Error with fetch() method - php

Question

I am getting the error statement:
Call to a member function fetch() on a non-object in /home/content/26/11794426/html/practice/home.php on line 16
Based off this, I believe that the mysql query isn't making an object. However, I am copying my code directly from a book so I am confused why I'm getting an error. Is it the fetch() part itself or the query?
Also, the database I copied and pasted the sql query into the phpmyadmin so I don't think there is an error there, but I'm not ruling it out.
Any ideas?
<?php
require_once('database.php');
// Get category ID
if(!isset($category_id)) {
$category_id = $_GET['category_id'];
if (!isset($category_id)) {
$category_id = 1;
}
}
// Get name for current category
$query = "SELECT * FROM categories
WHERE categoryID = $category_id";
$category = $db->query($query);
$category = $category->fetch();
$category_name = $category['categoryName'];
// Get all categories
$query = 'SELECT * FROM categories
ORDER BY categoryID';
$categories = $db->query($query);
// Get products for selected category
$query = "SELECT * FROM products
WHERE categoryID = $category_id
ORDER BY productID";
$products = $db->query($query);
?>
this is what my database.php file looks like:
<?php
$dsn = 'mysql:host=guitarshop27.db.11794426.hostedresource.com;dbname = guitarshop27';
$username = 'changed';
$password = 'changed';
try {
$db = new PDO($dsn, $username, $password);
}catch (PDOException $e) {
$error_message = $e->getMessage();
include('database_error.php');
exit();
}
?>

Answer 1

$category = $db->query($query);
$categorys = $category->fetch();
$category_name = $categorys['categoryName'];

Answer 2

You can try it with fetch_assoc();
$query = "SELECT * FROM categories
WHERE categoryID = $category_id";
$category = $db->query($query);
$category = $category->fetch_assoc();
$category_name = $category['categoryName'];
But the problem is the database conection. Where is it defined?

Answer 3

Try to debug your Code and also add this add this Code
// Get name for current category
$query = "SELECT * FROM categories
WHERE categoryID = $category_id";
$category = $db->query($query);
echo mysql_nun_rows($category);
$categories = $category->fetch();
$category_name = $categories['categoryName'];
if you find still error then check your database connection