Unable to add values with bindValue() to a pdo object - php

Question

I'm writing a registration script that checks if the username already exists.
First I had troubles getting my database instance from databaseconnection.php to registration.php, this was the error: Call to undefined method DatabaseConnection::prepare().
But now I'm getting past the prepare() line and want to give my values to the query with bindValue(), but this next error is what I get 'Call to a member function bindValue() on a non-object'.
Does this still means I didn't get the correct database instance but a instance of the databaseconnection.php class?
This is databaseconnection.php
<?php
class DatabaseConnection {
private static $instance = null;
public $db_connection;
private function __construct(){
try{
$this->db_connection = new PDO('mysql:host='. DB_HOST .';dbname='. DB_NAME, DB_USER, DB_PASS);
$this->db_connection->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
return true;
} catch (PDOException $exception){
$this->errors[] = $this->lang['Database error'];
return false;
}
}
public static function getInstance(){
if(self::$instance === null){
self::$instance = new DatabaseConnection();
}
return self::$instance;
}
public function __call($method, $args) {
$callable = array($this->pdo, $method);
//is_callable, verify that the contents of a variable can be called as a function
if(is_callable($callable)) {
return call_user_func_array($callable, $args);
}
}
}
?>
In registration.php I use this code to get the instance into my local private variable:
class Registration
{
private $db_connection = null;
public function __construct()
{
$this->db_connection = databaseConnection::getInstance();
...
}
...
}
And would like to be able to execute this query in registration.php:
...
$check_username_query = $this->db_connection->prepare('SELECT user_name, user_email FROM users WHERE user_name=:user_name OR user_email=:user_email');
$check_username_query->bindValue(':user_name', $user_name, PDO::PARAM_STR);
$check_username_query->bindValue(':user_email', $user_email, PDO::PARAM_STR);
$check_username_query->execute();
$results = $check_username_query->fetchAll();
...

Answer 1

$callable = array($this->pdo, $method);
You have instance of PDO in $this->db_connection not $this->pdo