PHP OOP: How do I create a database class? - php

Question

Currently, my website runs procedural PHP. I would like to achieve to have a database class that can be used for other classes.
STATUS QUO:
On every page I include my dp.php before my header.php, the content and footer.php appear. My db.php looks like this:
// Credentials
$dbhost = "localhost";
$dbname = "dbname";
$dbuser = "dbuser";
$dbpass = "dbpassword";
// Connection
global $db;
$db = new mysqli();
$db->connect($dbhost, $dbuser, $dbpass, $dbname);
$db->set_charset("utf8");
// Check Connection
if ($db->connect_errno) {
printf("Connect failed: %s\n", $db->connect_error);
exit();
}
GOAL:
Having a database object that I can integrate into the EventData class that I have been building. The desired function of this class is that it will allow me to easily access data of my events table on any page. My EventData-class.php looks like this:
Class EventData {
private $_db;
private $_event_id;
public function __construct($eventID) {
$this -> _event_id = $eventID;
}
public function getValue($fieldname) {
// Build query for getting event details
$query = 'SELECT * FROM events WHERE id=' . $this -> _event_id . '';
// Do Search
$results = $db->query($query);
// Store all event details available in variables
while ($result = $results->fetch_assoc()) {
$value = $result[$fieldname];
}
// Return value
return $value;
}
}
I am new to OOP and am interested in learning how I need to modify both db.php and EventData-class.php in order to work.

Answer 1

The answer is brief and needs some your effort to improve or encode the idea.
First of all create a collection of items, something like this
class EventCollection {
protected $items = array(); // I keep protected so only addItem, removeItem etc. can be used to handle data
public $database = NULL;
public function addItem(EventData $item){
$this->items[] = $item;
$item->collection = $this; // this allows your EventData object to refer to its container
}
public function clear(){
$this->items = array();
}
public function __construct(mysqli $datb){ // inject mysqli object
$this->database = $datb;
}
public function removeItem... etc.
}
Having prepared the collection class, just update your EventData (consider creating a child class) by $collection field:
class EventData {
private $_db; // throw this away, not necessary
private $_event_id;
public $collection = NULL;
// etc.
Then in your main code create a $db variable as you do. Then create a (empty) collection:
$myEventCollection = new EventCollection($db);
and add items by
$myEvent = ....;
$myEventCollection->add($myEvent);
To refer to $db value inside the EventData class use something like this
class EventClass { ....
public function updateEvent(){
$this->collection->database->query('UPDATE ...');