php - Fatal error: Call to a member function prepare() on null

Question

I am trying to access a list of categories and their contents. I have a class called Categories. I keep getting this error. The weird thing is that I've used this same exact code in two other places so far with no problems. All I did here was reuse the code and change all the variables.

Fatal error: Call to a member function prepare() on null

Here is the code to my class:

    <?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();
    }
}

?>

And here is the code I am trying to call:

<?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');
?>

Answer 1

It looks like your $pdo variable is not initialized. I can't see in the code you've uploaded where you are initializing it.

Make sure you create a new PDO object in the global scope before calling the class methods. (You should declare it in the global scope because of how you implemented the methods inside the Category class).

$pdo = new PDO('mysql:host=localhost;dbname=test', $user, $pass);