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

Question

These are three files

config.php
functions.php
index.php

I got an error \"Fatal error: Uncaught Error: Call to a member function prepare()

Answer 1

You will not get the $pdo variable in DatabaseConnection class from global scope. So, your $pdo variable is basically null. You can change you code as below:

config.php:

class DatabaseConnection {
   public function __construct() {
      try {
         return new PDO('mysqli:host=xxx;dbname=xxx', 'root', '');            
      } catch(PDOException $e) {
          exit('Database error');
      }
   }
}

Then:

class LoginRegistration {
    private $database

    function __construct() {
        $this->database = new DatabaseConnection();
    }

    public function registerUser($username, $password, $name, $email, $website) {

      $query = $this->database->prepare("SELECT id FROM users WHERE username = ? AND email = ?");
      $query->execute(array($username, $email));
      $num = $query->rowCount();

      ...

However, I would rather extend the DatabaseConnection class rather instantiating it within the LoginRegistration class. That is:

config.php:

class DatabaseConnection {
   protected $pdo;
   public function __construct() {
      try {
         $this->pdo = new PDO('mysqli:host=xxx;dbname=xxx', 'root', '');            
      } catch(PDOException $e) {
          exit('Database error');
      }
   }
}

Then extend DatabaseConnection from LoginRegistration class:

class LoginRegistration extends DatabaseConnection {
    // constructor is not needed anymore
    public function registerUser($username, $password, $name, $email, $website) {

      $query = $this->pdo->prepare("SELECT id FROM users WHERE username = ? AND email = ?");
      $query->execute(array($username, $email));
      $num = $query->rowCount();

      ...