Simple object sqli insert - php

Question

Hello I'd like to insert all from $_SESSION into rows $key with value $value
so something like foreach ($_SESSION as $key => $value) {}
Imlooking at:Best way to INSERT many values in mysqli?
name of rows in mysqli is same as names of given $key .I need to insert each $value in its $key (row)
Code:
$query = "INSERT INTO testtable VALUES (?)";
$stmt = $dbc->prepare($query);
$stmt->bind_param("s", $key);
$mysqli->query("START TRANSACTION");
foreach ($_SESSION as $key => $value) {
$stmt->execute();
}
$stmt->close();
$mysqli->query("COMMIT");

Answer 1

Your query has a syntax error, which you never bothered checking for:
$query = "INSERT INTO testtable podatki VALUES (?)";
^^^^^^^^^^^^^^^^^
If that's really the table name, then it should be quoted with backticks:
$query = "INSERT INTO `testtable podatki` VALUES (?)";
^-----------------^
if podatki is a field name, then it should be
$query = "INSERT INTO testtable (podatki) VALUES (?)";
^-------^
And also never assume that a DB operation succeeded. ALWAYS check for errors:
$stmt = $dbc->prepare($query);
if (!$stmt) {
die(mysqli_error($dbc));
}

Answer 2

The error is saying that you are trying to call a member function, namely bind_param(), on a non-object.
That means that this line:
$stmt = $dbc->prepare($query);
is not succeeding,
and thus you have an incorrect return value that is set as the value of $stmt
so when you try to call bind_param it fails because $stmt is not the type of object that it was expecting.