Why am I getting a \"Fatal error: Call to a member function prepare() on null\" when using PDO in my PHP code?

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

Introduction

When attempting to interact with a database using a PHP object-oriented approach, encountering the "Fatal error: Call to a member function prepare() on null" can be frustrating. This error indicates that the PHP script is trying to access a method (in this case, the prepare() method) of an object that hasn't been properly instantiated or initialized.

Issue Analysis

The error provided in the question suggests that the $pdo variable is null when the prepare() method of the Category class is called. This indicates that the PDO object, which is used to connect to and interact with the database, hasn't been created in the global scope.

Solution

To resolve the error, the PDO object must be properly initialized and connected to the database. The following code can be added to the top of the script, outside any function or class definition:

<code class="php">$pdo = new PDO('mysql:host=localhost;dbname=test', $user, $pass);</code>

Replace localhost with the name of your database server, test with the database name, $user with the database username, and $pass with the database password.

This code creates a new PDO object and connects it to the database. Now, the $pdo variable will be available to all methods within the Category class, and the prepare() method can be called without encountering an error.

Additional Notes

1. Global Scope:
The $pdo variable should be declared in the global scope to ensure it's accessible to all methods within the Category class. Methods defined within a class can only access variables that are declared globally or passed as arguments to the method.

2. Error Origin:
The code provided in the question doesn't include the line where the error occurs. Therefore, it's only possible to speculate that the error is caused by the null value of $pdo when the prepare() method is called.

3. Class Method Initialization:
The methods fetch_all() and fetch_data() in the Category class both rely on the $pdo variable, so they should only be called after the $pdo variable has been initialized successfully in the global scope.

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