Class 'Db' not found - php

Question

When I attempt to connect to my SQL database with my pdo_object.php file, my model.php returns this error:
Fatal error: Class 'Db' not found in /path/model.php on line 8
I made sure all of the permissions are correct and credentials are correct for all of my files. Here are the two files in question.
Not really sure what the issue is here so any help would be awesome.
pdo_object.php
<?php
$user = 'someusername';
$pass = 'somepassword';
$db_info='somehost';
try {
$db = new PDO($db_info, $user, $pass);
} catch (PDOException $e) {
print "Error!: " . $e->getMessage() . "<br/>";
die();
}
?>
and then model.php
<?php
include('pdo_object.php');
class Model{
public $db;
public function __construct(){
$this->db = Db::getDb();
}
public function getAllRecords($sql, $parameters = null){
$stm = $this->db->prepare($sql);
$stm->execute($parameters);
return $stm->fetchAll();
}
public function getOneRecord($sql, $parameters = null){
$stm = $this->db->prepare($sql);
$stm->execute($parameters);
return $stm->fetch();
}
}
?>

Answer 1

Where is class Db { //blah }? Nowhere. But you HAVE defined $db in the first file.
I also recommend dependency injection, rather than calling static class methods inside your class. Essentially, pass the $db in in the constructor:
public function __construct(PDO $db)
{
$this->db = $db;
}
And instantiate like so:
$model = new Model($db);

Answer 2

The Db class was not present in the pdo_object.php file, thus resulting in the index.php file throwing an error when referencing a non existing class.
class Db {
private static $db;
public static function getDb() {
if(!self::$db) {
try {
$dsn = 'somehost; dbname=somedbname';
self::$db = new PDO($dsn, 'username', 'password');
self::$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
self::$db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);
} catch (PDOException $e) {
die('Connection error: ' . $e->getMessage());
}
}
return self::$db;
}
}