How to use PDO connection in other classes

Question

I feel like I have a problem understanding how object-oriented programming (OOP) works. I've changed the code so that it works, but I don't think it's the right way. Here's a scenario (no, I'm not creating the user login myself, this is just to understand OOP better):

I have a database.php file:

class Database {

    /* Attributes */
    private $conn;
    private $dsn = 'mysql:dbname=test;host=127.0.0.1';
    private $user = 'root';
    private $password = '';

    /* Create database connection */
    public function __construct() {
        try {
            $this->conn = new PDO($this->dsn, $this->user, $this->password);
        } catch (PDOException $e) {
            print "Error!: " . $e->getMessage() . "";
            die();
        }
        return $this->conn;
    }
}

So in this class, I create a database connection and return the connection (object?)

Then I have a second class, the famous User class (actually I don't use autoloading, but I know about it):

include "database.php";

class User {
    /* Attributes */
    private $conn;

    /* Get database access */
    public function __construct() {
        $this->conn = new Database();
    }

    /* Login user */
    public function login() {
        $stmt = $this->conn->prepare("SELECT username, usermail FROM user");
        if($stmt->execute()) {
            while($rows = $stmt->fetch()) {
                $fetch[] = $rows;
            }
            return $fetch;
        }
        else {
            return false;
        }
    }
}

These are my two classes. As you can see, no big deal. Now, don't be confused by the function name login - actually, I'm just trying to select some usernames and usermails from the database and display them. I tried to achieve it by:

$user = new User();
$list = $user->login();

foreach($list as $test) {
    echo $test["username"];
}

There is a problem here. When I execute this code I get the following error message:

Uncaught Error: Call to undefined method Database::prepare()

I'm not sure I really understand the cause of this error.

The code works fine when I change the following:

Changed $conn in database.php from private to public (I think this is bad...? But when it is private, I can only use it in the Database class Query is executed internally, right? So should I put all these queries in Database class? I think this is bad because in a big project it will become very huge...)

;

The second change is:

Change $this->conn->prepare in the user.php file to $this->conn->conn->prepare< /code>. I really have no idea about this.

I mean, in the constructor of user.php, I have a $this->conn = new Database(), Since new Database will return the connection object from the DB class, I really don't know why there must be a second conn->

Answer 1

• Don't create a class like Database because it is of little use. It makes sense to create a database wrapper class if it adds some extra functionality to PDO. But given its current code, it's better to use raw PDO.
• Create a single $db instance from the original PDO or your database class.
• Pass it as a constructor parameter to every class that requires a database connection.

database.php:

<?php
$host = '127.0.0.1';
$db   = 'test';
$user = 'root';
$pass = '';
$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);

user.php

<?php
class User {
    /* Properties */
    private $conn;

    /* Get database access */
    public function __construct(\PDO $pdo) {
        $this->conn = $pdo;
    }

    /* List all users */
    public function getUsers() {
        return $this->conn->query("SELECT username, usermail FROM user")->fetchAll();
    }
}

app.php

include 'database.php';
$user = new User($pdo);
$list = $user->getUsers();

foreach($list as $test) {
    echo $test["username"],"\n";
}

output:

username_foo
username_bar
username_baz

Check out my (the only correct) PDO tutorial for more details on PDO.