Creating a user directory based off an auto-incremented userID - php

Question

I am attempting to create a user directory that's name is equal to the user's 'id' which is an auto-incremented column in my database. that will later be used to store text files for the user to access. But, Every time I run this I get an error because $row is null.
For context, This code is run right after a user is inserted into the database.
I've tried checking that $conn is valid and that $username is the correct username. However, when I run createUserDir on an existing user everything works fine.
Code for creating a user (works fine but thought I would show the placement of function call):
function createUser($conn, $email, $username, $pwd) {
$sql = "INSERT INTO users (username, password, email) VALUES (?, ?, ?);";
$stmt = mysqli_stmt_init($conn);
if (!mysqli_stmt_prepare($stmt, $sql)) {
header("location: ../register.php?error=stmtfailure");
exit();
}
$hashpwd = password_hash($pwd, PASSWORD_DEFAULT);
mysqli_stmt_bind_param($stmt, "sss", $email, $hashpwd, $username);
mysqli_stmt_execute($stmt);
mysqli_stmt_close($stmt);
createUserDir($conn, $username);
header("location: ../login.php?error=none");
exit();
}
Creates a user directory:
function createUserDir($conn, $username) {
$sql = "SELECT id FROM users WHERE username = ?;";
$stmt = mysqli_stmt_init($conn);
if (!mysqli_stmt_prepare($stmt, $sql)) {
header("location: ../register.php?error=stmtfailure");
exit();
}
mysqli_stmt_bind_param($stmt, "s", $username);
mysqli_stmt_execute($stmt);
$stmtResult = mysqli_stmt_get_result($stmt);
$row = mysqli_fetch_assoc($stmtResult);
$uid = $row['id'];
mysqli_stmt_close($stmt);
if(mkdir("../data/users/$uid")) {
die('Failed to create user directory.');
}
}

Answer 1

while creating a record add some text inside of the column, like "NA" so it won't return an error and later update values in last, using $last_id = $conn->insert_id;
might sound silly but might be it will work