PHP PDO class construction - php

Question

I'm pretty new to both PDO and OOP. I'm trying to write a class that connects to a database and updates inserts and modifies it. I have several questions:
Is it good practices to connect to the database in the constructor?
Should the one class be updating, inserting, modifying and connecting or should it be split up into several classes?
Why is runQuery not working? I assume its because $pdo is defined in a different scope. How would I get this working?
If the class is include at the top of every page does that mean it will reconnect to the database every time a new page is loaded and will that cause security issues?
Apologies for the overload of questions. Thanks in advance for any answers.
<?php
class Login{
private $_username;
private $_password;
private $_host;
private $_database;
private $_driver;
//Connect to the database
function __construct($configFile){
$connectionDetails = parse_ini_file($configFile);
$this->_username = $connectionDetails['username'];
$this->_password = $connectionDetails['password'];
$this->_host = $connectionDetails['host'];
$this->_database = $connectionDetails['database'];
$this->_driver = $connectionDetails['driver'];
$pdo = new PDO("$this->_driver:host=$this->_host;dbname=$this->_database", $this->_username, $this->_password);
}
public function loginAllowed($user, $pw){
$sth = $pdo->setFetchMode(PDO::FETCH_ASSOC);
print_r($sth);
}
public function runQuery($query, $params){
$sth = $this->pdo->prepare($query);
$sth->execute($params);
}
}

Answer 1

Because $pdo is a local variable in your constructor and your method loginAllowed. You should make it an instance variable (private $pdo) so you can call it through $this->pdo. I also suggest to use type hinting here, give the PDO class as a parameter in the constructor.
Example
<?php
class Login {
private $pdo;
// Your other instance variables
public function __construct(PDO $pdo)
{
$this->pdo = $pdo;
}
// Your other methods
}
$pdo = new PDO("...");
$login = new Login($pdo);
You shouldn't bother your class with reading settings and initialising your database connection (definitely read about separation of concerns), keep it out of your class. Just give the PDO object as a parameter (I used type hinting, that way you are forced to provide an object of the PDO type). Another advantage is that you can now make sure you have only one active database connection (you can manage this in your code base), creating multiple connections is unnecessary and definitely unwanted (performance wise).
Also use require_once to include your class definition. Otherwise you will get many errors about redeclaring (and you'd want to avoid that).

Answer 2

Connect to the db wherever you find it most convenient. Just try to make sure there's only ONE connection. More connections to the same db is a waste of time and resources.
The class you refer to is called a model in the MVC architecture. It usually does all the operations on a given table. I see nothing wrong in using a single class for all your needs - as long as the code is readable and maintainable.
It's not working because $pdo is a local variable. In the ctor, instantiate $this->pdo instead.
Including a class is not equivalent to instantiating it. A new instance will make another connection. Including it multiple times will only give you a multiple declaration error :). Use require_once instead. If you wish to use the instance in multiple files, I strongly suggest you do a quick search regarding the Singleton pattern. Using a singleton object will ensure you always have only one instance of your model object.

Answer 3

Don't bother with all the random stuff, just replacethis in your construct:
$pdo = new PDO("$this->_driver:host=$this->_host;dbname=$this->_database", $this->_username, $this->_password);
with
$this->pdo = new PDO("$this->_driver:host=$this->_host;dbname=$this->_database", $this->_username, $this->_password);
and reference it as $this->pdo from now on. As simple as that!!

Answer 4

1) Is it good practices to connect to the database in the constructor?
No good.just connect befor query
if($this->pdo == null) {
$this->pdo = new PDO("....");
}
2) Should the one class be updating, inserting, modifying and connecting or should it be split up into several classes?
Add methods for class
3) Why is runQuery not working? I assume its because $pdo is defined in a different scope. How would I get this working?
use $this->pdo instead
4) If the class is include at the top of every page does that mean it will reconnect to the database every time a new page is loaded and will that cause security issues?
use static $pdo
then self::$pdo would be the only one connector
if(self::$pdo == null) {
self::$pdo = new PDO("....");
}