '".$_POST['p_title']."', 
        p_date = '".$_POST['p_date']."' 
    WHERE 
        p_id = '".$_POST['p_id']."'
";
if(!$db->exec($sql)){
    echo($defaults->throwError('MySql error',$sql,implode(":",$db->errorInfo())));
}else{
    $defaults->writeLog($table,$db->lastInsertId(),'update');
}

But when i try the code below i get an ‘Fatal error: Call to a member function exec() on a non-object in’

class Defaults{
    [..]
    public function query($sql){
        if(!$db->exec($sql)){
            echo($defaults->throwError('MySql error',$sql,implode(":",$db->errorInfo())));
        }else{
            $defaults->writeLog($table,$db->lastInsertId(),'update');
        }
    }
    [..]
}

and then on my page

$defaults = new Defaults();
$defaults->query("
    UPDATE 
        ".$table[0]."
    SET 
        p_title = '".$_POST['p_title']."', 
        p_date = '".$_POST['p_date']."' 
    WHERE 
        p_id = '".$_POST['p_id']."'
");

How come?

Ah, it was about the $db in the class. However, when i do something like

public function query($sql){
    $db = new PDO($dbdata->hostname,$dbdata->username,$dbdata->password);
    if(!$db->exec($sql)){
        echo($defaults->throwError('MySql error',$sql,implode(":",$db->errorInfo())));
    }else{
        $defaults->writeLog($table,$db->lastInsertId(),'update');
    }
}

I get a nasty

Fatal error: Uncaught exception 'PDOException' 
with message 'invalid data source name' 
in /class.defaults.php:8 

Stack trace: 
#0 /class.defaults.php(8): PDO->__construct('', NULL, NULL) 
#1 /class.form.php(269): Defaults->query('?????????UPDATE...') 
#2 /module.projectbeheer.edit.php(25): Form->proceed('update', 'p_id', 'rows', Array, Array, '') 
#3 /class.content.php(16): include_once('/path/') 
#4 /administratie.php(72): Content->write('/BraamsArchief/...') 
#5 {main} thrown in /class.defaults.php on line 8

Answer 1

You must provide $db either as a global or as a class property. Otherwise, you cannot access it in the method scope.

So either:

public function query($sql) {
    global $db;
    // now you can use $db as you would in global scope
}

or else you have to set a class property (e.g. $this->db) with your database connection object and access it using $this->db in your method.

Note that if you use the global solution, you will need to ensure that the variable is always called $db when it is initially defined. Otherwise, your method may not be able to find it and you will get the same error.