How to instantiate PDO class functionality (::prepare method) in another class - php

Question

I'm refactoring my PHP code, so that the insertion of data into my database is kept separate from the class that creates the database connection. I'm trying to implement the Single Responsibility Principle, but transferring my code (for inserting data) to a separate class results in the PDO::prepare statement becoming an 'undefined method'.
I have tried to instantiate my database class ('DB.php') and pass the object to the class that inserts data ('Register.php').
The DB class:
<?php
class DB
{
public $dbServer,
$dbUsername,
$dbPassword,
$dbName,
$pdo,
$stmt;
function __construct($dbServer,
$dbUsername,
$dbPassword,
$dbName)
{
$this->dbServer = $dbServer;
$this->dbUsername = $dbUsername;
$this->dbPassword = $dbPassword;
$this->dbName = $dbName;
$this->connect();
}
public function connect()
{
try {
$this->pdo = new PDO("mysql:host=" . $this->dbServer .
"; dbname=" . $this->dbName,
$this->dbUsername,
$this->dbPassword);
$this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e) {
exit("Could not connect to database: " . $e->getMessage() );
}
}
}
The Register class:
<?php
class Register
{
public $pdo,
$dbh,
$stmt,
$conn;
function __construct(DB $pdo)
{
$this->pdo = $pdo;
// $this->conn = $this->pdo->connect();
}
public function register(Validate $val)
{
try {
$this->stmt = $this->pdo->prepare(
"INSERT INTO registration(firstName,
surname,
email,
username,
password,
gender,
area)
VALUES(:firstName,
:surname,
:email,
:username,
:password,
:gender,
:area)");
$this->stmt->bindParam(':firstName', $val->firstName);
$this->stmt->bindParam(':surname', $val->surname);
$this->stmt->bindParam(':email', $val->email);
$this->stmt->bindParam(':username', $val->username);
$this->stmt->bindParam(':password', $val->password);
$this->stmt->bindParam(':gender', $val->gender);
$this->stmt->bindParam(':area', $val->area);
$this->stmt->execute();
} catch(PDOException $e) {
echo 'Error: ' . $e->getMessage();
}
}
}
My Configuration file:
<?php
$dbServer = '127.0.0.1';
$dbUsername = 'root';
$dbPassword = '';
$dbName = 'assignment';
spl_autoload_register(function($class)
{
require 'classes/' . $class . '.php';
} );
$db = new DB($dbServer, $dbUsername, $dbPassword, $dbName);
$database = new Register($db);
The actual Registration page:
<?php
require('core/config.php');
if( isset($_POST['submit']) ) {
$firstName = $_POST['firstName'];
$surname = $_POST['surname'];
$email = $_POST['email'];
$username = $_POST['username'];
$password = $_POST['password'];
$gender = $_POST['gender'];
$area = $_POST['area'];
$val = new Validate($firstName, $surname, $email, $username, $password, $gender, $area);
$val->filter();
$database->register($val);
}
?>
This implementation results in the following notice:
Fatal error: Uncaught Error: Call to undefined method DB::prepare()
Why doesn't the PDO class communicate its in-built prepare() function to my Register class? I have viewed 'Fatal error: Call to undefined method Database::prepare()' on Stack Overflow and sought to remedy my code:
$this->conn = $this->pdo->connect();
(See the commented statement in my Register class.) However, $this->conn ends up returning a NULL instead of my database connection.