Trying to display from mySQL using a class in php - php

Question

I'm beginning php/MySql and have been asked to use a class to access my database. I can get the display to work when I have all my code in one file but when I try to call the class from another file, I get nothing.
This is the one that works:
<?php
$host = 'localhost';
$username = 'root';
$password = '';
$dbname = 'testdb';
$myNewConnection = mysqli_connect($host,$username,$password,$dbname);
$query = "SELECT user_name FROM users" or die ("Error..." . mysqli_error($myNewConnection));
// execute the query
$result = $myNewConnection->query($query);
// display output
while($row = mysqli_fetch_array($result)) {
echo $row["user_name"] . "<br>";
}
?>
This is my code to call the class:
<?php
include("users.php");
$host = 'localhost';
$username = 'root';
$password = '';
$dbname = 'testdb';
//initiate the class
$myDB = new MyDB('localhost', 'root', '', 'testdb');
//$myDB = new MyDB($host,$username,$password,$dbname);
?>
This is my class:
<?php
class MyDB {
public $query;
public $myConnection;
public function _construct($host,$username,$password,$dbname){
// establish the connection
$this->myConnection = mysqli_connect($host,$username,$password,$dbname);
}
public function list_users() {
// create query to list all users
$this->query = "SELECT user_name FROM users" or die ("Error..." . mysqli_error($this->$myNewConnection));
// execute the query
$result = $this->$myConnection->query($this->$query);
// display output
while($row = mysqli_fetch_array($result)) {
echo $row["user_name"] . "<br>";
}
}
}
?>
Any help appreciated

Answer 1

Change this line as below (remove the dollar sign from query and myConnection):
$result = $this->myConnection->query($this->query);
Plus you might need to call your list_users function using the code below (right after instantiating your class! Pass your defined variables to constructor instead of their actual values):
$myDB = new MyDB($host,$username,$password,$dbname);
$myDB->list_users();
Also constructors are written with two underscores like this:
public function __construct

Answer 2

function __construct with two "_". Delete all "$" after "->":
<?php
class MyDB {
public $query;
public $myConnection;
public function __construct($host,$username,$password,$dbname){
$this->myConnection = mysqli_connect($host,$username,$password,$dbname);
}
public function list_users() {
$this->query = "SELECT user_name FROM users";
if($result = $this->myConnection->query($this->query)) {
while($row = mysqli_fetch_array($result)) {
echo $row["user_name"] . "<br>";
}
}
}
}
And you have to run list_users():
<?php
include("users.php");
$host = 'localhost';
$username = 'root';
$password = '';
$dbname = 'testdb';
$myDB = new MyDB($host, $username, $password, $dbname);
$myDB->list_users();
?>