Slim Framework - PDO object created but seems not inside the scope - php

Question

I get this error when I try to test my codes.
Call to a member function prepare() on a non-object in ........
Below is my codes :
ConnectionStrings.php
<?php
$config = require dirname(__FILE__).'../../Configs/Local.php';
$host = '127.0.0.1';
$db = 'CWW_SecurityDB';
$user = $config['db']['user'];
$pass = $config['db']['password'];
$charset = 'utf8';
$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
PDO::ATTR_EMULATE_PREPARES => false,
];
$pdo = new PDO($dsn, $user, $pass, $opt);
?>
Authentication.php (Related part)
<?php
use \Psr\Http\Message\ServerRequestInterface as Request;
use \Psr\Http\Message\ResponseInterface as Response;
require dirname(__FILE__).'../../../ConnectionStrings.php';
$app -> group('/authentication', function(){
$this -> Get('/login',
function($request, $response, $args)
{
$Username = $request->getQueryParams()['Username'];
$Password = $request->getQueryParams()['Password'];
$sql = 'CALL SEC.usp_GetSecurityUsers(:Username)';
$stmt = $pdo -> prepare($sql);
$stmt -> bindParam(':Username', $Username, PDO::PARAM_STR);
$stmt -> execute();
.
.
. (just a try out on the codes)
The problem should lie in the line $stmt = $pdo -> prepare($sql);. However, I really could not figure it out after hours. I have read some other posts with similar issue suggesting that the $pdo is out of scope.. but how exactly is my $pdo out of scope in this case? Can someone please enlighten me. Thank you in advance guys :)

Answer 1

In PHP, you don't have global variables automatically available in the function scope (more on variable scope). Inside the function, $pdo needs to either be defined or somehow made available. Few ways come to my mind:
Using global $pdo; in the function start - very old-school and won't be generally preferred way by php professionals.
Replacing $pdo with $GLOBALS['pdo'] - pretty much the same thing, kind of PHP3 style :)
Pass $pdo to the closure's scope:
$app->group('/authentication', function() use ($pdo) {
$this->Get('/login', function($request, $response, $args) use ($pdo) {
Fetch $pdo through dependency container (Slim3 uses Pimple for that):
// Store $pdo in DI container.
$container = $app->getContainer();
$container['database'] = $pdo;
...
// Then inside route controller:
$pdo = $this->get('database');