Interacting with PHP classes/functions properly? (OOP) - php

Question

I started using PHP classes and looked into OOP.
I played around by creating a Database class that looks something like this (snippet):
class Database
{
private $link;
private $result;
private $count;
function connect()
{
$this->link = mysql_connect(DB_HOST, DB_USER, DB_PW);
$return = $this->link ? 'Connected to database.' : 'Failed to connect.';
$this->open(); // I have another function in this class to select the db
echo $return;
}
function query($query)
{
$this->result = mysql_query($query);
}
function fetch()
{
return mysql_fetch_assoc($this->result);
}
function count()
{
$this->count = mysql_num_rows($this->result);
return $this->count;
}
}
Just to test, I created another class called Guestbook that looks like this:
class Guestbook
{
function fetch()
{
Database::query('SELECT * FROM guestbook LIMIT 2');
while($row = Database::fetch()){
$result_array[] = $row;
return $result_array;
}
}
Now I tested calling the functions:
$db = new Database();
$db->connect();
$db->query('SELECT * FROM test');
while($row = $db->fetch()) {
echo $row['id'].'<br />';
}
echo $db->count();
$db->close();
This works as expected. So I went on with the Guestbook class:
$db->connect();
$guestbook = new Guestbook();
$results = $guestbook->fetch();
foreach($results as $gb) {
echo $gb['id'];
}
echo $db->count(); // HERE'S MY PROBLEM !
$db->close();
Everything works as I wanted, but the second time I call $db->count() it echos the previous count and not 2 (as I set LIMIT 2 in the Guestbook fetch function).
How do I interact with these classes properly, so I can use something like $db->count() globally?
Thanks in advance for any hints or solutions!

Answer 1

First off, there is no reason to wrap mysql_* implementations in OOP. IF you are going to do OOP then just use Mysqli or PDO which have OOP classes you can extend.
Secondly you want to hold an instance of the Database in the GuestBook class, not make it an extension of the Database class itself.

Answer 2

It is hard to give you a definitive advice on how you could wrap your database accessor with OOP and still access the count() globally.
Clearly your code is wrong.
by using the notation
Database::query
you are referring to some kind of static methods on the Database class which does not seem to be the intent here. It looks like your code does not crash because of some backward compatibility with PHP4.
you could rewrite Guestbook along this way :
class Guestbook
{
private $db;
function __construct(&$db) {
$this->db = $db;
}
function fetch($option)
{
$this->db->query('SELECT * FROM guestbook LIMIT 2');
while($row = $this->db->fetch()){
$result_array[] = $row;
return $result_array;
}
}
and then
$db = new Database();
$db->connect();
$guestbook = new Guestbook($db);
$results = $guestbook->fetch();
echo $db->count();
This technique uses a pattern known as "Dependency Injection"

Answer 3

Why would you use count from the db class when you have the results from the guestbook->fetch() method?
This does exactly the same trick:
echo count( $resutls );

Answer 4

see the $db is a object of the class Database
never access the function OR property of the Guestbook
you can get this directly with count( $resutls )
OR may have to go with the inheritance concept
Thanks

Answer 5

You mixing static with instantiated versions of your class. If you want to be able to create multiple instances of a class, you should have a __construct function. While it's not required, it's best practice to have one.
You are creating a new instance and assigning it to the $db variable ($db = new Database();). But then in your GuestBook class you are referencing the database class statically (Database::). That syntax references the "base" class which is the same across all instances. What you want to do is reference the instance of the database class you created. Typically you would pass the database instance to use into the GuestBook class in the constructor, store that in a class variable, then reference it using $this.
class Guestbook
private $db = null;
{
function __construct($db) {
$this->db = $db;
}
function fetch($option) {
$this->db->query('SELECT ...');
...
}
}
$db = new Database();
$guestbook = new Guestbook($db);