How to use PDO connection in other classes? - php

Question

I think I've a problem in understanding how OOP works. I already changed the code that it works, but it isn't the propper way I think. Following scenario (No, I'm not creating a userlogin by myself, its really just for local dev. to understand OOP better):
I've a database.php file:
class Database {
/* Properties */
private $conn;
private $dsn = 'mysql:dbname=test;host=127.0.0.1';
private $user = 'root';
private $password = '';
/* Creates 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'm creating a database connection and I return the connection (object?)
Then I have a second class, the famous User class (actually I'm not using autoload, but I know about it):
include "database.php";
class User {
/* Properties */
private $conn;
/* Get database access */
public function __construct() {
$this->conn = new Database();
}
/* Login a 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;
}
}
}
So thatare my two classes. Nothing big, as you see. Now, don't get confued about the function name login - Actually I just try to select some usernames and usermails from database and displaying them. I try to achieve this by:
$user = new User();
$list = $user->login();
foreach($list as $test) {
echo $test["username"];
}
And here comes the problem. When I execute this code, I get the following error message:
Uncaught Error: Call to undefined method Database::prepare()
And I'm not sure that I really understand what causes this error.
The code works well when I change the following things:
Change $conn in database.php to public instead of private (I think thats bad...? But when its private, I can only execute querys inside of the Database class, I'm right? So should I put all these querys in the Database class? I think that's bad, because in a big project it will get become really big..)
And the second change I've to do is:
Change $this->conn->prepare to $this->conn->conn->prepare in the user.php file. And here I've really no Idea why.
I mean, in the constructor of the user.php I've a $this->conn = new Database() and since new Database will return me the connection object from DB class, I really don't know why there have to be a second conn->

Answer 1

Do not create classes such as your Database class as it's rather useless. It would make sense to create a database wrapper if it adds some extra functionality to PDO. But given its current code, better to use vanilla PDO instead.
Create a single $db instance from either vanilla PDO or your database class.
Pass it as a constructor parameter into every class that needs 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 proper) PDO tutorial for more PDO details.