A model implementation using the repository pattern. From the article: PDO for Elegant PHP Database Access, http://www.modernphpbook.com/articles/pdo-for-elegant-php-database-access - Fig 4

UserRepository.php

<?php 
class UserRepository
{
    public function __construct($dao = null)
    {
        if (!$dao) {
            $dao = new DataAccessObject();
        }
        $this->dao = $dao;
    }
    
    public function find($id)
    {
        return $this->query('
            SELECT * FROM users WHERE id = ' . (int)$id . '
        ');
    }
    // etc...
}

L14 I think you should put $this->dao(...) instead of $this->query(...)