Cant get results out database oophp, mysqli - php

Question

im trying to understand oophp a litle bit but now im stuck in getting information out of my database. What am i doing wrong? After the tip off PDO I tried the following but also no results...
index.php
<?php
include('classes/database.class.php');
$db = new Database();
$db->connect();
$res = $db->select();
print_r($res);
?>
database.class.php
<?php
class Database {
private $db_host = 'localhost'; // Database Host
private $db_user = 'root'; // Gebruikersnaam
private $db_pass = 'root'; // Passwoord
private $db_name = 'quickscans'; // Database naam
public function connect()
{
try
{
$db = new PDO('mysql:host='.$this->db_host.';dbname='.$this->db_name,$this->db_user,$this->db_pass);
}
catch(PDOException $e)
{
echo $e->getMessage();
}
}
public function disconnect()
{
$db = null;
}
public function select()
{
$sql = 'SELECT id FROM bedrijf';
$results = $db->query($sql);
foreach($results as $row)
{
echo $row['id'].'<br>';
}
}
}
?>
Maybe this code is a bit cleaner.. but still no results :(.

Answer 1

You aren't assigning any instance variables in this class.
The query method has no access to the connection you create because the object has no state.
Your constructor for the class should create the connection, and then queries can be called on this property.
class Database {
private $db_host = 'localhost'; // Database Host
private $db_user = 'root'; // Gebruikersnaam
private $db_pass = 'root'; // Passwoord
private $db_name = 'quickscans'; // Database naam
public function __construct(){
$this->connect();
}
public function connect()
{
try
{
$this->connection = new PDO('mysql:host='.$this->db_host.';dbname='.$this->db_name,$this->db_user,$this->db_pass);
}
catch(PDOException $e)
{
echo $e->getMessage();
}
}
public function disconnect()
{
$this->connection = null;
}
public function select()
{
$sql = 'SELECT id FROM bedrijf';
$results = $this->connection->query($sql);
foreach($results as $row)
{
echo $row['id'].'<br>';
}
}
}
The $this keyword sets instance variables for the class, so the connection property becomes a PDO instance that other methods can act upon. Without this, the varibles created in the methods, in this case $db are just orphaned in the local function scope and not accessible in the greater class.
Utilizing this approach elminates the need to run connect() in the calling context. You don't need to use the constructor to do this if you don't want to, you'll just always need to connect first in order to create the connection property and have it available to the rest of the class. Also note you can name the property whatever you like, I just used connection because it made the most sense in the API.
Also, as commented, to make this a bit more usable you should have the select method return the query results array rather than having it output directly.
public function select()
{
$sql = 'SELECT id FROM bedrijf';
$results = $this->connection->query($sql);
if(!empty($results)){
return $results
}else{
return false;
}
}