codeshare.php

<?php

class User 
{
    // Resolution access could change to readonly to make object immutable
    public string $id;
    public string $firstName;
    public string $lastName;

    public function __construct(string $id, string $firstName, ?string $lastName)
    {
        $this->id = $id;
        $this->firstName = $firstName;
        $this->lastName = $lastName;
    }
}



class Database 
{
    public static function query($query, $id) {
      	// ... database returns $row

        return new User($row['id'], $row['firstName'], $row['lastName']);
    }
}

class UserDatabase extends Database
{
    public static function findUsers($ids) {
        foreach ($ids as $id) {
            $results[] = UserDatabase::findById($id);
        }
        return $results;
    }

    public static function findById($id) {
        return Database::query("SELECT `firstName`,`lastName` FROM `users` WHERE `id`=" . $id, $id);
    }
}

class UserService {
    public function findUsers($ids) {
        $users = UserDatabase::findUsers($ids);
        if($users == null) {
            throw new Exception('Users not found!');
        } 

        return $users;
    }
}

$userService = new UserService();

class Application {

    public function run(){
        $users = $userService->findUsers([1, 2, 3]);
        
        foreach ($users as $user) {
            var_dump($user->id);
		    var_dump($user->firstName);
		    var_dump($user->lastName);
        }
    }
}


$application = new Application();
$application->run();