将变量转化为类'

Question

So I've learnt a lot about PHP, and I started with the basics even if some of it is deprecated. Now I've got the knowledge down, I'm re-writing everything I've done to use PDO and class'. Now I've never used either but I'm slowly (slowly, slowly) understanding and getting my head around it. What I'd like to ask, is if I'm doing this right, if not where am I going wrong?

I basically have this function:

function user_exists($username) {
    $username = sanitize($username);
    $query = mysql_query("SELECT COUNT(`user_id`) FROM `users` WHERE `username` = '$username'");
    return (mysql_result($query, 0) == 1) ? true : false;
}

And I want to turn it into a class:

class user {
    function exists($username) {
        $username = $username;
        $query = $db->query("SELECT COUNT(`user_id`) FROM `users` WHERE `username` = '$username'");
        $results = $query->fetchAll(PDO::FETCH_ASSOC);
    }
}

Am I on the right track, should I be making the variables in that function (method) private to the "exists" method?

I plan to make a "users" class, with methods such as exists, banned, admin, ect. I think this is what I should be doing?

Thanks if anyone answers this.

Answer 1

class User {
    public $name;

    private $db;

    function __construct($name) {
        $this->name = $name;

        $this->db = get_me_a_db_connection();
    }

    public function exists() {
        $query = $this->db->query('SELECT COUNT(user_id) FROM users WHERE username = "' . $this->name . '"');
        $results = $query->fetchAll(PDO::FETCH_ASSOC);

        return some_code_that_extracts_the_count_from_$results;
    }
}

But: 1) $db should not be a class property. It should at least be in a factory. So you extract it in a factory:

class Factory {
    public static function db() {
        return get_me_a_db_connection();
    }
}

public function exists() {
    $query = Factory::db()->query(...);
    ...
}

This way you don't pollute your domain models with infrastructure code that much.

2) By that much above I mean you can achieve total decoupling between infrastructure code (database connection, querying) and your domain models. There are tons of libraries out there doing just that. I'd start with Laravel's Eloquent.

3) PDO queries are safe if you use prepared statements. All the libraries like the ones I linked to above use prepared statements. As a noob I would recommend you start learning by studying one of them.