致命错误：对空对象调用成员函数prepare()
我正在尝试访问类别及其内容的列表。我有一个名为“类别”的课程。我不断收到此错误。奇怪的是，到目前为止我已经在其他两个地方使用了同样的代码，没有任何问题。我在这里所做的只是重用代码并更改所有变量。
Fatal error: Call to a member function prepare() on null
这是我的类的代码：
<?php
class Category {
public function fetch_all() {
global $pdo;
$query = $pdo->prepare("SELECT * FROM dd_cat");
$query->execute();
return $query->fetchAll();
}
public function fetch_data($cat_id) {
global $pdo;
$query = $pdo->prepare("SELECT * FROM dd_cat WHERE cat_id = ?");
$query->bindValue(1, $cat_id);
$query->execute();
return $query->fetch();
}
}
?>
这是我尝试调用的代码：
<?php
session_start();
//Add session_start to top of each page//
require_once('includes/config.php');
require_once('includes/header.php');
include_once('includes/category.php');
?>
<link rel="stylesheet" href="css/dd.css">
<div id="menu">
<a class="item" href="drop_index.php">Home</a> -
<a class="item" href="create_topic.php">Create a topic</a> -
<a class="item" href="create_cat.php">Create a category</a>
<div id="userbar">
<?php
if( $user->is_logged_in() )
{
echo 'Hello ' . $_SESSION['user_name'] . '. Not you? <a href="logout.php">Sign out</a>';
}
else
{
echo '<a href="login.php">Sign in</a> or <a href="index.php">create an account</a>.';
}
?>
</div>
</div>
<?php
$category = new Category;
$categories = $category->fetch_all();
?>
<div id ="wrapper">
<h1>Categories</h1>
<section>
<ul>
<?php foreach ($categories as $category) { ?>
<li><a href="category.php?id=<?php echo $category['cat_id']; ?>">
<?php echo $category['cat_title']; ?></a>
</li>
<?php } ?>
</ul>
</section>
</div>
<?php
require_once('includes/footer.php');
?>
