Can't select id from different table in MySQL database - php

Question

I'm building a website where users should be able to input music artists and albums into a database. I have tables artists and albums in the musique database.
I'm trying to select artistId from artists and associate it with whatever album the user is trying to input. The artistId keeps coming back as 0, though. I think something is wrong with my SELECT statement, but I'm not totally sure.
Does anyone see a reason why this is happening?
inputalbum.php:
<?php
include "session.php";
include "db.php";
SessionClient::checkIfLoggedIn();
// Get list of artists to suggest
$conn = DB::connect();
$results = $conn->query("SELECT artistName FROM artists");
$artists = [];
while ($row = $results->fetch_assoc()) {
$artists[] = $row;
}
?>
<?php include "header.php"; ?>
<div class="container">
<h1>INSERT ALBUM</h1>
<form class="form" enctype="multipart/form-data" action="albumredir.php" method="POST">
<fieldset>
<label for ="artistName">Artist</label>
<input type="text" name="artistName">
<br>
<!-- <div>
Artists already in the database: <span>?</span>
</div> -->
<script>
// Transfer php array to js to use on the browser
var artists = <?php echo json_encode($artists) ?>;
// Grab the artist input field
var artistInput = document.querySelector('input[name="artists"]');
// Set an event for when they change to suggest artists
artistInput.oninput = function () {
var currentValue = artistInput.value;
var suggestedArtists = [];
artists.forEach(function (artist) {
var enteredArtists = currentValue.split(',');
if (artist.label.match(enteredTags[enteredArtists.length - 1].trim())) {
suggestedArtists.push(artist);
}
});
var suggestionString = suggestedArtists.map(t => t.label).join(',');
document.querySelector('div span').innerHTML = suggestionString;
}
</script>
<label for="albumName">Album Name:</label>
<input type="text" name="albumName" placeholder="Album One">
<br>
<label for="relDate">Release Date:</label>
<input type="date" name="relDate">
<br>
</fieldset>
<fieldset>
<input type="submit" name="submit" value="Submit">
</fieldset>
</form>
</div>
albumredir.php:
<?php
session_start();
$artistName = $_POST['artistName'];
$albumName = $_POST['albumName'];
$relDate = $_POST['relDate'];
$submit = $_POST['submit'];
include "db.php";
$conn = DB::connect();
$artistId = $conn->query("SELECT artistId FROM artists WHERE artistName = $artistName");
$stmt = $conn->prepare("INSERT INTO albums (artistId, userId, albumName, relDate) VALUES (?, ?, ?, ?)");
$stmt->bind_param(
"iiss",
$artistId,
$_SESSION['currentUser']['userId'],
$_POST['albumName'],
$_POST['relDate']
);
if(isset($_SESSION['currentUser']['userId']))
{
$currentUser = $_SESSION['currentUser']['userId'];
}
else
{
$currentUser = NULL;
}
if(isset($_POST['albumName']))
{
$albumName = $_POST['albumName'];
}
else
{
$albumName = NULL;
}
if(isset($_POST['relDate']))
{
$relDate = $_POST['relDate'];
}
else {
$relDate = NULL;
}
$stmt->execute();
// Close the connection
$conn->close();
// header('Location: index.php');
?>

Answer 1

$artistId = $conn->query is returning a result set, so you can't bind to it directly later when you try:
$stmt->bind_param(
"iiss",
$artistId,
you will need to fetch the artistId from the result set first.
In this example, I change the name of the result set from $artistId to $result for clarity.
$result = $conn->query("SELECT artistId FROM artists WHERE artistName = $artistName");
// get row from result
$row = $result->fetch_assoc();
// get artistID from row
$artistId = $row["artistId"];
$stmt = $conn->prepare("INSERT INTO albums (artistId, userId, albumName, relDate) VALUES (?, ?, ?, ?)");
$stmt->bind_param(
"iiss",
$artistId,
$_SESSION['currentUser']['userId'],
$_POST['albumName'],
$_POST['relDate']
);