php - fetch() 方法出错

Question

我收到错误声明:

Call to a member function fetch() on a non-object in /home/content/26/11794426/html/practice/home.php on line 16

基于此，我相信 mysql 查询没有创建对象。但是，我直接从书中复制代码，所以我很困惑为什么会出现错误。是 fetch() 部分本身还是查询？

另外，我将 sql 查询复制并粘贴到 phpmyadmin 的数据库中，所以我认为那里没有错误，但我不排除它。

有什么想法吗？

<?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);

?>

这就是我的database.php 文件的样子:

<?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'];