Catchable fatal error: Object of class PDOStatement could not be converted to string in line 114

Question

I'm trying to add some data to my database, but I'm getting the error Catchable fatal error: Object of class PDOStatement could not be converted to string in /var/www/mandje.php on line 114. This is the code I'm using:

 foreach($_SESSION["cart"] as $id => $value){

        $query = $db->query('SELECT * FROM Producten WHERE ProductID ="'.$id.'" ');
        $query->execute();

        while($row = $query->fetch(PDO::FETCH_ASSOC)){
            $price = $row['Prijs'];
            $ProductID = $row['ProductID'];
            }
        $sql="INSERT INTO Bestellingsdetail( Bestelnummer, ProductID, Aantal, Prijs)
        VALUES ($max,$ProductID,$value,$price)";      //<---- line 114
        $count = $db->execute($sql);

I don't really get what's going wrong here. Any help would be much appreciated :)

Answer 1

In the comments, you show the following:

$query = $db->query('SELECT MAX( Bestelnummer ) FROM Bestellingsdetail');
$query->execute();
$max = $query;
$max++;

This is not how you get the result from a query. You are setting $max to a PDOStatement object. You need to fetch() the result in order to use it.

// I've added "AS maxval" to make it easier to get the row
$query = $db->query('SELECT MAX(Bestelnummer) AS maxval FROM Bestellingsdetail');
$max_row = $query->fetch(PDO::FETCH_ASSOC);

$max = $max_row['maxval'];
$max++;

Docs: http://www.php.net/pdo.query

P.S. $query->execute(); is only needed for prepared statements. query() will execute the query immediately.